[RXTE FAST RESPONSE, Command opportunities Bradt/Marshall?]
11am OPERATIONS: Response to Senior Review budget guidelines,
and plans to reduce operating costs. Swank/Marshall. This shall
be conducted in Executive Session of the committee, due to the
sensitive nature of allocation of funding to those whose positions
may be directly involved.
ATTENDING:
Dan Schwartz SAO das@cfa.harvard.edu
Michael Pelling UCSD mpelling@ucsd.edu
Jean Swank GSFC swank@pcasun1.gsfc.nasa.gov
Fred Lamb UIUC f-lamb@uiuc.edu
Jon Vandegriff HSTX jonv@xpet.stx.com
Evan Smith GSFC esmith@ucephie.gsfc.nasa.gov
Nick White GSFC white@adhoc.gsfc.nasa.gov
Robin Corbet GSFC corbet@gsfc.nasa.gov
Frank Marshall GSFC frank.marshall@gsfc.nasa.gov
David Smith UCB dsmith@ssl.berkeley.edu
Bob Patterer GSFC patterer@troon.gsfc.nasa.gov
Joe Howard GSFC HowardJ@pop500.gsfc.nasa.gov
Tess Jaffe GSFC jaffe@mikyway.gsfc.nasa.gov
Arnold Rots GSFC arots@xebec.gsfc.nasa.gov
Gail Rohrbach GSFC rohrbach@rosserv.gsfc.nasa.gov
Alan Smale GSFC alan@osirus.gsfc.nasa.gov
Jim Lochner GSFC lochner@xeric.gsfc.nasa.gov
Padi Boyd GSFC padi@dragons.gsfc.nasa.gov
Paula Szkody UofW szkody@astro.washington.edu
Kim Weaver JHU Kweaver@pha.jhu.edu
Ed Morgan MIT ehm@space.mit.edu
Keith Jahoda GSFC keith.johoda@gsfc.nasa.gov
Philip Blanco UCSD pblanco@ucsd.edu
Hale Bradt MIT hale@space.mit.edu
Anne Cowley ASU anne.cowley@asu.edu
Alan Levin MIT aml@space.mit.edu
Rick Rothschild UcSD rrothschild@ucsd.edu
Mark H. Finger USRA/MSFC Mark.Finger@msfc.nasa.gov
PROCEEDINGS FOLLOW:
Monday, 15 September, 1997
0905 - Dan Schwartz reviewed the agenda and gave some opening remarks.
He noted that Paul Hertz would arrive after lunch and that Gunter
Riegler would arrive somewhat later.
0909 - Jean Swank - Project Scientist's Overview
Jean noted that Dan Schwartz's chairmanship of this committee is scheduled
to end as of the end of this meeting and that Fred Lamb would be taking
over. Herman Williams will be assigned as the new RXTE mission director,
replacing Kevin Hartnett. Herman has previously worked on SOHO and WIND
and other missions.
Jean noted that some spacecraft "aging" incidents that have occurred and
been accomodated. There have been incidents in which slews have been dis-
abled; however, safehold was not required. The health of PCU5 has worsened
somewhat with an increasing rate of instability events. Calibrations are
improving, but need more work. Operations have been going smoothly, with
few mistakes, mostly ascribable to reduced manpower. She anticipates
further streamlining in the operations area.
Jean presented target statistics on the proposals received in response to
the recent AO. She noted that there are 62 accepted or published papers
credited to XTE observations to date. Jean noted that Padi Boyd has re-
cently joined the GOF. She then gave some highlights of recent scientific
results: Lag times are observed in Cyg X-1. The large range of binary periods
observable with ASM permits exploration of evolution of pulsars. Intermittent
accretion on Be star/pulsar implies an inhomogeneous wind. Pulsars at
fluxes near equilibrium have reduced pulse amplitudes. Some gamma-
ray bursts have 2-10 keV afterglows of 0.5 uJy hours after the burst.
Pulsations have been seen from 2 to 50 keV from the Vela Pulsar. An
accreting intermediate polar has a very small spot emission and, in out-
burst, the flow along the field lines is emphasized. The infrared and
X-rays from 3C273 appear to be basically the same compton scattered com-
ponent. The microquasar GRS1915+105 has x-ray burst followed by infrared
burst, followed by radio, suggesting synchrotron emission by expanding
electron cloud. The crab (33ms) and PSR B1821-24 (3ms) pulsars have x-ray
peaks closed to their Radio peaks.
Jean noted that analyses of many observations have ostensibly been held up
by lack of an adequate background model for PCA, but that this shouldn't be
such a problem now. She commented on TOO observations: The ASM calibration
is working very well now, although there are still problems triggering on
hardness ratio unless the transition is large. There have not been any
large transients recently, although there have been many small bursts (30
mcrab level). Jean feels confident that RXTE can move to a source in <7
hours; however, she is not so certain that this performance can be
maintained after the manpower in operations is reduced. There are currently
1500 Ksec of public TOO observations. RFO's are being conducted to study
background. About 1 per month to each of 5 positions, for a total of about
1 day, is being carried out.
0943 - Fred Lamb - Word from the new chair
Fred thanked Dan for his work running the RXTEUG. He observed that XTE
mission remains unique and that we need to work to get the maximum return.
Many discoveries have already occured and more are expected. The data
are complex and need more work.
Fred feels that the RXTUG's top priority should be the upcoming senior
review. We have a lot of results upon which to build our case; however,
people need to publish results that are not yet written up. The review
has not yet been scheduled. We need to begin preparing the presentation
now. He proposes scheduling the next UG meeting to support preparations
for the senior review
A second issue is how to best operate the mission in the coming period of
reduced funding.
Hale thanks Fred for his enthusiastic work on behalf of the RXTE mission.
0950 - Joe Howard (for Herman Williams) - Spacecraft Status Updates
Two safeholds have occured in the last year, 22 Sept,96 and 14 Jan, 97.
There have also been two "stop slews" due to a Gimbal and Solar Array
Control Electronics (GSACE) failure and an out of limits power supply on
the GSACE. Solar Array degradation has stopped for now due to avoidance
of straighton illumination. However, in and after each safehold the
spacecraft does orient the soalr panels flush to the sun and they do
incur some degradation.
High temperatures on the GSACE should be reduced when GSACE A is turned
off. The ACS bus monitor will warm start the ACS processor more quickly
and avoid going to safehold. The star Tracker long-term patch has been
implemented to re-initialize the catalog. The Solar Array "gentle-motion"
patch is working. A new TPOCC release gives better timing data(8 to 5
usec).
They have received the EUVE automotion system (called APOCC). They are
now operating APOCC in parallel and expect unmanned operations to start
in mid-December. There is no official evaluation as of yet as to how
well the system is working. Dan asked what the expected savings will be?
They expect two people to do the work currently done by eight.
They are planning to rewrite the EEPROM to avoid frequent SW reloads.
They are considering a software change to automate the solar array off-
setting during safehold. It is not clear that this would be cost effective.
Hale asks what projected battery life is? Joe answers that the solar array
is likely to be the ultimate limiting component (decays exponentially once
we have to move more directly onto the sun). Dan asks whether we have a
plan for load-shedding should the solar array problem become acute? Fred
asks what the extrapolated lifetime is? Joe estimates that the present
operating scheme for the solar array should be OK for 2-3 more years, at
which point, power conservation measures may have to be implemented. One
possibility is to conserve heater power by limiting the observation flexi-
bility. It would also be possible to reduce the observing duty cycle.
1019 - Frank Marshall - SOC Director's Overview
The SOF is operating smoothly. Rapid response to GRB has been implemented.
The GOF has supported AO3 with a large number of proposals received.
XSDC forward processing is running well. There are some problems with
data reprocessing.
Frank discussed efforts to implement rapid response to TOOs for purposes of
identifying GRB counterparts. The ability to do this is limited by the
availability of people. The delay is consistantly ~3.2 h. It is possible
to respond this quickly for other sources if we are willing to spend the
resources. Frank feels we can, in principle, further reduce the delay to
~1 hour by deferring production of a new update plan.
Mark Finger asks for details on the origin of delays. Hale notes that ASM
should be able to produce a burst trigger on its own in the future, possibly
giving a position in ~15 min. He wonders whether TDRSS could be managed
more efficiently to reduce the response delay? Should the XTEUG request
support for this? Frank thinks the command uplink delay is the major
limiting factor. Hale thinks that improving the response time could open up
new discovery space. Joe Howard noted that TDRSS is planning to start a
"demand access" service, which is currently in testing, and could reduce
our upload delay times.
XTE has less sensitivity to a burst counterpart(no imaging), so has to get
to the position more quickly. Finger asked whether GRB TOOs are proposal
based. So far, they are public RFO. Would there advantages in having them
proposal based?
1047 - Robin Corbet - Science Operations Report
There are a small number of A01 targets remaining (6 out of 244) Some are
time critical or require coordinated observations or a certain source state.
Remote observing is working well. There have been 74 users averaging 3.2
displays/day for 929 total displays started. Paula Szkody asked whether
short obvervations could be "held" long enough to actually get set up to
monitor them. She has had problems in this regard. The PCA Standard 1
Light Curve is the most popular display.
Robin noted that FITS files are generated for all observations automatically.
He gave a breakdown of user by domain type.
The spacecraft is now operating at 40 Kb/s nominal rate with no overwrite
problems. Robin discussed future automating of the SOF. Monitoring software
is working well now. They are planning to link the monitoring SW to the
paging SW. Robin discussed planned enhancements for remote monitoring. A
new "summary client" is [planned?]. Robin discussed plans for increasing
reliability (e.g. a routine to check that the important SW is actually
running. The most common problem has been recovery from PCU breakdown.
Robin noted a few problems with the spacecraft that have already been
discussed. They hope to operate automated monitoring in parallel at least
for a few months before committing to it.
1102 - Bob Patterer - XSDC Report
Bob described the two concurrent distribution subsystems (reprocessing
and processing). He discussed their strategy to keep up with the inflowing
data. The system is completely automated from receipt of level 0 data
through "pipeline processing".
Forward processing is complete through day 1341 9/3/97 except for a few
large observations. Forward processing takes ~1 week for 30d of FITS data
and runs continuously until caught up. Distribution then takes 2-3 weeks.
Reprocessing is complete through day 791. The reprocessing system (in
place for only 2 weeks) parallels the forward processing pipeline. The
reprocessing rate will be ~1 month of data per month, according to the
present scenario. They are attempting to make the reprocessed data the
ultimate complete version.
Paula Szkody asked when reprocessing will be complete? They estimate that
year 1 reprocessing will be complete in 9 or 10 months. They are considering
buying more tape drives and adding another distribution system (~$50k + 3 mos).
Alternatively, they could hire another data tech, and process requests 24
hrs/day (~$40K). Or, could delay production IT reprocessing tapes (as
discussed with project scientist and SOC manager on 9/10/97). All three
instrument teams agreed that the delay of the production IT reprocessed
tapes was acceptable to them, in order to speed up delivery to users.
Rick Rothschild asked when would reprocessed tapes appear in the third case?
There were further remarks on the XSDC web pages
1125 Alan Smale - GOF Report
Alan noted staffing changes that have occured. Padi Boyd has replaced
Charles Day as a GOF Scientist. Brian Elza has departed and not yet
been replaced. Alan reviewed GOF support of visiting GOs. The GOF can
support 2 visiting GO teams at a time.
Alan noted that the GOF has delivered promised developments of FTOOLS. He
noted, in particular, XSELECT2 improvements.
On the RXTE archive, Alan expects the switchover to the HEASARC to be com-
plete within ~2 weeks. He discussed some of the details associated with
the transition. He also remarked on development of the web pages.
Alan discussed activities in support of AO3. 276 proposals were received
requesting 54e6 sec of observations for an oversubscription factor of 3.9
that is up from 3.0 on AO2. The subject breakdown is similar to the res-
ponses from AO2. The Peer Review will be in Estes Park, Nov 8-10. Alan
noted that AO2 data will become public before AO1 because of extensions
granted to people working on PCU background, etc. He expects renewed
interest in AO1 observations when reprocessed data is available. Also,
improvements in response matrices and calibrtions should give renewed
motivation to work on the data.
Dan asks about AO4? Alan expects its release in early May 98, assuming
the next UG meeting is 1 March. Inputs to Alan can be provided at that
time.
Kim Weaver noted that analysis of faint source data is not possible for many
users within the official 1 year allowed. The committee requested Alan to
inform users that unpublished data need to be accounted (whatever the reason).
1152 Jean - XTE Publicity
Jean noted problems with maintaining interest in public releases if the item
was already released (say locally). The press has a very short attention
span. Fred Lamb observed that hasty, indefensible releases can backfire and
be very counterproductive.
The AAS will decide what will be publicized at the next meeting by the end of
this November. Fred thinks that KHz oscillations and the Black Hole "holy
grail" haven't received proper attention. He thinks we should pursue a single
topic at the HEAD meeting and a different topic at the AAS. It was noted that
special sessions have probably already been organized for those meetings.
Hale relayed advice from Steve Maran. He feels that it is useful to
publicize papers just before they appear on the web. The author is typically
notified a few days in advance of an article appearing in the letters.
Committee discussed strategies for publicizing results. Fred Lamb asked
whether Jean should have some official help in pursuing these publicity
releases.
1215 - Break for lunch
1315 Al Levine - ASM Status
All three SSC's are operating. They need to redo their gain measurements,
although the calibration appears OK from a cursory inspection. SSC #1 gain
is rising by ~9% per year, the other two are stable to within 1% per year.
They also need to redo the calibration of the position readout. It was last
updated in May/June.
On detection of new sources: The best analysis code has now been running for
several months. An email message is sent for >6 or 7 sigma detections (de-
pending on which SSC has triggered) They do get false alarms from background
anomalies. The current code facilitates the recent quick GRB detections and
localization. They are making more reliable GRB identification and localiza-
tion a priority. To do this, they need to reject background anomalies. Their
goal is to be able to identify a new source with an error box within 15 minutes
of receipt of the data. They hope to use PCA and/or HEXTE data to assist in
burst identification. They have identified 14 probable bursts so far, implying
a detection rate of ~10 bursts/year.
Other Issues: A revised rotation planner is being debugged and verified.
There are many calibration issues (not time critical). They are only able
to devote minimal effort to instrument monitoring. Al warned that reductions
in manpower may jeopardize their ability to do many of the support tasks.
1335 Hale Bradt - ASM Operations
Hale described an effect in which the ASM does not view the general direction
of the sun reducing exposure to that portion of the sky. He proposes to
periodically view fields close to the sun to provide more uniform overall
sky coverage. The instrument is switched off when directly on the sun. They
have written planning SW to select and implement such observations. Hale
proposes 88 pointings/year be performed, adding up to ~1% of the mission time
(equivalent to a single ~150Ksec observation). Pointings would be 1/week for
the remainder of this year. Keith Jahoda noted that it may be difficult for
PCA to observe sources that are (necessarily) somewhat close to the sun.
Mark Finger asked whether this coverage problem could be dealt with as part
of the overall timeline development process? Hale requested support from the
user committee to do this. Dan suggests, at least, trying this. There are no
objections to the proposal, so it stands approved.
1402 Rick Rothschild - HEXTE Status
There are no changes in the HEXTE status since the last meeting. It was
discovered that one shield PMT has not worked since launch. Shield PMTs are
redundant, so this effect was not apparent. The HEXTE team has made adjust-
ments to the commanding procedures to avoid "collisions". Alignments have been
rechecked with essentially no change since the initial IOC calibrations.
The HeXTE team is currently analyzing the shape of the collimator response in
an effort to better understand the instrument throughput. They have analyzed
deadtime corrections for all relevant settings of the instrument XULD window
width. The hope is to better understand the normalization of HEXTE spectra
reletive to the PCA. They HEXTE team has also made follow-up measurements of
the pulse shape discrimination rejection efficiency as part of the cross-
calibration effort.
Rick showed results from analysis of long term resolution trending measure-
ments. He also discussed the status of analysis efforts to verify the
performance of the background modulation system. Rick showed plots of
Off-Source Left minus Off-Source Right background spectra as a indication
of the validity of the HEXTE background substraction process. Jean asked
about the open area calibration. Rick estimates that the HEXTE/PCA normali-
zation discrepancy is ~0.66, but that corrections to our response alone are
not likely to entirely explain the problem.
1418 Phil Blanco - HEXTE FTOOLs and Software
The HEXTE team has released Ftools 4.0 including HXTBACK, HXTDEADPHA,
HXTDEADLC, HXTARF, and XTECOL. They have also delivered new versions of
HXTDEAD, HXTARF and HXTLCURV to the GOF for testing.
Efforts are also underway to support "non-standard user configurations,
scripts for bulk processing, and general sub-rocking interval background
subtraction. Phil listed several calibration products currently in work.
The HEXTE response Matrix is valid over the range of energy resolutions
currently observed. The HEXTE team expects to deliver new collimator response
files upon completion of the current analysis.
Regarding activities in the SOC: Functionality has been added to the displays
per duty scientist requests. Have also added a [server extension] for remote
Guest Observer displays. Fixes have been made to mission monitoring to greatly
reduce the incidence of false alarms. The HEXTE team is currently reviewing
the HEXTE default settings. They may reduce the LLD setting from 12 to 10
keV. They are also considering reducing the modulator default frequency
from 1/16s to 1/32s.
1429 Keith Jahoda - PCA Status
Instrument health: TSM triggers are occuring at a consistant rate. The PCU5
trigger rate is catching up with PCU4 (not known why). Keith showed a list of
observations for which one or more detectors was switched off to "rest" the
detectors. They select observations which do not require the full PCA
collecting area. Monitoring campaigns are a particular example of such observa
tions.
Collimator Response: Keith noted that they have collimator calibrations that
are clean to ~1% near the peak and ~3% on the wings. He showed a Sco x-1 scan
that was used to check deadtime correction for sources that give deadtimes in
the 50% range. Keith also showed deadtime analysis for 1744-28 data for
which the deadtime was higher. Keith noted the presence of faint periodicities
,
evident in very long accumulations that are ostensibly due to imperfections in
the deadtime calculation. He also showed spectral residuals at the ~2% level
for a crab fit up to 30 keV. Above that energy, the residuals are ~5%. Keith
noted that observers are going to be systematics limited in many cases and that
we need to consider how to advise users of this. Keith's fitted crab slope is
gamma = 2.19. The 2 to 10 keV flux is 2.39e-8 erg/cm2-s.
Nick White noted that recent analyses of 3C273 data from XTE, ASCA and SAX seem
to give good agreement.
Background: They are modeling particle and activation components of the
PCA background. Keith showed sky and earth viewing spectra that are clearly
different thus indicating that modeling the sky background by viewing the earth
is questionable. He concludes that spectal analysis of faint sources is
starting to be possible. This requires careful data selection relative to SAA,
etc. Rick and Kim will present results tomorrow. Mushotsky has analyzed data
and arrived at conflicting conclusions. [Need techniques in addition to chi2?]
.
People have done analysis of faint source monitoring and achieve 1 sigma = .24
cps for 3 PCUs. Keith discussed the Ginga experience in which they use "signal
free" data to predict the background in the energy range of interest.
1514 Rick Edelson - Background and Weak Sources
Rick showed NGC7469 data indicating that UV and 2-10 keV exhibit simultaneous
variations. He also showed NGC3516 over 3 a month period. The power density
spectrum shows a break toward longer time scales. He notes that the data still
have a problem with the background correction and that he is reluctant to pub-
lish the results for that reason. He also observed that there are no published
RXTE results on faint sources probably due to background subtraction
difficulties. He showed a light curve of NGC 3516 with modeled errors (that
are dominated by background statistics). Rick contends that the "new"
background model doesn't appear to be better in his analyses. He sees 0.2 to
1.0 cps "excursions", correlated over weeks to months, maybe longer. This
background dominates Poisson noise after only 100s. Dan Schwartz suggests that
PDS analysis of the background residuals would be useful to better understand
the effects on source data.
Rick discussed the XTE vs Ginga background models. He noted that the Ginga
team invested a relatively large amount of resources in the background model,
which appears good to ~1%. Al Levine questioned the validity of the background
model over the entire Ginga mission. It was noted that the model became more
refined and precise with time.
Rick Edelson advocates a two-pronged solution: 1) Could do sky chopping to
explicitly measure the background, and/or 2) apply non-SAA constraints to
observations. He requested the committee to endorse more flexibility to do
the background measurements more thoroughly.
There was discussion of what the PCA team is doing and might do to improve the
situation. Dan suggested an iterative approach to improve our understanding
of the background. Ostensibly, an observer could request a "ping-pong" style
observation; however, there is a 1000s minimum observing time per look
direction. Paul Hertz was uncomfortable with burdening guest observers with
the problem of solving the background. Kim Weaver suggests there should be
less pressure to publish these difficult observations too quickly. Paula
Szkody asked whether enough time is being devoted to background observations?
Keith thinks there is enough data to work this problem. Rick Rothschild asked
whether we need more focus on the problem. Fred thinks that we aren't moving
quickly enough on this problem to prepare for the senior review (see further
discussion of the PCA background which took place the next day).
1630 Paul Hertz - HQ News
Headquarters is dominated these days by the pending SMEX selection. They are
also undertaking a review of the grants process chaired by Mary Kicza. One
problem they want to solve is the delay in getting funding to PIs. They are
also re-examing the question of funding ground based telescopes as part of a
space mission science objective. Gunter Riegler is collecting opinions on this
topic.
XTE is going to be moving into its extended mission phase next year. There
are three important areas to pursue: 1) Senior Review, 2) NASA Management (eg
Huntress, and 3), the Press. Paul thinks AXAF is likely to dominate x-ray
astronomy in the next few years. Paul appeals for people to send copies of
press releases to his area. He needs a PowerPoint slide placed in Gunter's ftp
area each month to maintain visability. ACTION? Hale suggests we may need a
"press officer" to deal with these publicity issues.
Paul also noted that he needs inputs for an Alan Bunner level presentation.
He is putting this together for an October presentation . He needs "real
physics" inputs to support this. Bunner gets 10 minutes out of the entire
4 hour meeting.
Senior review: 8 missions will be competing, including ASCA, ROSAT and
GRO. He advises not criticizing other missions. Better to talk about
complementarity and synergism. It is important to generate papers, especially
in the next six months as a measure of scientific productivity. This is why
Paul is distressed that results are being held up to develop better background
models. He poses the question whether we are delivering the science promised a
t
the last senior review. If not, why? AGNs are not the only XTE science, but
they are relatively cross disciplinary. Paula Szkody was on the review panel
last year, and notes the perception that XTE is primarily a QSO mission. She
commented that the committee looked at the uniqueness of each mission, and
also at the breadth of science it was doing. Paul reminds us that this UG has
the responsibility to advise HQ about how to solve the "weak source" or
background problem. Ed Morgan thinks the AO3 proposals are scientifically much
stronger than the earlier two.
Alan Bunner, Lou Kaluzienski and others at HQ extent thanks to Dan Schwartz for
his stewardship of this committee.
Paul noted that cycle3 is last one for which funding will be granted at the
time observations are selected. For cycle4, XTE will be rolled into the same
pot with ASCA and ROSAT funding of archival analyses. Paul is soliciting ideas
on how to best implement this program. There was considerable discussion of
this. Dan noted that this was discussed at the last UG meeting and that a
letter was written. The key point was that we wanted to avoid having the
proposer write two proposals. It was also important to have the same reviewers
make funding judgements as selection of observations. Guenter Riegler noted
that the rationale for pooling DA funds was to encourage broader,cross-
disciplinary investigations as well as to make a larger pool from which the
best science could be funded.
Guenter noted that the SScAC committee recommended rebalancing funding between
MO&DA and R&A within NASA, but he feels that community will not support such
reallocation.
What is position of the UG on the question of pooling vs separating the funds
for archival vs new data analysis? It appears that we need to reconsider our
letter from the last meeting.
1824 Gunter - On the Senior Review
The review process is being extended beyond Astrophysics; however,
Astrophysics will be reviewed (bi-annually) by itself. One complaint is that
the "missions only" focus was too narrow. There is a question as to whether
the broader grants programs (and currently fenced-off programs) should be
within the scope of the review. Guenter is asking our opinion on what the
ground rules should be.
Guenter offered some general comments. Various disciplines have different
patterns. Planetary missions ask for extensions on the basis of new science.
The Sun-Earth Connection program looks at a mix of older missions plus new
missions to view next solar cycle. Astrophysics tends to look like "more of
the same" i.e. we continue to solve the same problems. Guenter also suggests
publicizing results better. By comparison, Guenter sees a continuous flow of
results from SEC, Hubble, etc.
16 Sept - Reconvene
0905 Dan - Reviews agenda
0905 Kim Weaver - Seyfert Reflection Components and Comments as a User
Kim feels that the response matrix and background model are steadily improving;
however, the time scale for development of the background model is longer than
we hoped. She comments that not all PIs are as experienced in recognizing
the limitations of the background model. She notes her experience that results
already presented at the June meeting have changed as a result of changes in
the background model.
Kim discussed her Seyfert observations, in particular detecting a reflection
component in 9MCG-5-23-16 (a Seyfert 1.9 galaxy). She noted that questions
remain about the cross-calibration with ASCA. She observed that her data are
extremely systematics limited and that the "background model is not working".
This talk is about the background model in use as of June (which appeared to
work OK). She measures the column density from ASCA data. She is experi-
menting with two different response matrices (M8 and M85). This source is the
5th brightest seyfert in x-rays. She is examining the question of whether the
iron line is broadened. There is an intense iron line evident in residuals to
a power law fit. The equivalent width of the line is not very dependent on
the details of the continuum fit. The fit for a reflection + narrow gaussian
model does appear to depend on which response matrix is used. She showed
residuals for various models. A reflection + broad gaussian model gives the
best looking residuals. She characterizes this observations as the first clear
detection of reflection in MCG-5-23-16 and independent confirmation of a
gravitationally broadened Fe Kalpha line. She concludes theta=81 deg (edge-on)
.
Jean observes that an errant gain could lead to error in the power law index.
0932 Rick - Cen A Reflection Component
This was a short (10ksec) observation. Cen A is one of closest and brightest
AGNs. Rick referenced Kim's cartoon of the source configuration; however, in
this case there is a collimated jet. The spectrum has several components (HE
power law, LE power law, multi-temp diffuse, broad iron line, reflection comp,
PL break). Comparing radio quiet vs radio loud AGNs, power law indices are
about the same. The Fe line energy is higher, and has a wider eq width than fo
r
radio loud. Also, the reflection component appears weaker. Rick uses PCA data
out to 30 keV. The model includes power law + wabs, iron line. Rick showed a
combined HEXTE+PCA spectrum (factor 1.67 norm factor). There is some evidence
of a rolloff at ~150 keV but statistics are not very good. Rick showed various
model fits, varying the reflection component and line width. The fits depend
most on the width of line. The best fit model is a weak reflection component.
Rick noted that the reflection component couples to an asymetric iron line.
0947 Mike Stark - Bursting Pulsar
Mike examined the question of the origin of the bursts and how the pulsar
behaves as a function of the source luminosity. He showed a long term light
curve extending back to the XTE launch. The detailed LC shows occasional large
bursts superimposed on 2 ms pulsations. The phase shift appears to not
correlate with the size of the burst. He examined the low count rate behavior.
He showed a period of noisy bursts superimposed on a quiet "background" level
for which no pulsations are observed. He showed a plot of relative pulse
amplitude vs time. The peak does not coincide with the intensity peak.
He showed pulse phase and pdot vs time plots exhibiting considerable structure.
Fred Lamb commented that the propeller mechanism requires no accretion but
involves heating outside of the magnetosphere. Fred has a centrifugal barrier
mechanism which makes different predictions.
1010 Al Levine, Ed Morgan - ASM detection of GRBs
ASM detected its first burst one month ago. They will able to report a
position in ~12 hrs. The burst profile shows an initial peak then more
structure at ~100 s. Al showed raw count rate profiles with source exposure
superimposed. Al showed the ASM error boxes vs IPN and BATSE locations. The
next burst observed was 28 Aug (relatively strong). Al noted that the x-ray
profile was much different (longer) than the gamma-ray profile. ASCA observed
a source within the ASM/BATSE error boxes. Al showed a fast BATSE burst (not
a classical burst, more likely a soft gamma-ray repeater). ASM apparently saw
this burst for 2-3 s. The error box does not coincide with any known ROSAT
source. Their initial estimate for the extent of the error box in the long
direction was apparently in error. Al feels that the error box could easily
be larger and coincide with the IPN error boxes. There were two bursts in the
same day from this position.
1035 Frank Marshall - RXTE Quick response Obs of GRB Afterglow
The goal is to enable multiwavelength followup for the brightest GRBs. He
hopes to improve positions from the PCA scanning data. XTE can respond more
quickly than Beppo/SAX but has no imaging. He expects 2-4 candidate bursts
per month (bright enough and in acceptable locations). Frank is confident
that the source PCA saw was the burst since it faded within 1 day. It should b
e
an advantage to use the smaller ASM error box which are easier to scan. Frank
shows a light curve extending to 10e5 sec. PCA viewed it at the few mcrab
level. The decay rate was t exp(-1.4). There may be some evidence for
variability, but this could be a background effect. It is possible in this
case to recheck the level of sky fluctuations. This burst not detected down
to 24th mag. This may be a problem for the theory of a (strong) burst.
1050 Fred Lamb - Modeling KHz QPOs
Fred showed a plot of Atoll vs "Z" sources. Z sources have stronger fields
dominating accretion flows. He claims that GR effects are important in the
interpretation of these objects. He notes there is no mechanism for producing
QPO at the Keplarian frequency. He showed a plot of B vs M/Mdot. He also
showed a schematic view of the GR modeled flow of an element of matter onto a
star. Continuous flow (~9 circuits) produces a broad luminous disk. An
episodic, clumpy flow would fall more directly onto the star. He notes the
interaction of the orbiting flow with the beaming hot spot. Fred showed a
video demonstrating the mechanics of the model. The model predicts 10 Hz
broadening of KHz QPO peak and a variety of other effects. He described the
slow drift to the "sonic point", then a transition to hypersonic flow. He
predicts that the Keplarian frequency will increase with luminosity then flatte
n
at L/LE ~ 0.04. He calculates a steep rise in amplitude with increasing photon
frequency. He also predicts that the RMS amplitude will decrease with
increasing stellar magnetic field. Sco x-1 presumably has high field, 4U
0614+091 is a weak field example. Sco exhibits ~1% amplitude, 4U 0614+091
shows ~15%. Fred showed curves of mass vs radius that limit the radius to ~15
km if a coherent ocsillation is shown. This is an exciting result for
constraining equations of state. Higher QPO (above 1220 Hz) would constrain
the radius to smaller values, inconsistant with some equations of state.
1145 Ed Morgan - PCA Deadtime Task Force
Ed addressed the "differential dead-time" issue. He showed PSD data vs
predicted Poison noise levels. The process affects the lowest energy channels.
Ed noted the effect in PSD where power below 2 Khz is affected by ion drift
in the detector. He showed an 8us oscillation in a Seyfert 1 AutoCorrelation
analysis. The deadtime is modeled to better than 1%, but needs work at
frequencies above a few KHz.
1202 Dan - PCA Background
Dan thinks the committee should make some kind of statement on the PCA plan for
modeling the background. Jean notes that the PCA team is slightly undermanned;
they hope to add a junior level postdoc. She thinks they need to renew their
dedication to solving the problem. Fred suggests that the PCA team establish a
written document, updated periodically, giving the status and prospects for the
background model. Jean notes that they have recently established such a
document and it is posted on the web. Keith notes that the background errors
can be compensated in the analysis [using GRPPHA?]; however, Frank notes that
this doesn't really solve the problem. For short observtions, the background
errors are actually overestimated. Fred thinks we need to reach out to users
who have weak source observtions and let them know the limitations of the data
and also get feedback on what their problem are. Rick Edelson suggests a set
of recipes describing how to attack various analysis problems. He specifically
suggests a talk at the HEAD meeting on this topic. Fred observes that we need
to change the perception in the community that the PCA data have intractable
background correction problems. This implies that one or more of the talks
needs to address this issue in addition to the scientific results. Dave Smith
doesn't want to overemphasize outreach or PR activities if they might compromis
e
real progress on the background problem. Dan doesn't think we are on the verge
of a breakthrough and that the outreach approach has the potential of
"leveraging" the efforts here on the problem. Fred suggests that the UG
recommend re-establishing the investigator team interactions and that the PCA
team renew their commitment to progressing on the background problem. Rick
Rothschild thinks the PCA team needs to establish a full-time person to be the
point of responsibility to work the background problem. Fred wants a written
report on the status and plans for solving the problem. Kim will be the point
of contact with the user subgroup. The PCA group will meet to discuss things
and decide how they will respond to the problem. Al Levine thinks the PCA team
might benefit from the experiences of other outside people who have worked on
background modeling for other missions.
1240 Dan/Fred - Move to discussion of the Senior Review
Fred suggests that Jean disseminate the results from the previous review.
He wants to establish ( a group?) to track the development of potentially
exciting results so that we can exploit these to the maximum extent in
preparing for the review. He suggests 3 or 4 people from the user group
periodically update Jean on developments in their particular areas. Padi
Boyd is tracking and documenting XTE publications. Fred suggests contacting
XTE users on 3 month intervals to check the publication list on the web and
help update that database. Fred wants to designate a few people to work with
Jean on presenting results at meetings during the period up to the review.
Rick suggests we consider nominating someone for an award (eg the Rossi prize).
Jean reports that Lin Cominsky isn't inspired to have a press conference on
any of the XTE topics. UG recommends encouraging her to reconsider, perhaps
by educating her as to the substance behind some of the work. The UG needs to
begin preparation of its presentation for the review. Rick notes that ROSAT
had a special session at the San Diego HEAD mtg to organize their preparations
for the senior review. It may be appropriate to do something similar at the
winter AAS. We should consider organizing a special meeting in the summer
(when there currently appears to be a dearth of meetings). Fred appoints
Rick to investigate the possibility of organizing a special workshop at the
summer AAS [or ?]. Padi notes that the APS is organizing its spring meeting
and special sessions this weekend (Josh Grindley).
1309 - The next meeting was scheduled for: 30-31 March, 1998
1425 - Reconvene executive session
Jean distributed copies of the Guenter's announcement from the last senior
review and the current budget allocations (POP, pre and post senior review
budgets). Paula noted that, in the last review, XTE ranked third. It is
important to be ranked first or second, since those missions are likely to
get all (or more) of the funding they request. The group discussed the figures
as they currently exist.
This group needs to decide whether we will request funding beyond the presently
planned figures. Frank distributed his general plan for the 3rd year. The
third year allocation is ~70% of current year with plans to go to 50% in the
4th year. By the 4th year, MOPS would be reduced to one shift/day. Frank is
optimistic that automated monitoring will be adequately functional by the 3rd
year. Jean and Frank feel that the XTE operation is leaner and more efficient
than any comparable previous mission at this phase. There has been a suggestio
n
from Jim Kurfess to combine operations with GRO and perhaps TRIM in the post-
2000 timeframe. This was considered but did not get very far. Frank notes
there is probably some savings to be gained by combining with TRIM (for which
the spacecraft is very similar to XTE). The problem is that by then, the MOPS
budget is already very small; thus, there isn't much to be saved.
There would be a more extensive beeper system with instrument team members on
call to respond to problems to a much larger extent than their present
responsibility. Rick thinks that we will have to accept the reality that
reaction times to a problem will be longer than at present. Fred asks whether
the planning is in place to leave the data and software, etc. in orderly
condition when mission funding ends. Anne Cowley noted that electronic/conf
call proposal reviews are quite adequate in her experience and that this is one
avenue for reducing the costs. Al Levine recommended streamlining the whole
proposal process. We should also consider 2 year proposal cycles. Dan notes
that the instrument team funding needs to be settled prior to the next UG
meeting. Rick wonders whether full cost accounting is likely to have an effect
on these costs. Paula suggests that the project should work out their drop-dea
d
funding levels as a reference point for us and for the senior reviewers.
Minutes submitted by M. Pelling, 6 Nov, 1997
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