CGRO Cycle 7 Approved Program Abstracts
GRO-97-083 BAND Previous studies of the evolution
of gamma-ray burst spectra have generally relied on fitting sequences of
spectra. These studies usually were confined to bright bursts and often
lacked sufficient temporal resolution. We propose studies wh ich sacrifice
spectral resolution for temporal resolution; our two techniques are the
crosscorrelations between intensity lightcurves in different energy bands,
and the energy correlation of pairs of counts. We wish to: determine whether
spectral evolutio n changes during a burst; isolate the spectral evolution
on different timescales; and search for short-duration, narrowband emission.
GRO-97-002 BARTHELMY We propose (1) to continue
to operate the BATSE Coordinates Distribution Network (BACODINE), (2) to
improve the GRB location accuracy of BACODINE & (3) agressively pursue
new customers & modify the operation to meet new site-needs. BACODINE
is a system that calculates GRB locations from the BATSE telemetry data
in real time & distributes those positions to instruments to make multi-band
follow-up observations of GRBs in real time -- less than 6 seconds. Our
approach allows the making of mu lti-band observations of the GRBs while
they are still in progress. BACODINE is providing a new tool for GRB research.
The current BACODINE site instruments are setting ever more stringent upper
limits at ever short time delays. The recent SAX observation s have shown
that near-realtime follow-up observations are critical to counterpart identification.
Continued operations will improve the these limits & allow for more
counterpart identifications.
GRO-97-070 BASSANI We propose a multiyear project
to continue our previous study of all active galaxies in the Piccinotti
sample using BATSE. We intend to exploit the Earth occultation technique
to search for emission in the 20-100 keV band from these bright galaxies.
The sample represents the only unbiased and complete 2-10 keV survey of
the sky down to a limiting flux of 3.1x10^(-11) erg/cm2/s. As such this
sample has been used to construct the LogN-LogS relation as well as the
luminosity function of activ e galaxies in the 2-10 keV band allowing a
determination of the AGN contribution to the X-ray background. BATSE data
from three years of observations have already been analyzed and here we
propose to extend this by adding data after October 95. With the c ontinuous
monitoring of this sample, BATSE can record both intensity and spectral
information about the brightest objects. Spectral and variability analysis
at high energies on these AGN will be performed.
GRO-97-040 BERTSCH The EGRET observations of the
June 1991 series of flares provided spectral and temporal measurements
of high energy gamma ray emissions up to 1 GeV, lasting hours after the
impulsive phase. Spark chamber and energy calorimeter observations provided
information on the spectrum of accelerated particles at the Sun, and on
their interactions and confinement. We propose a multi-year study to analyze
all EGRET data in the calorimeter and all spark chamber data when the Sun
flares in the field of view. Targets of Opportunity are requested under
specific circumstances outlined in the proposal.
GRO-97-148 BLOEMEN We propose to complete a deep
COMPTEL exposure of the Orion/Mon region (2 x 4 weeks) to extend and improve
upon our study of nuclear deexcitation lines. This proposal is an update
of our Cycle-6 proposal, which was accepted and scheduled ( 9 weeks), but
only 5 weeks of good data will become available because of a ToO observation
and because of observations during the period of reboost activities in
March/April 1997. We wish to reduce the strong asymmetry in the currently
available exposure and obtain a set of observations that is less influenced
by the Crab. These additional observations, in combination with available
data, will allow us to map the complex in narrower energy bands and improve
significantly upon our spectral analysis, which is crucial for determining
the origin of the emission.
GRO-97-131 BRAINERD We propose a study of whether
the BATSE gamma-ray burst E-peak distribution is a consequence of instrumental
effects. Resolution of this question is vital for the development of new
theories. The proposed study will resolve it by answering these two questions:
are the observed E-peak values correct, and is the triggering on a gamma-ray
burst sufficiently independent of E-peak to make the observed E-peak distribution
an accurate representation of the physical distribution? We will answer
th ese questions through the following methods: by folding model spectra
through the BATSE DRMs and deriving both the detection efficiency and the
observed E-peak as a function of true E-peak; by examining the E-peak distributions
found for BATSE bursts dete cted under various triggering criteria; by
examining the detection of soft sources such as SGRs and hard sources such
as TGFs by BATSE; and by comparing the burst characteristics found by BATSE
to those found by Comptel.
GRO-97-133 BRIGGS The BATSE team effort to find
lines in GRBs has found 17 significant candidates in 118 bright GRBs. We
propose the analysis required to determine the reality of these candidates:
when multiple Spectroscopy Detectors observed a candidate, w e will analyze
that data for consistency or confirmation; we will evaluate the significance
of the candidates considering alternative, reasonable continuum models;
and we will evaluate the significance of the candidates considering the
large number of spe ctra that were searched. The goal of this project is
to determine whether or not low-energy (below 100 keV) spectral features
exist in GRBs observed by BATSE. After reaching a conclusion on the reality
of the features, we will either set limits on the exi stence of lines or
characterize the distribution of line parameters.
GRO-97-229 BUCKLEY Motivated by the recent discovery
of a high level of 50-150 keV emission from the BL Lac object Mrk 501 coincident
with a period of intense flaring at TeV energies, we propose two weeks
of observations of Mrk~501 with the Whipple Gamma-Ray Telescope, OSSE,
and the Whipple Observatory's 1.2m optical telescope. We also propose a
target of opportunity observation of Mrk 421 when the TeV flux exceeds
the flux of the Crab Nebula. The OSSE detection of Mrk 501 and PKS 2155-304,
as well as the ha rd X-ray spectrum observed for Mrk 421 in its high state,
imply that Mrk 421 will also be detected with OSSE. These measurements
should determine whether the apparent extension of the synchrotron emission
of Mrk 501 to 100 keV is always present, or only o ccurred as a result
of the intense flaring in April 1997, and whether this feature is unique
to Mrk 501. Measurements of spectral cutoffs in the OSSE and Whipple wavebands
constrain the physical properties of the blazar jets. !
GRO-97-088 CARRAMINANA Among gamma-ray pulsars,
PSR B1509-58 is unique, with its gamma-ray spectrum not extending beyond
the MeV range. It provides a powerful test for models: the polar cap model
naturally predicts a cut at a few MeV, through magnetic photon pro cesses;
the outer gap model accomodates MeV emission as a synchrotron component.
The fluxes measured by COMPTEL for PSR B1509-58 are particularly constraining
and may turn out to be decisive for the physical intepretation. However,
partly because of the s carcity of specifically aimed observations, the
present signal to noise is still low: the only report from an individual
observation comes from the only pointing at less than 10 deg of the COMPTEL
axis. We propose to observe PSR B1509-58 for five weeks, t hree of them
with the pulsar close to the pointing axis. The resulting data will be
analyzed together with archive data, using contemporaneous radio ephemerides.
GRO-97-136 CATANESE We propose to conduct a Target
of Opportunity Observation of a nearby X-ray selected BL Lac object with
CGRO in coordination with the Whipple gamma-ray telescope and the Rossi
X-ray Timing Explorer when the object is in a high state of emi ssion.
Fifteen BL Lac objcets, not previously detected by the Whipple telescope
above 300 GeV, will be monitored for high state activity by both the Whipple
gamma-ray telescope and the RXTE All-Sky Monitor. The ToO would be triggered
by observation of a h igh state in the >300 GeV emission as detected
with the Whipple gamma-ray telescope, if it lasts for at least a one week
period. This technique yielded spectacular results with Mrk 501. By requiring
an extended high state before declaring the ToO, the pro bability that
a flare will be detected with multiple telescopes is high. Such an observation
provides an excellent test of blazar emission models.
GRO-97-075 COE The proposal requests any BATSE
data recorded during outbursts from eight Be/X-ray binary systems. Observing
time on the Infrared Space Observatory has been aproved as Target of Opportunity
observations should any of these systems go in to outburst. Since all these
systems are both IR bright and X-ray bright during these outbursts we seek
matching data from BATSE. All these systems are also being monitored by
us at near-IR and optical wavelengths.
GRO-97-094 COLLMAR The gamma-ray blazar PKS 0528+134
has been previously detected by COMPTEL several times. The source shows
evidence for a time-variable MeV-flux and spectrum, and for a correlated
spectra-intensity behaviour which was found by a combined an alysis of
the simultaneous EGRET and COMPTEL data. During gamma-ray high-intensity
(flaring) states observed by EGRET, a "harder" MeV-spectrum is
observed than during gamma-ray low intensity (non-flaring) states. The
combined, simultaneous COMPTEL/EGRET s pectra indicate these two states
as well. The flaring state requires a spectral turnover at MeV-energies,
while for the non-flaring state a simple power-law model is sufficient
to describe the observed spectra. The observations are consistent with
an addi tional spectral component showing up at MeV-energies and above
during the gamma-ray flaring states. To further monitor PKS 0528+134, we
propose to continue the COMPTEL observations (0.75-30 MeV) with a continous
observation of! 4 weeks.
GRO-97-095 COLLMAR We propose to continue the
COMPTEL observations (0.75-30 MeV) of the Virgo sky region with a continous
observation of 4 weeks. The prime goal is to further monitor the MeV-behaviour
of the prominent Virgo blazars 3C 273 and 3C 279 in spect rum and flux
to derive informations e.g. on their spectral shapes at MeV-energies, on
possible spectra-intensity correlations, on duty cycles of high intensity
states, to provide the gamma-ray state for correlations with other wavelength
bands, and to par ticipate in collaborating observations on both sources.
Both blazars have been detected previously by COMPTEL several times, showing
a time-variable MeV-emission. An additional goal is to substantiate the
COMPTEL results (detections/indications) on furthe r MeV-emitting AGN sources
located in this sky region. For 3C 273 an EGRET observation is proposed
as well, to check its gamma-ray state (>100 MeV) in Cycle 7 which was
found at record heights in Cycle 6.
GRO-97-152 CONNAUGHTON We propose to undertake
a hard X-ray survey of 92 BL Lacertae objects using the source occultation
method developed by the BATSE team. A previous study of a sample of Active
Galactic Nuclei containing 4 BL Lacertae sources resulted in the detection
of 3 of these sources at a greater than 4 sigma significance level, showing
BATSE has the sensitivity to detect at least some of these weak X-ray sources.
It is proposed to investigate the emission levels and spectra of both X-ray-
and radio-sel ected BL Lac objects in an effort to examine hard X-ray differences,
if any, between the two classes. Recent results indicate that BATSE is
sensitive to certain soft X-ray-detected flares from BL Lac objects on
time-scales of days. Detection of strong, ha rd flares in lower energy
X-rays (e.g. by RXTE, SAX) will initiate a search for correlated emission
in BATSE data.
GRO-97-228 CONNORS The COMPTEL team has been operating
a Rapid Burst Response system, in collaboration with BACODINE and NMSU.
We have provided 1-2 degree localizations of bright gamma-ray bursts within
our field of view within roughly 10 minutes of burst on set. With a change
in Instrument Ground Station hardware, we have an opportunity to upgrade
our system to enable us to provide localizations within 1 minute of burst
onset, under the best conditions. While maintaining our current capability
until each upg rade is in place, we propose to: 1) port the current system
to the new hardware, with some improvements, to reduce response time to
6-10 minutes from burst onset; and 3) streamline the procedure and software
so response time can be as short as 1 minute fr om burst onset. This opens
the way for the fastest ground-based telescopes to respond to 1-2 degree
localizations while the high energy burst emission is still in progress.
GRO-97-156 COPPI We propose a two-week OSSE observation
of the Galactic Black Hole Candidate Source Cyg X-1 as part of a co-ordinated,
broad-band observing campaign involving OSSE, SAX, and XTE. The combination
of OSSE and SAX, in particular, will yield a unique data set, providing
simultaneous spectral coverage from 0.1 keV to over 400 keV with no no
energy gaps and fairly good time resolution. Data of this type is crucial
for understanding the physical conditions inside the gamma-ray emitting
region of C yg X-1 and the relation of this region to the accretion disk
of Cyg X-1 as a whole. With such data and the sophisticated emission codes
we have developed, we can strongly constrain: (i) the geometry of the gamma-ray
emission region, (ii) the origin of the soft photons which are presumably
being Compton upscattered to gamma-ray energies, (iii) the presence of
electron-positron pairs in this region, and (iv) the presence of a significant
non-thermal population of electrons and/o! r positrons.
GRO-97-164 CORDES We propose (1) new OSSE/EGRET
pointings for known radio pulsars that are ranked high according to our
likelihood analysis on CGRO data; (2) folding of archived and new data
using improved radio timing models developed by us; (3) a 3-day OS SE pointing
to the Crab pulsar to monitor its pulse shape; (4) A global likelihood
analysis on new and archived CGRO data to give a complete picture of spin
driven pulsars in gamma-rays; this will include upper bounds as well as
detections and will incorp orate radio polarization results that constrain
orientation angles relevant to beaming.
GRO-97-231 DANIEL The supernova occurrence rate
is a critical factor in the theory of nucleosynthesis. There are important
systematic uncertainties in the rates derived from optical surveys, due
to absorption and source confusion, such that those rates must be considered
lower limits. Those problems are negligible for the gamma-ray emission
from the Co-56 which is produced in a supernova explosion. Of the instruments
on CGRO, COMPTEL is the most sensitive to this emission as shown by its
detection of SN 199 1T. In a standard 14-day observation COMPTEL can detect
a type Ia supernova out to about 10 Mpc and other types to about 3 Mpc.
We propose to derive a rate or upper limit by searching all COMPTEL observations
for Co-56 emission and determining the sensiti vity to such emission from
each nearby galaxy in the field of view. To maximize the sensitivity measures
must be taken to deal with instrumental activation background, particularly
in data from the latter half of cycle three o! r later.
GRO-97-069 DEAN We propose a multiyear project
to study a sample of 40 AGNs using BATSE as an extension of two successful
CGRO guest investigations by the same team. The sample consists of 22 bright
(detectable at 5 sigma or more) and 18 fainter objects. Priority should
be given to the bright subset of AGN. The aim of the proposal is to enrich
the database of extragalactic objects already detected by BATSE having
as a final goal the production of a complete sample of AGN in the 20-100
keV band. The use of this database will both allow statistical studies
of the high energy characteristics of AGN and also permit the determination
of the LogN-LogS relation and the luminosity function at high energy. Thus
measurements in the BATSE energy range will help dete rmine the contribution
of AGN to the cosmic diffuse background. Furthermore, spectral and variability
information on the brightest sample objects will also enrich our knowledge
of the emission mechanisms and the size of the AG! N emitting region.
GRO-97-161 DENNIS We propose to conduct a comprehensive
analysis of CGRO solar flare x-ray data. We have assembled for this purpose
a team of scientists with expertise at all levels of the analysis process,
from instrument characterization to data reduction and interpretation.
The objective is to understand electron acceleration and transport in flares,
and their relationship to space weather. An additional objective is to
develop an early warning system for interplanetary particle events using
the BATSE Co ordinates Distribution Network (BACODINE). We also propose
to continue providing online access to the BATSE solar flare data for the
solar physics community, as we have since launch.
GRO-97-194 DERMER The recently discovered high-latitude
e$^+$-e$^-$ annihilation radiation feature towards the galactic center
region poses several interesting astronomical questions. These include
the sources of the positrons, for example, whether they are created by
nucleosynthetic decay processes or black hole production; the mechanisms
by which the positrons are transported to high altitudes and annihilate;
the implications of these observations on the activity taking place in
the central region of the Milky Way; and the relationship between our galaxy
and galaxies with starburst or nuclear activity. We propose to examine
these questions and produce model annihilation radiation maps which can
be fitted to the observations of the galactic diffuse 0.511 M eV annihilation
radiation. Studies of the line shape and spatial dependence of the annihilation
line and continuum radiation will be made which can be used to analyze
OSSE and high-resolution observations of this emission.
GRO-97-195 DERMER This is a renewal proposal to
continue archival EGRET analysis of radio-emitting AGNs which have not
been reported as EGRET sources. We have developed a new software package
for extracting from archival EGRET data counts, exposure, and dif fuse
galactic background maps which are suitable for co-adding. We have obtained
preliminary results on co-added archival EGRET data of known radio-loud
AGNs, selected on the basis of radio-spectral index, classification as
a radio- or X-ray selected BL L ac object, and detection in the OSSE band.
Other properties and source classes will also be considered. This research
tests unification studies of AGNs on the basis of orientation. We will
also continue to model spectral and temporal variability of radio galaxies
and blazars which can be tested by correlated multiwavelength observations.
GRO-97-096 DIEHL COMPTEL measurements revealed
a remarkable feature of 1.809 MeV gamma-ray line emission far away from
the inner Galaxy in the Cygnus region: Here a unique calibration of nucleosynthesis
models for the candidate 26Al source types appears po ssible, since the
morphology and the object population is well known. COMPTEL Observations
of the Cygnus region have been taken already, with a total of 41 days assembled
from 27 pointings altogether. However, strong background variations between
these sh ort observations and the frequently large off-axis angles of the
region of interest severly limits the cumulative sensitivity. We propose
to perform dedicated observations of the Cygnus region that minimize possible
systematic background uncertainties thr ough contiguous observations of
the region, but also account for second-order response impacts through
systematic 'dithering' of the pointing. With these observations, we expect
to separately identify emission from the Cygnus ! superbubble, and foregr
GRO-97-097 DIEHL COMPTEL measurements revealed
a remarkable feature of 1.809 MeV gamma-ray line emission far away from
the inner Galaxy in the Vela region, where a unique calibration of nucleosynthesis
calculation for two of the advertised candidate source types appears possible:
If the contribution from the Vela Supernova can be demonstrated to dominate
the observed 1.809 MeV signal, core-collapse supernova yield calculations
for this object need to reproduce the observed amount of 26Al. Additionally,
the nearest Wolf-Rayet star to the Sun at <300pc distance should be
at COMPTEL's detection limit if 26Al yield predictions are correct. COMPTEL
Observations of the Vela region have been taken already, with a total of
96 days assembled from 10 pointings altog ether. So far, special pointing
requests had been ignored, however, severely limiting the cumulative sensitivity
due to large off-axis angles. We propose to perform dedicated observations
of the Vela region that minimize possi! ble systematic backgrou
GRO-97-212 DINGUS The highest energy emission
from gamma-ray bursts is very difficult to produce, especially for cosmological
distances. Yet EGRET detects the brightest bursts. The EGRET upper limits
as compared to extrapolations of Comptel spectral fits ar e consistent
with all bursts having high energy emission. The average spectrum from
30 MeV to 10 GeV is fit by a power law of photon index -1.95+-0.25, and
there is no evidence of any high energy cut off. Only 7 bursts have been
detected above 30 MeV; how ever, EGRET has measured fluxes and spectra
for 20 bursts above 1 MeV. Evidence of longer duration emission is seen
in several bursts. Further observations are requested.
GRO-97-105 DIXON We propose to continue our study
of high energy (E>30 MeV) Galactic point and diffuse emission via non-parametric
(model independent) techniques. Non-parametric techniques provide an important
complement to model-based likelihood analyses, yielding detailed spatial
information about the flux distribution, and the potential for unbiased
point source detection. We approach this study with two types of tools:
data denoising, which attempts to remove photon counting noise in favor
of statistic ally significant structure, and image reconstruction, which
additionally tries to estimate the underlying flux distribution by inverting
the instrument response. Further, we continue investigation of the use
of overcomplete basis libraries, which, from ou r work in Cycle 6, show
the potential for separating point and extended components without recourse
to a particular model.
GRO-97-019 DUROUCHOUX GX 339-4 is a unique source,
in that it presents behaviors belonging to both persistent and transient
sources. Based upon our previous GX 339-4 observations, we propose a multi-wavelength
follow up program. BATSE will provide continuous ob servations of the source,
which will be correlated with ground based telescope in visible, mm and
cm wavelengths.
GRO-97-110 ESPOSITO For many years it has been
believed that the acceleration of Galactic cosmic rays is due to the strong
expanding shocks fronts associated with supernovae and supernova remnants.
Analysis of the EGRET data near the Galactic plane has reveal ed that at
least seven supernova remnants are spatially correlated with unidentified
EGRET gamma-ray sources and, of these, four have been shown to be consistent
with a model of gamma-ray emission due to cosmic ray acceleration by supernova
remnants. Thes e four remnants, plus one other, all exhibit 1720 MHz maser
emission(OH) and are of the composite supernova remnant type. However,
statistical limitations preclude unambiguous identification of the unidentified
EGRET gamma-ray sources. We propose for: 1) A Target of Opportunity pointing
of EGRET in the event of a Galactic supernova; 2) Non-exclusive data rights
to 26 supernova remnants.
GRO-97-247 ESPOSITO The supernova rate in starburst
galaxies has been estimated to be on the order of ten to twenty times the
supernova rate in our Galaxy. If the dominant acceleration site of cosmic
rays are supernova remnants then the cosmic ray density in starburst galaxies
should also be proportionally higher. This implies that the diffuse gamma-ray
emission from starburst galaxies can be used to directly estimate the cosmic
ray density in these objects. Data from EGRET gamma-ray observations of
the nearb y starburst galaxies M82 and NGC 253 for CGRO cycles 1 through
4 ( April, 1991 through October, 1995) has been analyzed using point-source
likelihood techniques. The results of this analysis are upper limits due
to low exposure. Further observations of NG C253 and M82 (increasing the
exposure) are required in order to determine the properties of these objects.
GRO-97-135 FINGER We propose a systematic study
of accreting X-ray pulsars using BATSE. The full sky will be monitored
daily for pulsars with spin frequencies in the 2 mHz to 0.5 Hz range. Quick-look
estimates of the fluxes and frequencies for all detectabl e pulsars will
be provided on the world-wide web, and refined measurements will be provided
in updates to the long-term pulsar histories currently available from the
COSSC. We also propose specific studies of the persistent binaries Her
X-1 and OAO 1657-4 15, and studies of transient pulsars. This work will
be carried out as a collaboration between Caltech and BATSE/MSFC pulsar
teams.
GRO-97-189 FINGER An outburst of > 100 MeV
gamma-rays from the accreting binary pulsar Cen X-3 was recently reported
by Vestrand, Sreekumar and Mori. Their epoch-folding analysis, which used
pulse frequency measurements determined by us with BATSE data, sho wed
that the EGRET emission was pulsed. We propose a search in archival EGRET
data for pulsed emission from other accreting pulsars. For this search
we will use pulse timing measurements from BATSE to coherently epoch-fold
the EGRET data. We also propose further study of Cen X-3 to see if additional
detection can be made, and to see if the pulsed emission is correlated
with the torque or flux observed with BATSE.
GRO-97-154 FISHMAN Recent discoveries of extended
x-ray, optical, and radio afterglow emission from GRBs raise the possibility
that higher energy (hard x-ray and gamma ray) afterglow radiation may also
be observable. Relativistic fireball models for GRBs pre dict significant
afterglow emission as the expanding fireball interacts with the surrounding
medium. It is proposed that four rapid re-pointing, target-of-opportunity
observations be made during Cycle 7 of strong GRBs with all instruments
of the Compton O bservatory to test this model and others.
GRO-97-044 GEHRELS The sky maps of the 1809 keV
line emission obtained by COMPTEL have revolutionized our understanding
of the origin of Galactic 26Al. However, a recent measurement performed
by the GRIS spectrometer has revealed the existence of a significa nt fraction
of the 1809 keV line emission that does not appears in the COMPTEL map.
We propose an analysis of the COMPTEL data, taking into account the information
from GRIS, to derive a new 1809 keV map that will better account for the
"missing" flux. GR IS also detected a surprising broadening on
the line which implies that much of the 26Al (>50%) is traveling at
velocities of 500 km s-1. This fast 26Al should produce a latitudinal broadening
of the 1809 keV line emission. We propose to study the origin and location
of this high velocity emission using the new COMPTEL map.
GRO-97-160 GROVE We propose a scheduled, 4-week,
OSSE observation of the Crab Nebula to address the following engineering
and scientific issues: (1) Cross-calibration with COMPTEL, and (2) calibration
of OSSE's pulse-shape discrimination efficiency in the current post-reboost,
high-background conditions; (3) Time variability in the total Crab emission
below 100 keV and above 1 MeV; (4) Hardening of the spectrum of the total
Crab above 1 MeV; (5) Transient narrow lines near 75 keV from the pulsar.
GRO-97-169 GROVE We propose target of opportunity
OSSE observations of bright (exceeding 1 Crab) transient emission from
X-ray pulsars. Through phase-averaged and phase-resolved spectroscopy,
we will address the following issues. (1) Search for complex spe ctral
features, such as cyclotron lines and/or the emergence of an underlying
hard component. (2) Determine the pulsed lightcurves and pulsed fraction
as a function of energy. (3) Determine the spectral and pulse-period evolution
through the peak and deca y portion of an outburst. This is a resubmission
of an expired GRO Cycle 4-6 multiyear proposal that resulted in the discovery
of a 110 keV cyclotron line in A0535+26 and pulsar phase lags durings bursts
of GRO J1744--28.
GRO-97-218 HARMON We propose to continue the capability
developed by our group, the BATSE Earth Occultation Team at the Marshall
Space Flight Center, for the use of BATSE as a hard X-ray/low-energy gamma-ray
all-sky monitor. BATSE is the only current instru ment that can perform
this function. We will: 1) monitor daily the activity of strong sources
in the 20 keV to 1 MeV band; 2) search current and recent data for new
or recurrent transients; 3) develop a source catalog covering the first
5 years of occulta tion monitoring; 4) implement a Galactic plane imaging
survey; 5) expand access to Earth occultation monitoring data for the astronomical
community through the WWW; and 6) focus scientific efforts on the analysis
of a sample of objects we detect using our occultation technique.
GRO-97-043 HARTMAN In order to improve our understanding
of the physical processes in blazar jets, which can produce the large observed
luminosities of high-energy gamma rays, we propose to implement Targets
of Opportunity (ToO's) to observe gamma-ray emissi on correlated with exceptionally
bright emission in lower frequency bands. The objects selected for consideration
either have demonstrated previous bright flares in high-energy gamma rays,
or are EGRET-detected and well-monitored at lower frequencies. A t rigger
for a ToO could arise from an exceptionally bright and rising state in
the optical, IR, or mm/submm band. In addition, we propose that a ToO extension
be added to any CGRO blazar observation (regardless of PI) which shows
the object to be in a very high gamma-ray state.
GRO-97-018 HARTMANN The first six years of observations
by BATSE strongly indicated a cosmological origin of gamma-ray bursts (GRBs).
This distance scale has now been demonstrated by a redshift measurement
of an optical transient discovered through the accura te X-ray localization
of GRB970508 by BeppoSAX. We propose the next step, to further support
the distance scale to GRBs by searching for large scale cosmological structures
in the large BATSE database. We consider angular and brightness studies.
A specifi c high school outreach program would accompany this research
effort.
GRO-97-046 HOEFLICH Observations of Type Ia supernovae
prior to maximum optical light in the Virgo Cluster can provide a rigorous
test of sub-Chandrasekhar models in which an outer layer of helium ignites
giving rise to an early intense signal of Ni-56 lines at 0.74 and 0.81
MeV. This translates into one TOO per approximately 3 years. Early detection
is critical for this test. Methods to enable the early triggering and to
optimize the data collection and analysis are presented.
GRO-97-077 HURLEY Many more counterparts may be
needed to obtain a coherent picture of GRBs in the post-BeppoSAX era. To
facilitate this, we propose to reduce the sizes of about 80 BATSE burst
error circles/year by up to two orders of magnitude by triangula tion with
Ulysses, and send the results to the wide astronomical community via BACODINE.
We will also triangulate a subset of about 30 strong bursts/year in a completely
automated mode, with no operator intervention, with delays as small as
half a day. Th e error boxes will be used for a wide variety of projects,
from counterpart searches to statistical studies. Finally, we will augment
the network by adding the NEAR spacecraft, which should yield a subset
of about 50 bursts/year with 1'x10' error boxes. T he above-average estimated
cost is due to the fact that this effort directly supports a large number
of auxiliary investigations. It is, however, heavily leveraged by JPL support
for Ulysses operations. This is a multi-year pr! oposal.
GRO-97-073 IYUDIN The COMPTEL telescope on board
the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray
line sources in the MeV region at a sensitivity of about $10^{-5}$ photons/(cm$^2$s).
Among such line emission sources of interest an i mportant place is occupied
by the classical nova, which could produce astrophysically significant
fluxes of the \na decay $\gamma$-ray line at 1.275 MeV. The nova shell
expelled by the thermonuclear runaway should be transparent to 1.275 MeV
emission a fe w days after the nova explosion. On the basis of Phase 1
and 2 data COMPTEL derived an average 2 \sig upper limit for any neon-type
novae in the Galactic disk of the order of 3 $\times$ $10^{-5}$ \cms (Iyudin
et al. 1995). We are shure that we could do be tter, and for that reason
we would like to propose ToO observations with COMPTEL for any classical
nova with the distance $\le$1 kpc from the Sun, or with the visual magnitude
m$_V$ $\le$4.0.
GRO-97-216 JOHNSON We propose scheduled OSSE observations
of four blazars, and Target of Opportunity pointings in support of the
EGRET multi-wavelength target of opportunity blazar investigations. Of
the four scheduled pointings, we propose observations of P KS 0528+134
and 3C 279 in conjunction with the EGRET multiwavelength campaign for these
objects and propose scheduled observations of PKS 0208 - 512 and 3C 273.
Blazar observations in the OSSE and COMPTEL energy ranges provide the most
compelling argument s for beaming from the gamma-ray observations, test
models which predict the range of breaks in the spectra and the shape of
the spectrum below the break, and test whether soft gamma rays lag or lead
the harder gamma rays.
GRO-97-243 JOHNSON We propose multiwavelength
X-ray/gamma-ray campaigns for IC 4329A and NGC4388, two archetypical gamma-ray
- bright Seyferts of type 1 and 2, respectively, and for NGC 4151, the
brightest radio-quiet Seyfert (type 1.5). The determination of their X-ray/gamma-ray
spectra will test the unified AGN model (Antonucci 1993 and references
therein), according to which Seyfert 1.5s and 2s contain the same intrinsic
X-gamma sources as Seyfert 1s but which are seen through an optically thick
obscuring torus (e.g., Krolik and Begelman 1988). The obtained spectra
will then allow us to study the physical processes responsible for the
emission as well as the contributions of Seyfert 1s and 2s to the cosmic
X-ray background. The OSSE observations will be a ccompanied by simultaneous
observations by XTE and ASCA, which will allow a determination of their
X-ray spectra.
GRO-97-034 KAARET Transient episodes of hard X-ray
emission from several X-ray bursters have been recently discovered. Hard
X-ray emission is an effective diagnostic of thermal and non-thermal processes
occurring in accretion disks surrounding weakly magnet ized neutron stars.
We propose a target of opportunity observation using OSSE triggered by
BATSE detection of a hard X-ray transient from one of five selected X-ray
bursters. The OSSE observations will accurately measure the hard part of
the spectrum (100 -400 keV) and place strong constraints on theoretical
models of hard X-ray emission. This proposal complements our ongoing investigation
of bursters with BATSE and a similar TOO program approved for XTE.
GRO-97-098 KANBACH Several unidentified EGRET
sources are found with spectral and long term temporal characteristics
that resemble those of middle-aged pulsars. Multiwavelength investigations
of selected sources (X-ray, radio and optical) reinforce the impre ssion
that they are gamma ray pulsars. The nature of these candidates will only
be revealed in the future, either through ongoing identification efforts
or ultimately through sensitive measurements with the next generation of
gamma-ray telescopes. It is t hen of great importance to establish accurate
pulsar ephemerides and parameters (eg. age, braking index)using in retrospect
the EGRET database. This will only be possible if we maintain a regular
sampling of the candidate sources over the times until the objects are
identified. We propose to monitor the prime candidates during 1998 to secure
the data for future pulsar analyses.
GRO-97-237 KINZER Measurement of the cosmic diffuse
gamma-ray background (CGB) is one of the original proposed science goals
of OSSE. OSSE provides a capability, unique now and into the forseeable
future, to observe this fundamentally important radiation. F ailure to
seize the opportunity to use this capability to measure the spectrum and
the isotropy of the CGB would be a considerable loss to astrophysics. Brief
proof-of-concept tests with OSSE show quite encouraging results. OSSE will
be able to confirm an d possibly extend the spectrum in the 50 keV to one
MeV range, and to measure any spatial anisotropy in the CGB with a potential
sensitivity more than an order of magnitude better than previous work,
and adequate to detect the expected anisotropy. The pro posed observation
program includes pointed observations in 6 roughly orthogonal directions,
two of which are correlated with the cosmic microwave background anisotropy.
GRO-97-238 KINZER Deep OSSE observations of the
inner galactic ridge, configured with the long axis of the collimator parallel
to the plane, have been made only in Phase 1. This type of observations
is essential to understanding the multi-component galactic plane continuum
over the 50 keV to 10 MeV range. The existing sparse set of such observations
provide a much improved understanding of the spectral and spatial details
of this region (e.g. Kinzer et al. 1997a,b,c,). However, many questions
are raised by these results which can be answered by deeper collimator-aligned
observations. Understanding the several spectral components, which follow
two or more different longitude distributions, requires a systematic study
of the galactic ridge in both longitude a nd latitude. The requested observations
will reasonably complete the on-going multi-year positive longitude observation
program for the inner galaxy at 0 deg. latitude, and will complete roughly
25% of on-going multi-year obse! rvation program.
GRO-97-039 KIPPEN An outstanding problem in gamma-ray
burst research is the small number of well-localized events. As a result,
little is known about the small-scale angular distribution of sources.
We propose to accumulate a catalog of more than 500 burst locations, with
total "error boxes" < 1 square degree in area, by combining
BATSE measurements with Compton/Ulysses timing annuli. The large number
and superior accuracy of the combined BATSE/Ulysses locations will allow
us to investigate small-angle clus tering (either intrinsic or due to repeating
sources) and to search for correlations with catalogs of known objects
(e.g., distant galaxies and quasars) with substantially improved sensitivity
over any previous, current or planned efforts. In the absence of significant
self-clustering or galaxy correlations, we will be able to place constraining
limits on burst recurrence scenarios (including time-dependent repetition)
and limit the range of possible cosmological source distan! ces.
GRO-97-054 KIPPEN Years of BATSE observations,
combined with the recent discovery of counterparts related to distant galaxies,
strongly suggest that gamma-ray bursts originate at cosmological distances.
Cosmological burst emission models share the common fe ature that they
are highly constrained by the spectral and temporal properties of high-energy
(~1 MeV and above) gamma rays, where relatively little is known. We propose
to use the measurements of BATSE and COMPTEL to investigate in detail the
high-energy component of burst spectra and the short time scales over which
the high-energy flux varies. The advantage of using BATSE measurements
for the bulk of this investigation is that many bursts with high count
rates can be studied. COMPTEL will be used to co nfirm the accuracy of
the BATSE high-energy measurements.
GRO-97-024 KOUVELIOTOU BATSE has produced a unique
database on the bright black-hole candidates Cyg X-1, GX339-4, GRO J0422+32,
GRO J1719-24, and GRO J1655-40; new transient black-hole candidates are
discovered at a rate of about one per year. We propose to cont inue our
successful study of the temporal (fast variability in a frequency domain
of 4mHz to 30 Hz) and spectral (20 to 300 keV) behavior of all these sources
over a wide range of luminosities and spectral states. Motivated by the
fact that the latter thr ee sources are transients, we also propose to
expand this study to include temporal analysis of transient sources detected
with BATSE in the future. Our studies cover an energy range only barely
explored and an unprecedented time span of months to years.
GRO-97-048 KOUVELIOTOU During the first 6 years
of its operation, BATSE detected recurrent emission from two of the three
known SGR sources, SGR 1900+14 (once) and SGR 1806-20 (thrice). The first
reactivation of the latter prompted an immediate, international ca mpaign
resulting in the identification of the X-ray counterpart of the source,
which also coincides with a compact radio source and a rare type of a very
luminous and massive blue star. Its third reactivation initiated a TOO
with RXTE, which resulted in t he first unambiguous detection of "bunching"
in SGR outbursts in the 2-60 keV energy range. We propose to monitor and
analyze SGR emissions for at least 2 years, reconfiguring BATSE to obtain
better sensitivity to SGRs. We expect to enable multiple source identifications
and lead to a better understanding of the SGR population.
GRO-97-147 KUIPER The binary milli-second pulsar
PSR J0218+4232 was detected as a high-energy 5-sigma source in the ROSAT
HRI data. Indications for pulsed emission were seen in these HRI- and in
archival PSPC data. It was noticed by Verbunt et al. (1996) th at an unidentified
EGRET source 2EG J0220+4228 is positionally consistent with the pulsar;
a timing analysis of the >100 MeV data yielded intriguing, but inconclusive
results with pulsed signifances slightly below the 3-sigma level. A similar
timing analy sis using now all available archival EGRET data shows an increased
significance, while a phase resolved spatial analysis in broad energy ranges
above 100 MeV showed a nice ON-OFF effect in the skymaps. So, 2EG J0220+4228
may be the first milli-second puls ar seen at gamma-ray energies, but further
substantiation is needed. Here we ask for a deep EGRET exposure of at least
4 weeks in order to determine the nature of 2EG J220+4228.
GRO-97-190 KUNDU The Sun is an important laboratory
for understanding particle acceleration processes which may operate in
many other astrophysical contexts. Building on our previous research which
has demonstrated that the MeV electrons form a distinct po pulation in
solar flares, we propose to continue to compare data taken with CGRO/BATSE,
which is primarily sensitive to < 200 keV electrons, with images of
very energetic electrons in solar flares obtained using millimeter--interferometer
observations. Th e BATSE data supply the time evolution and the energy
distribution of the (primarily lower--energy) electrons which produce hard
X--rays in solar flares, while the millimeter data supply the same information
for MeV--energy electrons. We will study the pr oduction of MeV--energy
electrons in solar flares and their relationship to the lower--energy electrons
which produce the bulk of the observed hard X--rays, and use the results
to constrain particle acceleration theories.
GRO-97-244 KURFESS A small scan-angle dependent
background systematic effect has been found in the analysis of OSSE data.
The magnitude of this effect is sufficiently small that it does not have
a significant impact for standard OSSE observations which use 4 .5 degree
background offsets. However, it is a consideration for observations which
require larger background offsets (e.g. such as observations of the galactic
plane), mapping observations, and observations which require one-sided
background offsets. The scan-angle dependent background is due to the non-uniform
spacecraft background which is produced by the cosmic ray and trapped particle
environments. Following the recent reboost of GRO from a 425 km orbit to
a 515 km orbit, the trapped proton environme nt from South Atlantic Anomaly
passages has increased by a factor of 3-4. We propose OSSE observations,
using unallocated time in the observing program, to calibrate the scan-angle
dependent effect in the higher background env! ironment.
GRO-97-119 LAMB Studies of the angular distribution
of gamma-ray bursts on small scales can place constraints on repeating
and on the clustering of burst sources (and thus on the distance to the
burst sources, if they are cosmological). Knowledge of burst positions,
and the statistical and systematic errors in them, are crucial to these
studies. We have developed a powerful likelihood method that allows us
to inter-compare burst positions determined by various instruments. We
have used this method to inte r-compare burst positions determined by BATSE
and annuli in the current 3rd IPN catalog, and thereby to estimate the
systematic error in the BATSE burst positions. We will redo our analysis
using annuli in a revised 3rd IPN catalog. We will also inter-com pare
burst positions determined by BATSE, COMPTEL, EGRET, Rossi XTE, WATCH-GRANAT,
and the 3rd IPN.
GRO-97-060 LEISING This is a request for continuation
into Cycle 7 as suggested by the Cycle 6 peer review and endorsed by the
CGRO project. Only 3 weeks were actually scheduled and the first was bumped
for a target of opportunity. We have assembled all nece ssary tools, include
the latest COMPTEL map of 26Al in the region and the ROSAT map of the remnant.
We await our first observations. We strongly request that the full complement
of 10 weeks be carried out. Recognizing the difficulty of scheduling, we
are willing to wait into Cycle 8 for this to be completed. Basically, our
goals were and are to confirm the detection of 26Al emission from the Vela
direction and to determine whether this 26Al is indeed from the Vela supernova
explosion, to extend the measur ement of the compact nebular continuum
to \sim1 MeV, and to improve the measurement of the Vela pulsar light curve
and spectrum.
GRO-97-061 LEISING This multi-year Cycle 4 proposal
was approved through 1999 and rated ``outstanding'' by that peer review.
We resubmit this Target of Opportunity proposal to remind the CGRO project
of the ToO criteria and to request funding if and when the se observations
are carried out. No funding was required at the time of submission, but
it is requested now as direct project funding for science analysis by these
investigators as instrument team members is no longer available. We wish
to keep the ToO cr iteria and requested observations as they originally
were. Briefly, we proposed extensive observations of suitably nearby supernovae
with the OSSE and COMPTEL instruments to further understand the nature
and details of supernovae of Types Ia, II, IIb, and Ib.
GRO-97-062 LEISING This multi-year Cycle 4 proposal
was approved through 1999 and rated ``outstanding'' by that peer review.
We resubmit this Target of Opportunity proposal to remind the CGRO project
of the ToO criteria and to request funding if and when the se observations
are carried out. No funding was required at the time of submission, but
it is requested now as direct project funding for science analysis by these
investigators as instrument team members is no longer available. We wish
to keep the ToO cr iteria and requested observations as they originally
were. Briefly, we propose observations of suitably nearby classical novae
with the OSSE and COMPTEL instruments to clarify the nature of the outbursts
of both carbon-rich and neon-rich types.
GRO-97-187 LIANG In Cycles 4, 5, and 6, we have
been performing spectral fitting and theoretical studies of the SGR bursts,
and multiwavelength observations and modeling of the highly unusual quiescent
counterparts from the millimeter through the infrared. We propose to continue
this program in Cycle 7. We will use the data from the Cycle 6 bursts from
SGR 1806-20 to perform detailed fitting with our Compton and synchrotron
burst models. We request non-exclusive data rights to the BATSE data from
any new b ursts in Cycle 7 from any of the SGR for our burst modeling program.
We have, and/or will shortly obtain, impressive new high resolution near
infrared spectra, complete far infrared spectra, and imaging at a number
of wavelengths that we will use to clari fy the relationship of the multiple
components to the source of the bursts of gamma rays.
GRO-97-208 LIANG This is a Compton Cycle 7 Guest
Investigator proposal for the renewal of Cycle 6 grant NAG 5-3840. It concerns
the modeling, analysis, and interpretation of gamma-ray burst (GRB) continuum
spectral evolution data obtained by BATSE. This pr oject is an ongoing
collaboration between Rice University and the BATSE instrument teams. Following
the major developments of this past year, we will focus in Cycle 7 on spectral
evolution properties that may bear on the multiwavelength (radio to X-ray)
b ehaviors of GRBs and their afterglows, and also put potential constraints
on their emission mechanisms and distance scale. This is the core research
project of the group at Rice.
GRO-97-163 LINGENFELTER We propose to make a thorough
analysis of the new, much more extensive COMPTEL, EGRET and OSSE data from
the Orion-pointed observations of Cycles 5 and 6, using the Monte Carlo
simulation programs,which we used to analyze the earlier data from Phase
1 and Cycle 4. Thorough analysis of this new data is essential in order
to resolve the spacial distribution of the emission region and the spectral
shape of the emission features, which in turn will enable us to much more
tightly constrain the required energy spectrum and abundances of the energetic
particles and also the ambient medium in which they are interacting and
distinguish between possible emission processes and accelerated particle
sources.
GRO-97-252 MACOMB While over 150 sources emit
gamma-rays above 100 MeV, the nature of the gamma-ray sky above 1 GeV is
less well understood. A catalog of gamma-ray sources based on photons with
energies greater than 1 GeV has been developed from 4.5 years o f EGRET
observations. Twenty six sources have identifications with objects seen
at other wavelengths. Thirty are unidentified with nine of the 30 being
new sources. There is some evidence among the unidentified sources for
two luminosity classes. We propo se to extend our study of GeV gamma-ray
sources using further archival EGRET data. A search for transient sources,
variability analysis and spectral studies will be the new emphasis.
GRO-97-123 MALLOZZI The BATSE detectors have recorded
the first observations of an unexplained terrestrial phenomenon: brief,
intense flashes of MeV photons. These events, known as terrestrial gamma-ray
flashes, must originate at altitudes above 30 km to be o bserved by the
orbiting detectors. Approximately 65 events have been observed in the past
six years. The most likely origin of these high-energy photons is bremsstrahlung
from relativistic electrons from high altitude electrical discharges above
thunderst orm regions. We propose to continue observations of temporal
and spectral properties for production and publication of a catalog of
these events. Temporal correlations with radio observations made at Palmer
Station, Antarctica and spatial correlations wit h satellite images of
thunderstorm regions near GRO during these events will be investigated,
enabling verification and testing of proposed theoretical models of the
atmospheric processes believed to be responsible for these u! nique observations.
GRO-97-009 MATTOX We propose to continue our study
of the Geminga pulsar with a cycle 7 exposure. The unique contribution
of Geminga to the study of pulsar emission mechanisms and spin-down demands
ongoing observations by EGRET to refine its pulse ephemeris and improve
the statistics of its pulse profile and phase-resolved spectra. A cycle
7 observation is crucial to a better understanding of the timing noise
behavior of Geminga. This bears upon two very interesting questions: 1.
A braking index of 17 +/- 1 is found through a coherent analysis of the
24 yr baseline provided by EGRET, COS-B, and SAS-2 observations. 2. The
EGRET timing residuals appear to have a sinusoidal modulation that is consistent
with a planet of mass 1.7/sin i M_earth orbiting Geminga at a radius of
3.3 AU. This cycle 7 exposure alone cannot possibly confirm the planetary
hypothesis. However, it could serve to disprove it.
GRO-97-221 MATZ Recent observations of post-burst
soft X-ray emission by BeppoSAX have demonstrated the importance of such
detections both for counterpart searches and for understanding the physics
of GRBs. The rapid decay of the flux (1/t or faster) make s prompt measurements
critical. OSSE has the capability to respond very rapidly (<2 min) to
burst positions calculated by BATSE on-board GRO. This is by far the most
prompt pointed response by a high energy instrument (compares to ~6.5 hrs
minimum with SA X). We propose to continue the operation of the BATSE/OSSE
rapid burst response for 1--2 events/month with at least 12 hr observations
of each burst. This will overlap with any SAX pointed response and is consistent
with the known duration of soft X-ray e mission. A 12 hr slew produces
no significant sensitivity decrease in the scheduled observations and requires
no special or additional mission operations resources. We also propose
to analyze any events serendipitously observe! d in the OSSE FOV.
GRO-97-223 MATZ After six years of successful
operation in orbit, OSSE has surveyed a large fraction of the important
hard X-ray point sources. Most future observations of hard X-ray sources
can now be performed by XTE and SAX, enabling OSSE to be used fo r observations
that it can do uniquely well. One of the most critical of these is the
mapping of diffuse galactic continuum emission. With its high sensitivity
and large but well defined field-of-view, OSSE has the capability of mapping
the diffuse galact ic continuum over the energy range 0.05-1 MeV. Mapping
techniques have been developed and applied to OSSE data which can achieve
resolutions of up to ~1-2 deg. This proposal, a continuation of an approved
Cycle 6 proposal, requests a sequence of observati ons which will be used
to generate maps of the diffuse galactic continuum emission over the longitude
range ~10-55 deg. These observations will provide improved sensitivity
to diffuse emission over all previous and currently p! lanned missions.
GRO-97-220 MCCOLLOUGH We propose coordinated hard/soft
X-ray, IR, and radio observations of the relativistic jet source Cyg X-3
in association with our monitoring and accepted observing programs with
other spacecraft and observatories. Continuous daily monitori ng of Cyg
X-3 has been done for over a decade in the radio and for over 6 years in
the hard X-ray by BATSE on CGRO. Recent studies show a remarkable set of
relationships between the hard X-ray, soft X-ray, and radio which are related
to the formation of r elativistic jets in this system. BATSE LAD occultation
data will be used for the hard X-ray component in this study.
GRO-97-236 MCCOLLOUGH We propose to finish the
survey of the hard x-ray/gamma-ray emission from Supernova Remnants (SNRs)
using BATSE occultation data started in cycle 5 and continued in cycle
6. The ability of BATSE to continuously monitor the entire sky allow s
for a uniform study of a large group of objects measured with the same
instrument and sensitivity. From 45 remnants surveyed 5 are detected and
11 remnants show possible emission and are still being analyzed. When finished
we will have created a hard x- ray/gamma-ray emission catalog of SNRs from
the BATSE data and where possible will differentiate between the various
types of hard x-ray/gamma-ray emission seen from the SNRs. Equally important
will be the establishment of upper limits for SNRs which do n ot show any
emission. Particular effort will be taken to create spectra for the SNRs
detected.
GRO-97-031 MCCONNELL We have recently generated
the first all-sky map at 2.2 MeV using COMPTEL data from the first five
years of the CGRO mission. The purpose of this effort was to search for
sources of unshifted neutron capture radiation, as one might expect in
certain binary accretion scenarios. Although generally featureless, the
maps do show one point-like feature (provisionally designated as GRO J0332-87)
at a significance level of ~4 sigma. There is no obvious counterpart to
this source, based on standar d scenarios for 2.2 MeV emission. We therefore
propose to obtain further observations to confirm the presence of this
source using both OSSE and COMPTEL during cycle 7. In parallel with this
effort, we also propose to continue work using archival COMPTEL data to
refine our 2.2 MeV analysis methods (especially with regards to background
modeling) and to incorporate additional data from later observations not
included in the present analysis.
GRO-97-072 MCCONNELL Although observations of
soft X-ray transients with CGRO have provided a wealth of information about
the hard X-ray emission of these sources, observations of spectra near
1 MeV are limited. Based on experience with Cyg X-1, such observati ons
would be valuable in our efforts to understand the high energy spectrum.
Even a single significant datapoint near 1 MeV, when combined with lower
energy data, could prove useful (c.f., GRO J0422+32). COMPTEL is capable
of providing such data. Unfortun ately, past COMPTEL observations of XRTs
are limited in number, and often so limited in exposure that no detection
was possible. We propose long exposure observations with COMPTEL (perhaps
in a low threshold mode) of any new XRT which becomes visible duri ng cycle
7 and which is likely to be detected by COMPTEL. We also propose to continue
the analysis of archival COMPTEL data incorporating recent improvements
in data analysis, especially with regards to spatial structures in t! he
data.
GRO-97-053 MESZAROS Progress in understanding
Gamma Ray Bursts is crucially dependent upon a close interplay between
increasingly specific analyses of the data, including new multiwavelength
observations, and increasingly realistic physical models which addre ss
these data. We propose to calculate the spectral variability of internal
shock models of GRB, and to compare the calculated light curves and spectral/temporal
correlations with the available gamma-ray data. Building upon our succesfull
fireball aftergl ow model, we will also follow the development of the fireball
into its late stages, up to months after the event, and investigate the
time behavior and variability of the emission at X-ray, optical and radio
wavelengths. The predicted observational signat ures will be contrasted
to the data from the various relevant experiments.
GRO-97-078 MITROFANOV We propose a large project
to perform comprehensive studies of generic signatures of flux and energy
spectral variability of gamma-ray bursts from the 4B and later BATSE data
bases. The basic signatures will include the Average Emissivity Curves,
Average Normalized Profiles and Average Energy Spectra both for the total
burst sample and for different sub-samples selected by peak flux or duration.
These signatures will be compared among the various samples to resolve
any significant differen ces between them. Monte Carlo modeling will be
used to exclude any biases from the average signatures and to make robust
estimations of the significance of differences between them. Both model
independent and model dependent transformations will be develo ped and
applied to the observed signatures of bursts in order to characterize the
"typical emission" in the co-moving frames of their emitting
sources. Any effects requiring distance-dependent source evolution will
be identifi! ed.
GRO-97-014 MUCH A prerequisite for a broad energy
study with CGRO is the assessment of the absolute calibration uncertainty
of the CGRO instruments or at least relative calibration between the instruments.
A cross calibration of the instruments can be per formed by selecting suitable
objects on the sky. Experience from previous analysis has shown that a
dedicated calibration observation is required for this purpose. Therefore
we propose a 4 week Crab observation where instrument configuration and
pointing direction is optimized to allow proper cross calibration. This
observation will help to resolve the inconsistency in the OSSE-COMPTEL
cross calibration above 1 MeV. It is emphasized that instrument calibration
issues, and therefore the results of this ana lysis, can impact many scientific
conclusions.
GRO-97-049 MUKHERJEE We propose to carry out observations
of PKS 0528+134 with EGRET, correlated with observations at longer wavelengths,
to examine short time scale variations (1 to 3 days), which can be detected
by EGRET only during bright flares. Such multi wavelength studies will
help us to understand better the processes by which gamma-rays are produced
in blazars. PKS 0528+134 has shown one of the highest fluxes in previous
EGRET observations and exhibits extreme variations in its flux history.
In the 199 3 March observations, PKS 0528+134 was seen to flare in gamma-rays
by EGRET, with a flux level that was comparable to the Crab pulsar. We
also propose to study the correlation between the spectral index and the
flux of PKS 0528+134, during a flare.
GRO-97-176 MURPHY We have applied new techniques
for analyzing intense solar flares to the OSSE data obtained from the 1991
June 4 solar flare to obtain new information about the accelerated-particle
spectra and composition and about the ambient plasma at t he flare site.
We propose to apply these same techniques to the three other large 1991
June flares that were well-observed by OSSE (June 6, 9 and 11) and, if
funding permits, to other weaker flares. Among the specific areas of analysis
we wish to study ar e: continuous ion acceleration vs. trapping; accelerated-particle
composition, spectrum and directionality; electron vs. ion energetics;
temporal variability of the ambient material composition; the photospheric
3He/H ratio; existence of pre- and post-fla re energetic ions; and flare-plasma
temperature and density as deduced from the positron annihilation line
and 3-gamma continuum.
GRO-97-005 NEMIROFF All known types of objects
at cosmological distances have been seen to undergo a gravitational lens
effect except GRBs. Given even conservative cosmological distance estimates
for about 2100 BATSE detected GRBs through Cycle 7, there is ab out a 25
percent chance of finding a gravitational lens effect caused by the known
galaxy field. Precise timing information for GRBs carries enhanced information
about the lens masses as well as general cosmological parameters. Our search
for lensing, how ever, also encompasses a search for a cosmological abundance
of dark matter from the scale of 1E-15 to 1E9 solar masses, including a
planetary mass range unavailable to other methods. Previous CGRO lens searches
led by the PI have yielded interesting publ ished limits and software that
can be used in a Cycle 7 search. In addition to continuing past searches,
we propose adding a ``real time" search designed to catch lens candidates
within a week of being detected.
GRO-97-125 NOLAN The unidentified EGRET source
2EG J1835+5919 is bright and well localized. There is no convincing evidence
for variability. It has never been observed well by EGRET. We propose further
observations to settle the issue of variability, to im prove the search
for pulsations, and to archive data in case it is discovered to be a pulsar
by observations in another wavelength band.
GRO-97-082 NORRIS Recent detections of apparent
gamma-ray burst (GRB) counterparts in optical and radio wavebands strongly
favor the cosmological distance scale, at least for some GRBs, opening
the possibility of GRBs serving as cosmological probes. But: GR Bs manifest
great diversity; moreover, there are the possibilities of a luminosity
distribution and evolution of average GRB characteristics with cosmic time.
Given the sparse information at longer wavelengths for some time into the
future, the ONLY viabl e approach to constraining GRB diversity, e.g.,
as a function of peak flux, necessarily involves use of GRB data. We will
address the fundamental question of degree of GRB (non)uniformity by applying
our automated pulse-fitting algorithm to determine micr o and macro GRB
temporal/spectral characteristics as a function of GRB peak flux, thereby
constraining the use of GRBs as cosmological probes.
GRO-97-150 OTTERBEIN We propose to observe the
ultraluminous blazar S5 0836+710 with EGRET in the gamma-ray regime and
at other wavelengths. S5 0836+710 shows pronounced outbursts of its flux
in the high energy regime (optical/x-rays/gamma-rays) most probably related
to variations at lower frequencies (radio/mm) and to the ejection of new
jet components. In addition, short term gamma-ray variability is indicated
during states of lower activity. Previous multifrequency studies of blazars
showed that a variety o f quite different models is capable to explain
the overall spectrum of the objects. Crucial tests to these models ask
for time delay mapping of the outbursts throughout the spectrum. Dense
sampled observatons in frequency and time settle stringent constra ints
on the models.
GRO-97-199 PACIESAS We propose to produce a comprehensive
set of catalogs of BATSE gamma-ray burst spectra that will be of general
use to the astrophysical community. The catalogs will make use of the wide
range of BATSE data types and allow convenient access to deconvolved spectra
and corresponding model functional fit parameters with various combinations
of time and energy resolution. The catalogs will be made conveniently accessible
via the World Wide Web and will be updated regularly as new burst data
com e in.
GRO-97-183 PARK We propose to search for simultaneous
gamma-ray burst(GRB) optical counterparts using a wide-field-of-view telescope
system that is connected to the Gamma-ray Coordinate Network (GCN). LOTIS
(Livermore Optical Transient Imaging System) is an automated telescope
system that views a 17.6 x 17.6 deg field of view, is sensitive to Mv ~14
and responds to a burst trigger within 10 sec. The system has been operating
since Oct. 1996 and has recorded many GCN triggers, some while the bursts
were st ill in progress. We propose to further enhance this system to be
sensitive to Mv ~ 16 and construct a 50 cm aperture system that matches
the new GCN notices with smaller errors (LOCBURST and RXTE triggers). A
simultaneous detection and the production of t he realtime GRB light curves
will greatly enhance our understanding of GRB physics.
GRO-97-121 PENDLETON Recently we have identified
two types of pulses in gamma-ray bursts (GRBs) that exhibit significantly
different luminosities. Emission pulses in GRBs that show a marked lack
of fluence above 300 keV appear to be 10 times less luminous than emission
pulses with high energy flux. Some bursts show both types of pulses indicating
that one source object is capable of producing both types of emission.
We propose to perform detailed studies of the admixture of these pulses
in GRBs to refine our a bility to detect cosmological signatures in the
burst data, and to provide observational characterization of GRB emission
that will be important for theoretical modeling.
GRO-97-126 PENDLETON Recent developments in burst
counterpart identification makes the rapid production and distribution
of accurate burst locations particularly important. We propose to implement
some of the location algorithms from the Hunstville location co de LOCBURST
in the BACODINE location code so that locations with 2 degree accuracy
can be produced within 10-20s of the burst trigger for around 30 bursts
per year. These locations will allow automated search projects to perform
deep searches of burst loc ations at other wavelengths while the longer
bursts are still in progress.
GRO-97-202 PERLMUTTER Despite reports of gamma-ray
burst (GRB) related optical transients (OTs), the origin of GRBs remains
unknown. To understand the physics of GRBs, further observations by all
types of instruments are indicated, requiring rapid, accurate GRB positions.
This project probes a new region of parameter space in the search for GRB
images and positions by making sensitive (V>17.7 mag in 10 sec) optical
measurements during gamma-ray emission and after. Our instrument, the Automated
Patrol Telescope (APT; a wide-field, rapid pointing, 0.5 m aperture, CCD
instrument), has already responded to GRBs 970326.6 and 970329. On receipt
of a BACODINE alert, the APT interrupts its observations and acquires images
starting ~ 20 sec after the GRB trigger. Rapid, automated reduction provides
OT coordinates up to several hours before Sax, increasing critical setup
time for other specialized observations, and providing independent alerts
to compliment and verify Sax results.
GRO-97-036 PETROSIAN We propose to test the cosmological
models for GRBs using their logN-logS relation and distributions of durations
and spectra. Most previous analyses have dealt with some measure of peak
flux, but models and recent multiwavelength observat ions indicate that
the fluence is a more fundamental parameter. We have developed methods
to account for the detection bias of BATSE fluences. We propose to compare
the LogN-LogS distributions of the peak flux and the fluence and their
correlations with b urst duration and spectrum. Our preliminary results
show some paradoxical behaviors and indicate that by this method, especially
with the inclusion of spectral biases and dispersions, we can provide answers
to some important question: Is the total energy or the peak luminosity
a standard candle? What are the relations of this standard with the durations
and spectra? Are there two populations of GRBs with different durations
and spectra?
GRO-97-087 PETROSIAN We propose to analyze BATSE
and EGRET data on solar flares to test the stochastic acceleration model
of the the impulsive phase, where plasma waves or turbulence arising from
the energy release process play a major role. We have shown that this model
can explain the details of the spectral deviations from a simple power
law of two electron dominated flare. The scattering by the turbulence can
also trap the particles in the acceleration region giving rise to bremsstrahlung
X-rays observed b y YOHKOH from these regions. Combining these observations,
not necessarily on the same flares, we can further constrain the model.
We also propose to use the same model for acceleration of protons and compare
the combined bremsstrahlung and nuclear line e mission spectra observations
when the emission is not dominated by electrons. The large dynamic range
provided by combined BATSE and EGRET data is crucial and can provide strong
constraints on the model parameters.
GRO-97-168 PHLIPS We propose a target of opportunity
observation of Cygnus X-1 with OSSE and COMPTEL when it becomes very weak
as measured with BATSE, while at the same time not increasing its low energy
X-ray flux, as measured by the All Sky Monitor (ASM) on RXTE. We consider
this to be the definition of the state of Cygnus X-1 when enhanced MeV
emission was detected during the HEAO-3 mission. Until the launch of RXTE,
there was no way to differentiate between the source going in the known
X-ray high, gamm a ray low state, and a potential rare state of X-ray low,
gamma ray low emission. The observation would be contemporaneous with an
XTE target of opportunity observation and possibly USA observations. The
primary goal of this proposal is to confirm the exi stence of the MeV emission
if the source goes in the defined state. By acquiring simultaneous spectra
over the X-ray and gamma ray band, a data set would be available to test
models of MeV emission and other black-hole models.!
GRO-97-111 PREECE Roughly 15% of bright gamma-ray
bursts exhibit excess low-energy emission, based upon spectral fits of
time-averaged BATSE Spectroscopy Detector data. We propose to determine
the detailed time behavior of this excess. This can be done with BATSE
archival and Cycle 7 data, by performing a series of spectral fits throughout
the time history of bursts showing an excess. We wish to determine whether
or not the X-ray component exists independently of the gamma-ray spectral
history. The answer t o this question has direct bearing on the verification
of theoretical burst emission mechanisms that have been recently proposed.
GRO-97-209 PURCELL OSSE is the only operating
satellite instrument with the capability for studying the detailed distribution
of galactic positron annihilation radiation. Recently, an asymmetry in
the latitude distribution of the 511 keV line has been report ed based
on mapping and modeling results using data from OSSE, SMM and TGRS. This
exciting result, which was the product of a multiyear effort to develop
mapping capabilities using the OSSE instrument, shows an enhancement of
511 keV line emission extendi ng up to ~7-10 deg above the GC. Another
weak enhancement near (-9,-5) is also suggested. A better determination
of the positron source requires an improved understanding of the distribution
of the annihilation radiation. The proposed observations will: 1 ) better
determine the size, shape, centroid and flux of the nuclear bulge component,
2) constrain the latitude width of the plane component, 3) more optimally
study the latitude asymmetry, and 4) improve the sensitivity to ot! her
enhancements.
GRO-97-214 PURCELL OSSE is the only operating
satellite instrument with the capability for studying the detailed distribution
of galactic positron annihilation radiation. Recently, an asymmetry in
the latitude distribution of the 511 keV line has been report ed based
on mapping and modeling results using data from OSSE, SMM and TGRS. This
result, which was the product of a multiyear effort to develop mapping
capabilities using the OSSE instrument, shows an enhancement of 511 keV
line emission extending up to ~7 10 deg above the GC. The exact morphology
of this ''fountain'' is not yet known and it is not clear if this feature
is directly associated with activity in the GC region, although it is interesting
to note that similar asymmetries are seen in radio map s. The proposed
observations will: 1) better determine the location, morphology and flux
of the enhancement, 2) provide a dataset from which a spectrum of the enhancement
can be generated, and 3) significantly improve on curre! nt maps of the
GC region.|
GRO-97-113 RAMATY We propose a new determination
of the photospheric He-3/H based on the time dependencies of the 2.223
MeV line and prompt nuclear deexcitation lines. Using this method, the
photospheric He-3 abundance was determined previously from SMM/GRS data.
Since then longer duration and more precise OSSE data became available
from the 1991 June 4 flare. In addition, we have updated the nuclear cross
sections and the Monte-Carlo codes, and placed constraints on the various
factors that could affect th e determination. Our proposed work will lead
to a much more accurate determination of the photospheric He-3 abundance,
greatly improving on the commonly employed approach which assumes that
the photospheric He-3/He-4 equals the solar wind value for this r atio.
The photospheric He-3 abundance is a key parameter in the study of galactic
evolution, and has major implications on cosmological models as well as
on the problems of the solar wind and solar flare particle acceleration.!
GRO-97-213 RAY We propose to make a two-week observation
of the bright, extremely variable, high-mass X-ray binary system 4U 1700-37
with the OSSE instrument. We will conduct simultaneous X-ray observations
with the USA Experiment aboard ARGOS. We will f it the hard X-ray spectrum
above 50 keV to look for a spectral cutoff, absorption lines, and spectral
variability with greater sensitivity and spectral resolution than previous
observations. The concurrent X-ray observations will also make it possible
to measure the temporal correlation between the hard and soft emission
and better distinguish between spectral models. We will also perform a
sensitive search for pulsations taking into account the measured orbital
parameters of the system. We hope to shed s ignificant light on the nature
of the compact object in 4U 1700-37, and the origin of its aperiodic flaring
behavior.
GRO-97-144 ROBINSON We propose coordinated hard/soft
X-ray, IR/optical and radio observations of the Galactic superluminal jet
sources GRS 1915+105 and GRO J1655-40 in association with our accepted
ASCA, HST, ISO, RXTE, SAX, VLA, VLBI and other ground-based p rograms.
Continuous daily monitoring of these sources in radio, soft and hard X-ray
bands has only existed since Nov. 1996 and permits observing outbursts
from their initial states, determined by BATSE and/or radio flares, back
to temporary quiescence. Th ese remarkable objects provide, due to proximity
and much shorter dynamical timescales, relative to AGN, an exceptional
opportunity to study jet formation, ejection and propagation into highly
relativistic jets. As important, these systems provide probes of accretion
and high energy radiation exceptionally close to their suspected black
hole primaries. BATSE LAD occultation data will be used together with near-face-on
pointings of GRS1915+105 to any one of the 8 BATSE SDs.
GRO-97-217 RYAN One of the principlal goals of
the COMPTEL mission is to study the Cosmic Diffuse Gamma Radiation. A preliminary
CDG spectrum has been reported earlier. The preliminary results suggests
a lower spectrum than pre-COMPTEL estimates. Our goal is to derive the
spectrum with finer energy bins and investigate any possible spectral features.
We want to decrease the error bars by analyzing additional data and study
the continuity of the COMPTEL spectrum with higher and lower energies.
GRO-97-227 RYAN We propose to continue and refine
our studies of microflares using BATSE LAD data. We use an automated search
algorithm to detect smallest X-ray bursts. We have searched the archival
data for bursts into 1994. The output of this search is a microflare database
that can be made public. With improvements in our search algorithm and
our choice of selection criteria to exclude spurious events and with the
new result that events are not fully accounted for in the BATSE low-energy
channel (R. Sc hwartz, priv. comm.), we propose to reprocess the entire
BATSE solar microflare database. This will result in a more uniform and
predictable response among detectors to identify solar events and will
also result in a better sensitivity for small flares. I t is important
to start this process soon to catch up before the onset of solar maximum.
GRO-97-063 SCHOENFELDER A principal objective
of the COMPTEL instrument is to study the large-scale Galactic emission,
both diffuse and from discrete sources, and in both continuum and lines.
Full sky images based on Cycle 1-5 data have already shown that the Gal
actic plane is detected with high significance. The accuracy and reliability
of these analyses depend on deep and uniform exposure coverage of the sky.
The combined exposure and quality of data from Cycles 1-6 is extremely
non-uniform even in the Galactic plane, especially considering angles near
enough to the COMPTEL pointing axis which have the best quality for imaging
analysis. We therefore propose a comprehensive set of pointings designed
to yield a minimum effective exposure of 30 days within 20 degr ees of
the Galactic plane for angles up to 25 degrees from the COMPTEL pointing
axis.
GRO-97-177 SHARE One of the most startling discoveries
made by the Compton Observatory has been the detection by COMPTEL of 3
- 7 MeV emission from the Orion Nebula. The emission appears to be spatially
extended and its spectrum suggests some form of broad ened line emission,
especially near 4 MeV. As the implications of this discovery have significant
impact on several areas of astrophysics, it is essential that another experiment
confirm the detection. Previous OSSE limits are consistent with the COMPTEL
fluxes for an extended source. The OSSE spectra also exhibit a weak (1.4
sigma) line feature near 4 MeV with an inferred flux consistent with the
COMPTEL observation. We propose a six-week OSSE exposure for each of the
next three years, concentrating on a broad ridge of emission suggested
by COMPTEL, in order to confirm the emission. We also suggest an alternative,
and possibly more sensitive, approach for detecting the broad 4 MeV line
that can be applied to all observations.!
GRO-97-179 SHARE The Sun is embarked on Cycle
23 and its activity will rise markedly over the next year. OSSE is the
most sensitive spectrometer in orbit for making nuclear line and continuum
measurements. We propose a plan for making comprehensive observa tions
of the Sun during this new Cycle. We propose that OSSE observe the Sun
on the X-axis for all observing periods without an approved X-axis target,
that are compatible with the Z-axis observation. Under this proposal we
anticipate that OSSE will have Solar exposure for up to 30% of the observing
periods in the next few years. We also propose a Solar Target Of Opportunity
with two levels of response: 1. OSSE slews to the Sun in response to a
BATSE Solar trigger when it lies within 15 degrees of the tra ns-scan plane;
2. The Sun becomes an OSSE X-axis target when the probability of a GOES
X-class flare during the next 48 hours exceeds 20%. This is a multi-year
proposal with a cost of up to $70K/year, dependent on the number o! f solar
observations.
GRO-97-012 STEINLE In this joint proposal by all
CGRO instrument teams, a target of opportunity observation lasting four
weeks with all four CGRO instruments is proposed to measure the spectrum
of the nearest active galaxy Centaurus A in a state of strong ga mma-ray
emission. Observations of Cen A in the whole energy range covered by CGRO
at such a historically common, high intensity level, which has not been
observed by CGRO so far, would provide greatly improved observation precision.
They would provide tes ts of hypotheses concerning intensity-dependent
spectral evolution which were advanced to explain the low and intermediate
intensity level observations made so far with CGRO. A similar proposal
had been accepted for Cycle 6, but Cen A did not brighten abo ve the threshold
set.
GRO-97-155 STRICKMAN The presence of a hard X-ray
tail from the bright low-mass X-ray binary Sco~X-1 has long been a source
of controversy. We have recently detected a hard X-ray tail from Sco~X-1
using OSSE on CGRO. We now propose to study the behavior of thi s tail
in more detail with a longer OSSE observation, performed in conjunction
with a multiwavelength campaign. We plan to learn more about the morphology
of hard X-ray variability from Sco X-1 and how it correlates to behavior
at other bands. Using this information, we will interpret the data in the
light of a number of models that currently predict hard X-ray emission
from low-mass X-ray binaries.
GRO-97-153 SVENSSON ASCA observations show that
the Seyfert 2 galaxy, the Circinus galaxy has a very flat 2-10 keV spectrum
indicating a possible dominance of a reflection component. Estimates of
the expected OSSE-flux show that the Circinus galaxy should be at least
as bright as the Seyfert 1 IC 4329A, and possibly as bright as the second
brightest Seyfert, NGC 4945. The Circinus galaxy has never been observed
at energies > 10 keV. Being expected to be one of the brightest Seyferts
in the hard X-ray, this ga laxy lends itself for detailed spectral studies.
We possess unique tools to make physical (rather than empirical modelling)
of broad band X/gamma spectra of Seyferts.
GRO-97-085 TAVANI Recent EGRET detections of unidentified
variable gamma-ray sources near the Galactic plane opened a new field of
investigation. We propose to study new gamma-ray transients with no % apparent
radio-loud blazar-like counterparts (GRTs) loca lized near the Galactic
plane. The nature of these sources (Galactic vs. extragalactic) and the
mechanism of high-energy emission is currently unknown. We request non
exclusive EGRET, COMPTEL and BATSE data rights for all GRTs of gamma-ray
flux above 10** {-6} ph./cm**2/sec within +/- 30 degrees of Galactic latitude,
and exclusive data rights for the first two GRTs in Cycle 7. EGRET quicklook
analysis will be used to trigger rapid follow-up multiwavelength studies.
We will request a GRO TOO observation in case EGRET detects a new GRT of
flux above 2 x 10**{-6} ph./cm**2/sec.
GRO-97-059 THE Cycle 1 to Cycle 3 COMPTEL measurement
has shown that its 1.157 MeV gamma-line sensitivity is 3-4x more sensitive
than the instrument previously used to measure the Galactic Ti44 line flux.
This improved sensitivity means that COMPTEL can probe the decays of Ti44
133 yrs further back in time than the SMM and HEAO 3 or probe distance
2x deeper to put a strong constraint on the analysis of the SN rate and
Ti44 yield. This sensitivity will be further improved with the data from
Cycle 1 to Cyc le 6. We propose to produce the maximum likelihood map of
Ti44 line from Cycle 1-6 COMPTEL archival data and analyze it with Monte
Carlo simulations. Combining this gamma-ray data with the six historic
supernova recorded in the last milenium, the Ti44 yie ld, and the best
available Galactic extinction model, we will be able to produce sets of
parameters that represent the best of the given constraints.
GRO-97-027 THOMPSON In order to extend the life
of EGRET, the gas in the spark chamber was allowed to deteriorate more
than was originally planned for the nominal two year Compton Observatory
mission. Gamma ray events are lost because the pattern recognition software
and analysis rules are not optimized for the poorer quality data. By developing
improved software and changing the rules used by the data analysts, we
can recover a significant fraction of the lost events, allowing improved
statistics for detecti on and study of sources. These changes can help
all users obtain maximum scientific return from the EGRET data.
GRO-97-030 THOMPSON EGRET has measured the high-energy
characteristics(E $>$ 10 MeV) of a number of gamma-ray bursts, principally
those bright bursts appearing in or near the EGRET telescope field of view.
In some cases, the high-energy emission has been obse rved to last as long
or longer than the emission observed by BATSE. EGRET has collected spectra
in the energy range of 1 MeV to 200 MeV that have been combined with observations
from other instruments to yield spectra spanning up to four orders of magnitu
de in energy. We propose to continue analyzing the archival EGRET data
from gamma ray bursts, concentrating on bright bursts far outside the EGRET
field of view.. The 1-200 MeV spectra will be studied for temporal trends
within a burst. This study should double the number of gamma-ray bursts
with measured high-energy emission.
GRO-97-057 TUELLER During a wide FOV (~100 degrees)
drift scan observation on a balloon flight from Alice Springs Australia
in Oct. 1995, the Gamma Ray Imaging Spectrometer (GRIS) detected (4.6 sigma)
a strong source (>1 x 10-3 photons cm-2 s-1) of 511 keV g amma-ray line
radiation from the Galactic plane near 280 longitude. This source has about
the same intensity as the well-known Galactic center source, but it has
not been previously observed. This new configuration of GRIS was designed
to look for edges i n the cosmic diffuse background and provides very limited
information on the position of the source. We propose an OSSE observation
exactly analogous to the succcessful Galactic center mapping campaign of
cycle 6 to map this bump in 511 keV emission from the plane.
GRO-97-253 VALINIA We propose to study the hard
X-ray/soft gamma ray diffuse emission from the galactic plane via simultaneous
RXTE/OSSE observations. The diffuse spectrum of the central region of the
plane (i.e. +/-- 40 deg) in the energy interval 10 keV-10 MeV is not well
understood, and the origin of the emission still remains unknown. Candidate
radiation mechanisms are inverse Compton scattering, non-thermal electron
bremsstrahlung, non-thermal emission from supernova remnant shells, or
even thermal brem sstrahlung from hot plasma. The contribution of each
component still remains uncertain. Via simultaneous observations with RXTE
(fov: 1 deg FWHM), we will be able to subtract sources from OSSE's spectrum.
This will allow us to: 1) simultaneously measure t he diffuse spectrum
from 2 keV to 10 MeV and constrain the power law shape of the continuum
spectrum, 2) set a lower limit to the latitude extension of the emission
in this energy band, and 3) determine the origin of the emiss! ion.
GRO-97-010 VAN PARADIJS We propose to continue
our analysis of the BATSE data base on the Bursting Pulsar GRO J1744-28.
Our results so far include measurements of peak fluxes and fluences for
all ~ 3000 bursts detected during the 1995/6 outburst, determination of
persistent and integrated burst spectra, and a detailed analysis of the
pulse phase delay during these bursts. We propose to extend these analyses
to include the 1996/7 outburst. For the combined data base of ~ 5400 bursts
we propose to examine burst spe ctral evolution, pulse phase spectra, and
irregular variability in the bursts.
GRO-97-013 VAN PARADIJS We propose to make a joint
spectral analysis of GRBs in the BATSE data base (both those triggered
on board, and untriggered bursts found by a later analysis of the BATSE
data base) which are located within the field of view of the SAX WFCs .
The very broad-band spectral coverage obtained this way for for GRBs will
allow us to test physical models of GRB spectra, improve the search for
cyclotron lines by better defining the spectral continuum, and investigate
the relation between the spectra l softening seen in many GRBs and their
recently discovered low-energy afterglow.
GRO-97-025 VAN PARADIJS We propose to continue
our search of the BATSE data base for events that did not lead to an onboard
burst trigger. We have developed a complete off-line trigger search and
analysis system which we have used to examine 580 days of data. We have
submitted to The Astrophysical Journal a manuscript which describes our
procedures and gives results from a search of 345 days of data. T
GRO-97-158 VESTRAND We propose, in collaboration
with the groups operating the three leading TeV gamma-ray telescopes in
the Southern Hemisphere, a campaign to simultaneously observe Cen X-3 in
x-rays and MeV, GeV, and TeV gamma-rays. We request a 3-week EGRE T/COMPTEL
observation of Cen X-3 during late March and early April 1998 in order
to make MeV/GeV gamma-ray measurements simultaneously with scheduled TeV
observations. The broad-band dataset from our campaign will constitute
a unique database for modeling high-energy processes in x-ray binaries
and will have an important impact on our understanding of accretion-powered
pulsars. We also request access to EGRET/COMPTEL data gathered for a list
of likely XRB sources that we have been monitoring since Cycle 4 .
GRO-97-206 VESTRAND We propose EGRET/COMPTEL observations
as part of a campaign, in collaboration with groups operating the leading
TeV gamma-ray telescopes in the Southern Hemisphere, to simultaneously
observe the archetypical x-ray-selected BL Lac, PKS 2155 -304, in MeV/GeV
and TeV gamma-rays. The gamma-ray observations will be supported by simultaneous
satellite observations at x-ray/UV energies and by ground-based observations
at radio, IR, and optical wavelengths. These measurements of PKS 2155-304,
one o f the most well-studied objects in the extragalactic sky at x-ray
and lower energies, will provide a key test of the ``reunification'' hypothesis
for BL Lacs and, given its distance (z=0.116), uniquely probe the intergalactic
infrared radiation field. We also propose new COMPTEL measurements of the
prototype for ``MeV Blazars''---PKS 0208-512. The observations will allow
us test for the 10-30 MeV excess we detected during Cycle 5 and to better
constrain the duty cycle for outb! ursts of MeV emission.
GRO-97-093 VON MONTIGNY We propose to observe
two TeV sources (Mrk~421 and Mrk~501) with the EGRET instrument for three
weeks each and simultaneously with the new generation of \vCerenkov telescopes
as well as with an optical telescope at Calar Alto providing opt ical polarization
measurements. Both sources show a very interesting spectral and temporal
behaviour in the high energy $\gamma$-ray range. From these observations
we expect an improved understanding of the production mechanisms for the
high energy radiat ion from BL Lac objects. The new \vCerenkov telescopes
will have an energy threshold below 50 GeV and should be operational in
early 1998. Therefore, we anticipate good spectral coverage with GeV/TeV
instruments during Cycle 7 of the CGRO mission.
GRO-97-240 WAGNER The optical identification of
gamma-ray bursts discovered by BATSE and reported by BACODINE using the
Lowell Observatory Near-Earth Object Search (LONEOS) 58 cm Schmidt telescope
and mosaic CCD camera is proposed. The LONEOS system images 10 square degrees
of the sky to 22nd magnitude. Images will be obtained to a limiting magnitude
of 22 (2-sigma) and covering 6 x 6 deg centered on the BACODINE position.
Identification of optical counterparts will be based on variability, as
observed prev iously in the transients of GRB 970228 and 970508, by comparison
with images obtained 24-48 hours after the first images. Potential optical
counterparts will be reported back through BACODINE for monitoring and
measurement of their optical light curves. E xtensive ground-based facilites
are available for detailed follow-up studies of LONEOS optical GRB candidates.
GRO-97-112 WASSERMAN The time histories of gamma
ray emission from GRBs and SGRs will be investigated, in particular, to
search for evidence of periodicities in their emission. BATSE Time-Tagged
Event (TTE) data will be used in a Bayesian framework that has be en successfully
applied to X-ray data.
GRO-97-065 WEIDENSPOINTNER A principal goal of
COMPTEL is to study the Cosmic Diffuse Gamma Ray Background (CDG). Knowledge
of the energy spectrum and the spatial inhomogeneity of the CDG may provide
constraints on models that attribute the CDG to a truly diffuse or igin
or to the integrated emission of unresolved point sources. The galactic
north and south pole regions are of prime importance for the analysis of
the inhomogeneity of the CDG because of the low galactic diffuse emission
and the presence of only a few point sources. The exposure coverage of
the galactic south pole region is significantly lower and far more inhomogeneous
than at the galactic north pole. Four observations, with a total duration
of only 8 weeks, would result in a homogeneous exposure cove rage of the
galactic south pole with a depth comparable to that at the galactic north
pole. This would significantly improve the analysis of the inhomogeneity
of the CDG as well as of the galactic diffuse emission.
GRO-97-137 WILSON The value of actively monitoring
the full sky for outbursts of accretion-powered pulsars has been considerable.
During Cycles 1--6 we discovered 4 new accreting pulsars using continuously
available 1.024 s data. We propose to produce and o perate a similar monitor
for sources with ~64ms - 2s pulse periods, by scheduling 31 ms accumulations
which favorably view the galactic plane. Sensitivities of 35 mCrab in 20
-- 50 keV can be obtained for 1/4 of the galactic plane on a daily basis.
Likely objects detectable in this period range are Be-transient systems,
long-period HMXRBs, GRO J1744-28 - like objects, and radio pulsars.
GRO-97-004 WINKLER We propose to analyse and interpret
gamma-ray burst data using both, "single burst detector" data
and "double-scatter" telescope events, from the COMPTEL instrument
on board the Compton GRO. The main goal of our proposal is to continue
our on-going analysis (following accepted Phase III to Cycle 6 proposals)
of the constantly increasing sample of GRB's observed by COMPTEL in the
MeV range. In particular, we propose to study spectral continua, investigate
evidence of their time variability, analyse time histories and derive precise
burst locations. Burst locations will be used to support identification
of counterparts and to investigate the nature of potential repeating sources.
Another important objective is to search the constantly increa sing sample
of spectra for evidence of emission and/or absorption features, and high
energy cut-offs. This search will be performed using data from both modes
(burst detectors and telescope), combined to allow joint fits from ! 300
keV to 30 MeV.
GRO-97-118 ZHANG We propose to renew our cycle
6 proposal, to continue daily monitoring of and searching from the archival
data for the hard X-ray emission from X-ray bursters using BATSE. We have
discovered hard X-ray emission above 50 keV from several X- ray bursters
in the previous cycles. It is now established that X-ray bursters can also
produce hard X-ray emission, strikingly similar to that from black hole
X-ray binaries. Studying the similarities and differences of these two
classes of systems is an integral part of our investigation. We have also
been carrying out correlated investigations with XTE, SAX and OSSE. Our
on-going monitoring program has already triggered our TOO observations
with XTE and SAX. These broad band investigations are expected to improve
significantly our understanding of the nature of hard X-ray emission from
these systems.
GRO-97-MIN KINZER
This is a proposal to use all (or any) of the Cycle 7 Observing Opportunity
viewing periods to significantly improve the rather sparse OSSE
data base for measuring the OSSE detectors' scan-angle
background dependences. This scan-angle background dependence
is an important systematic error for OSSE non-standard observations.
It can be corrected if the energy and angle dependences can be
determined with sufficient accuracy. These correction factors have by now
been determined to first order, but a larger data base,
particularly at scan angles away from the Z axis and the X axis, are critical to accurately determining the
relevant corrections for each detector. Available measurements of this scan
angle dependence are clustered at scan angles around
the X and Z axes because of the standard two-source
observing modes of OSSE. Just a few additional measurments at
angles well-separated from these axes
could make a great improvement in the scan-angle dependence corrections.
These scan-angle dependent background corrections are important
considerations for such high-priority objectives
as mapping the galactic plane, where essentially all of the observations are
non-standard.