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ROSAT Status Report #153: ROSAT NEWS No. 54
Date: Tue, 3 Jun 1997 14:15:46 +0200
Subject: ROSAT NEWS No. 54
=========================================================================
= =
= ROSAT NEWS No. 54 --- 3-Jun-1997 =
= =
=-----------------------------------------------------------------------=
= ROSAT Scientific Data Center at the =
= Max-Planck-Institut fuer Extraterrestrische Physik (MPE) =
= Postfach 1603, D-85740 Garching, Germany =
=-----------------------------------------------------------------------=
= e-mail address: rosat_svc@mpe-garching.mpg.de =
= ROSAT Service Area (including ROSAT Data Archive): =
= www address: http://rosat_svc.mpe-garching.mpg.de/ =
= ftp rosat_svc.mpe-garching.mpg.de user: anonymous =
= interactive account (including ROSAT Result Archive): =
= telnet xray.mpe-garching.mpg.de user: xray no password =
=-----------------------------------------------------------------------=
= XUV Center: GXUVDC@AIT.PHYSIK.UNI-TUEBINGEN.DE =
= WFC Archive access via telnet/ftp ait.physik.uni-tuebingen.de =
= user: xuv (password: xuv_archive) =
= www address: http://astro.uni-tuebingen.de/rosat.html =
=========================================================================
Contents: ROSAT 7-TH BIRTHDAY
ROSAT BATTERY RECONDITIONED
ROSAT TIMELINE
AO-8 PROPOSALS
UNPLANNED HRI GAIN REDUCTION
HAMBURG/RASS CATALOGUE OF OPTICAL IDENTIFICATIONS (HRC)
ROSAT 7-TH BIRTHDAY
===================
On June 1, 1997 the ROSAT observatory completed the 7-th year of an
extrememly successful mission. During the life of ROSAT the data centers
received proposals from about 780 different PI's from 26 countries, the
overbooking being still a factor 4 to 5. In addition to the ROSAT All-Sky
Survey more than 6700 pointings with a mean duration of 12.9 ksec on
specific targets have been performed. In total more than 150.000 new
X-ray sources have been detected in the data.
Although rumours about diminishing support of this long-lived mission are
circulating from time to time, the German space agency DARA has declared
its definite intent to support the ROSAT activities of the German Space
Operation Center (GSOC) at least up to the end of 1998.
We therefore hope that the rejuvenating cure (see next item) ROSAT
has just undergone will enable us to continue the successful programme
also during the eighth year.
ROSAT BATTERY RECONDITIONED
===========================
>From May 30 to June 3, 1997, a reconditioning of the ROSAT battery was
performed: after disconnecting it from the spacecraft main and charge
bus, the battery was completely discharged over a period of 72 hours,
and then recharged within 5 hours. At the beginning of this operation
ROSAT was put into safemode (May 30, 1997, 19:45 UT to June 1, 1997,
9:15 UT); after that, a reduced observing programme (sun angle of
targets within 80 and 100 degrees) was executed until June 3, 1997,
20:00 UT.
According to the specifications of the manufacturer, the nominal
battery lifetime is about 35000 charge/discharge cycles, if no
reconditioning is performed. Until now, the ROSAT battery has
undergone more than 37000 such cycles. During the past few months the
end of the nominal battery lifetime was indicated by individual cell
voltages reaching values only a few hundredths of a volt above the
threshold where all non-essential loads (including the focal
instruments !) will be disconnected from the spacecraft power supply.
A prerequisite for the battery reconditioning is a sufficiently long
period of full sun orbits, since there is no backup battery available
onboard. Such periods occur about twice per year, the period starting
on May 30 being the best opportunity in 1997.
It is expected that the reconditioning will significantly improve the
quality of the battery for at least one year.
ROSAT TIMELINE
==============
A new timeline and a timeline summary covering the period June 16 to
December 14, 1997 is available via the ROSAT Service Area (files
ao7_hri4.timeline and ao7_hri4.summary in directory timeline). The
www address is http://ftp.rosat.mpe-garching.mpg.de/rosat_svc/timeline/.
All PI's are asked to check whether the coordinates of their accepted
targets have been correctly implemented.
In the same directory also the master_obs_h.list has been updated,
containing now all HRI observations performed until March 11, 1997.
AO-8 PROPOSALS
==============
The deadline for the next round of ROSAT proposals is June 16, 1997.
Info on past and planned observations is best inquired via the 'Archive
Browser' at http://www.rosat.mpe-garching.mpg.de/~jer/rda/archive.html
or via the master_obs_h.list or master_obs_p.list (see previous item).
Proposals have to be submitted using the RPS (remote proposal system).
Details see in http://ftp.rosat.mpe-garching.mpg.de/rosat_svc/general/rps.
UNPLANNED HRI GAIN REDUCTION
============================
While turning the HRI back into the focus of the ROSAT XRT on March 3,
1997 (after the PSPC intermezzo), the HRI instrument switched erraneously
to the high voltage setting 12 used at the beginning of the mission. The
error was only recognized two months later and the HV was reset to step 13
(which has been used since 1994 Jun) on 1997 May 6 at 12:40 UT.
D. Harris & J. Silverman from the SAO RSDC looked at some data to
estimate possible consequences of the low gain situation:
Fortunately, our monthly calibration source, N132D, was observed
during this period. From examination of 2 (of the 3) observations of
N132D, we conclude that the effects of the lower gain are consistent
with expectations.
- The pulse height channel distribution has shifted to lower
values; most of the counts appear in channels 2 and 3.
- The mean channel of the PHA distribution has continued to
decrease with time (from the beginning of the mission).
- The quantum efficiency (using all PHA channels) has not
changed significantly.
Plots are available via:
http://hea-www.harvard.edu/rosat/rsdc_www/hri_status.html
What effects will there be on the data observed during this period?
We suspect that most observations will not be affected by the lower gain.
However,
a) Constructing hardness ratio maps will be more difficult because
most of the counts are 'squashed' down into fewer channels.
b) Those users who are in the habit of discarding events in the
higher PHA (to improve s/n by rejecting particle induced counts)
should expect to find that more channels can be rejected (e.g.
for the HV=12 recent data of N132D, we could reject channels 6-15
rather than 9-15).
c) For those sequences which contain some obis at HV=12 and others at
HV=13, any sort of spectral manipulation or measurements should treat
each segment of the data separately.
Please direct any questions to: rsdc@cfa.harvard.edu
HAMBURG/RASS CATALOGUE OF OPTICAL IDENTIFICATIONS (HRC)
=======================================================
The Hamburg/RASS Catalogue of Optical Identifications (HRC) comprising
3847 RASS X-ray positions on the extragalactic northern sky is now
available. The catalogue was derived by correlating the ROSAT All-Sky
Survey Bright Source Catalogue (1RXS) with a database of optical
identifications of ROSAT All-Sky Survey sources, maintained at the
Hamburger Sternwarte. This database provides information on optical
counterparts obtained from objective prism and direct Schmidt plates
of the Hamburg Quasar Survey. For each X-ray position the optical
counterparts within the error circle are listed and a finding chart
derived from the digitized direct plates is provided. If possible, the
most likely optical counterpart is marked in the catalogue and on the
finding chart.
The HRC is availbale electronically at
http://www.hs.uni-hamburg.de/hrc.html
==========================end of NEWS ===================================