Compton Gamma Ray Observatory Status Report #203 Wednesday April 9, 1997 Questions or comments can be sent to Chris Shrader at the CGRO-SSC. Phone: 301/286-8434 e-mail: shrader@grossc.gsfc.nasa.gov Guest Investigator News The Compton Symposium is less than three weeks away! The response to the call for papers (over 300 abstracts) and the number of registrants (over 260) has exceeded our expectations and a memorable event is anticipated. A reminder, the Cycle-7 NRA was issued last month, and copies are available via the World Wide Web (http://www.hq.nasa.gov/office/oss or http://cossc.gsfc.nasa.gov). For paper copies, contact Sandy Barnes: barnes@grossc.gsfc.nasa.gov. Proposals are due June 12. Following several engineering tests during March, a series of orbit-adjust maneuvers were successfully carried during the first week of April. As of April 6, 1997, the 6th anniversary of its release from the Space Shuttle, the CGRO spacecraft is now in an orbit with mean apogee height of 517 km. An additional series of maneuvers during the later part of May and early June will circularize the orbit. The skill and dedication of the flight operations team in planning and executing these critical stages of the reboost operation is to be commended. The observatory can now be operated well into the next century without danger of early reentry. Once again, a reminder - it is extremely important that we at NASA be kept informed of any new scientific results involving CGRO. Please, if you have not already done so add us to your preprint mailing list (be it conventional or electronic) for any CGRO related work. Thanks in advance; CGRO Science Support Center, Code 660.1 NASA/GSFC Geenbelt, MD 20771, atn: C. Shrader; shrader@grossc.gsfc.nasa.gov. Instrument Team Reports EGRET EGRET concluded a extended observation of PKS 0528=134 just prior to the orbit boost activity. Except for possible Targets of Opportunity, the spark chamber will remain disabled until early August. The energy calorimeter remains active, and the spark chamber will be automatically for bursts that BATSE deterrmines to be within the EGRET field of view. Several tests of the instrument are planned during the hiatus. The EGRET team is preparing papers, posters, and talks for the upcoming Symposium. Software to analyze TASC spectra as well as the primary TASC data have recently been delivered to the GROSSC. GI and archival data deliveries are current or ahead of schedule. COMPTEL During the recent reboost maneuvers of the CGRO spacecraft, scientific observations with COMPTEL were suspended, and the instrument placed in a precautionary low-power state. With the successful completion of the CGRO orbital reboost, COMPTEL has once again resumed its normal scientific mode of operation. In another striking demonstration of Murphy's Law in action, the gamma-ray burst of 5 April 1997 occurred within the field of view of COMPTEL, optimally placed very near the instrument z-axis. Unfortunately, this GRB occurred while COMPTEL was in its low-power state during orbital reboost, and no scientific data could be collected for this event. A major delivery of both low- and high-level COMPTEL data products to the CGRO public archive at the COSSC has recently been completed. This delivery covers the balance of Cycle 4 (VPs 422 to 429.5), as well as extensive updates to previously delivered datasets with more recent datasets of improved quality. Serious preparations are now underway for team-related presentations at the upcoming 4th Compton Symposium in Williamsburg. Among the topics to be presented will be a review talk on the diffuse Galactic continuum emission, the latest results on the distribution of 26Al in the Milky Way, spectral properties of the MeV emission from the inner Galaxy, latest COMPTEL results on the Crab and Vela pulsars, as well as a number of additional reports on individual sources. OSSE OSSE operations are currently normal. The instrument is working as designed, with all subsystems in complete and full operation. During the first two delta V engineering/test burns of the CGRO OATs engines OSSE was left in low voltage mode until the maneuvers back to the viewing period 617.1 science targets. Following the first full delta V burn on day 97/091 OSSE conducted shield threshold and gain tests while chopping on the Crab Pulsar. Following these engineering tests OSSE began chopping on the Sun due to increased activity observed by GOES. During this time the slewing response to BATSE burst triggers was diabled. The return to science operations on day 97/097 has re-enabled the slewing response to BATSE burst triggers. Bursts, flares, and transients through April 4, 1997 have been processed. During this period no slews occured in response to BATSE triggers. results are available on the burst web site (http://www.astro.nwu.edu/astro/osse/bursts/). Recent observations are listed in the following table. 617.2 24 Mar (reboost: Butterfly test) 617.4 26 Mar (reboost: Engineering burn) 617.6 1 Apr (reboost: Burn #1 - Crab Pulsar) 2-6 Apr (Reboost: Sun) 617.1 - 18 Mar-10 Apr 3C 120 (W.N. Johnson) 617.3 GRO J2157+18 (public) 617.5 QSO 0834-201 (public) 617.7 Low-level OSSE data products through viewing period 508 are awaiting delivery to the Compton GRO Science Support Center archive. High-level data products through viewing period 220 have been delivered. In addition, by special request all subsequent public Cyg X-1 data sets, both low and high level, have been delivered. Refer to the CGRO-SSC page on the WWW (http://cossc.gsfc.nasa.gov), or contact Tom Bridgman (bridgman@grossc.gsfc.nasa.gov) for more information. BATSE The following appeared in IAU Circular 6585: GS 1843+00 R. B. Wilson and B. A. Harmon, Marshall Space Flight Center, NASA; D. M. Scott, M. H. Finger, and C. R. Robinson, Universities Space Research Association; D. Chakrabarty, Massachusetts Institute of Technology; and T. A. Prince, California Institute of Technology, report for the Compton Observatory BATSE Team: "Pulsations from the transient x-ray binary pulsar GS 1843+00 have been detected since Mar. 3 in the energy range 20-50 keV. Using observations through Mar. 9, the mean barycentric pulse frequency at epoch Mar. 6.0 UT was (3.382592 +/- 0.000035) x 10E-2 Hz. The observed spinup rate during this observation is (4.18 +/- 0.12) x 10E-11 Hz sE-1. The mean RMS pulsed flux integrated over 20-50 keV was (3.75 +/- 0.24) x 10E-10 erg cmE-2 sE-1 on Mar. 8-9. Earth-occultation measurements indicate a steady increase in total intensity from early March to Mar. 8-9, with a total flux of 5.1 +/- 0.5 x 10E-9 erg cmE-2 sE-1, giving a pulse fraction of about 7 percent. The thermal bremsstrahlung model (without Gaunt factor) yields a temperature of 23 keV. Pulsed and steady emission are also observed on Mar. 10. Updates to source intensity and pulse frequency are posted twice-weekly for this and all other bright sources detected by BATSE at the web site http://www.batse.msfc.nasa.gov. Observations are encouraged at all wavelengths, as no optical counterpart is currently known for this source." During the last month the following pulsed sources have been detected by the BATSE pulsed source monitor: Her X-1, Cen X-3, 4U 1626-67, GS 1843+00, OAO 1657-415,GX 1+4, Vela X-1,and GX 301-2. The burst trigger is currently using rates from channels 2+3 (50 - 300 keV), with thresholds of 5.5 sigma for all timescales. As of April 6 BATSE has detected 1750 gamma-ray bursts out of a total of 6055 on-board triggers in 2175 days of operation. There have been 782 triggers due to solar flares, 39 due to SGR events, 64 due to terrestrial gamma-ray flashes, and 1800 due to the bursting pulsar GRO J1744-28.