Compton Observatory Science Report #129 Thursday, July 22, 1993 Eric Chipman, Compton Observatory Science Support Center Questions or comments can be sent to the Compton SSC. Phone 301/286-7764, e-mail SPAN GROSSC::CHIPMAN, Internet chipman@grossc.gsfc.nasa.gov. Science operations are continuing. GRO B-side OATs manifold is now primed. The GRO propulsion system priming operation to provide propellant at tank pressure to the two B-side orbit adjust thrusters (OATs) was successfully completed on July 21, 1993. The experience gained in previous priming operations enabled this activity to be successfully completed well ahead of schedule. A B-side OATs engineering test burn is now being planned to help evaluate the orbit reboost options. Letters to the Phase 3 CGRO Proposers are being mailed out this week and next Monday. We expect to release a preliminary timeline for Phase 3 in next week's Science Report. BATSE ----- The following was submitted July 19 as an IAU Circular: A 0535+26 Wilson, R. B, Finger, M. H., Gibby, L., and Fishman, G. J., report for the BATSE/Compton GRO Observatory team: "Hard x-ray pulses in the energy range ~20 keV - 120 keV are currently being detected from A 0535+26. The present outburst was first detected on July 8. The pulsed flux increased slightly from then until July 13, and has remained approximately constant through July 17. The spectrum of the phase averaged pulsed flux on July 13 is adequately fit by a power law, having spectral index -2.3 +/- 0.5, with a flux of 5.7 +/- 1.1 x 10^-5 photons/cm^2/sec/keV at 50 keV. The pulse shape is very broad, with a sharp dip occupying ~0.2 in phase. The pulse period on July 17 was 103.377 +/-0.005s, corrected to the solar system barycenter. A reanalysis of earlier BATSE data shows that the source was also detected at weaker levels during Feb. 28 - Mar 26 (just prior to the optical activity reported from its companion HDE 245770 by Bartolini, et. al in IAU Circ. 5746), and June 20 - 27. Additional observations at optical and other wavelengths are encouraged." Since the 19th the A0535+26 pulsed and total flux have been gradually increasing. The Second Announcement and Call for Papers for the Huntsville Gamma Ray Burst Workshop has been mailed. Abstracts of papers are due on Aug.5. The Workshop will be held October 20-22. A copy of the announcement may be obtained from Ms. Dannah McCauley/USRA (workshop@batse.msfc.nasa.gov) or fax 205-895-9222. As of July 21st, BATSE has detected 715 cosmic gamma-ray bursts out of a total of 2347 on-board triggers in 820 days of operation. There have been 662 triggers due to solar flares with emission above 60 keV. COMPTEL ------- The COMPTEL instrument is performing well and continues routine observations. Many members of the team are presenting recent research results on behalf of the collaboration at the International Cosmic Ray Conference in Calgary, currently in progress. In the Tour de France, most observers have conceded the win to Indurain, since Fignon, his most formidable opponent, has retired from the race. EGRET ----- EGRET operations were normal this week. There were a few days in which there were more than the normal number of lock-ups, but in the last four days there has been only one; so, unless the highr rate reoccurs, it will be assumed to be a fluctuation, although an examination is being made to see if there is any correlation with a large number of parameters. Work continues to complete the full analysis of Phase 1 and the first analyses of the Phase 2 data. Interaction with Guest Investigators and other scientists with whom we are working continues at a good level. Several more results have been given to these scientists this week. A total of twenty-one EGRET papers have now been published in refereed journals and another ten have been accepted. OSSE ---- OSSE operations are normal. In this second week of viewing period 228, OSSE's targets and viewing priorities remain unchanged. The Z-axis target is the recent supernova SN 1993J, and the X-axis target is the Vela pulsar (PI team). During those portions of the orbit in which both targets are visible, we have assigned viewing priority to the supernova; thus the pulsar is receiving only a small amount of livetime. During the significant portion of the orbit during which neither target is visible, engineering data are being collected to improve our calibration of the neutron v. gamma ray pulse shape discrimination efficiency. Because the Sun is not available on the OSSE scan plane, the slewing response to BATSE solar flare triggers is disabled. There have been no slews to the Sun since the last report. OSSE data from the activation period (second third, 91/118-127) have been reprocessed and will be delivered to the Compton GRO Science Support Center Archive today. A number of targets were viewed with limited livetime during that interval, including the Crab Nebula, Geminga, NGC 7582, and the Sun.