Prepared by: Alex Brown, Chair
Members Absent: Chris Mauche and Craig Sarazin Others: Keith Arnaud, Mark Bautz, Nancy Brickhouse, Ken Ebisawa, Keith Gendreau, Pat Henry, Duane Liedahl, Koji Mukai, Rob Petre, George Ricker, Rita Sambruna, Nick White, Tahir Yaqoob
Welcome - Alex Brown
Those attending were welcomed by the chair and minutes from the
previous meeting were approveded.
This meeting is likely to be the last meeting of the ASCA User's
Group and attempts to close the remaining issues relating to
GO usage of ASCA.
Mission Status - Nick White
The ASCA satellite is in its sixth year of operation and reentry of the spacecraft is likely to occur at some (uncertain) time during 2000, with a best guess relatively late next year. In May 1999 Chip 2 of SIS 1 failed, although this has little observational impact as it was not the prime chip. The SIS 6 keV spectral resolution is now three times worse than at launch but still better than the GIS. The SIS low energy (< 1 keV) efficiency still continues to decline.
During the 1998 Senior Review ASCA was ranked 6th out of 8 missions. This ranking was strongly influenced by concerns about the evolving time-dependent instrumental calibration difficulties and the resolution degradation of the SIS detectors. ASCA received funds at the requested minimum level for an extended mission phase. However this level of funding compromises efforts to tackle the calibration problems and little progress is likely in this area once Astro-E is launched.
In 2000, when Astro-E is operating, ASCA will need to move to long 1-4 week observations, because ease of operations will be the prime operational constraint. Cross calibration observations with Chandra (AXAF) and Astro-E are still planned. An informal call for proposal for long observations beyond AO-7 will be released soon, with a due date of 12 October 1999. Instrumental experimentation, such as annealing, may be attempted near the end of the mission.
The ASCA archive now comprises 450GB in the HEASARC, roughly one third of the total. Archives have been exchanged with the University of Leicester, England and the BeppoSax project. Over 200 ASCA-related papers have appeared over the past year, so ASCA scientific analysis is clearly very active.
AO7 Proposal Review - Rob Petre
Rob summarized the AO7 review process. The observing time allocated was
increased by an additional three months in anticipation of a potential
early reentry. 600 ksec was held back initially to encourage acceptance
of long observations. The largest accepted exposure was 480 ksec.
Full electronic submission was used and, while this was well
received by the proposers, the proposal reviewers had significant
reservations regarding the effort of printing the proposals and
the resulting lack of proposal security. Of 102 submitted proposals,
59 were accepted.
The US/Japan merging was again attended by review panel representatives
Chris Mauche and Wilt Sanders. Eleven target overlaps occurred - 2 US and
2 Japanese proposals were consequently dropped.
There were five ESA - US clashes that
resulted in the ESA target being dropped.
The AUG once again expressed their concerns regarding the ADP
review process, through which ASCA GO funding is now channeled,
and assuring that adeqaute X-ray experience is reflected in
the panel composition.
Calibration - Tahir Yaqoob
Current information on the status of ASCA calibration is
available the ASCA CAL webpage.
Divergence in instrumental sensitivity below 1 keV between the
different SISs and the GISs continues. The problem has grown
progressively worse since late 1994. The cause of the effect
is not understood but is possibly due to changes in the dark current
and charge transfer efficiency models. The standard background data
cannot be successfully used for later pointed data.
Improvments in the GIS calibration relate to the X-ray telescope
optical constants and the energy-pulse height conversion. Ongoing
calibration work is being conducted by the GIS team and, while these
result in relatively small changes to the arf files, the energy
conversion is better.
Jules Halpern illustrated the current level of calibration problems
using data obtained in January 1999.
SIS Calibration - Koji Mukai
The CTI effect continues to degrade the spectral resolution and
increase the number of flickering pixels. The RDD problem also degrades
resolution and detector efficiency. A new version of the calibration
software and files
will be released at the end of the summer, with a test version available
Recommendation passed by the AUG: The AUG strongly encourages completion
and documentation, ideally in a refereed form, of an adeqaute
calibration of the ASCA instruments
before the launch of Astro-E. Characterization of the temporal behavior of
the calibration is important.
Recommendation passed by the AUG: The AUG endorses the plan for post-AO7
operations and the use of long observations. Near the end of the mission
instrumental investigations of annealing etc. should be attempted, because
of their importance in understanding the operation and degradation of CCD
detectors in space.
Recommendation passed by the AUG: The AUG endorses the cross-calibration
efforts involving ASCA and other X-ray satellites.