MINUTES OF THE ASCA USER'S GROUP

8 June 1999

Building 26, Goddard Space Flight Center, Greenbelt, MD

Prepared by: Alex Brown, Chair

Members Present: Alex Brown, Ed Guinan, Jules Halpern, Mark Henricksen, Christine Jones, Greg Madejski, Paul Plucinsky, and Kim Weaver

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 soon.

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.