Compton Observatory Science Report #169, Monday October 28, 1994 Chris Shrader, Compton Observatory Science Support Center Questions or comments can be sent to the CGRO SSC. Phone: 301/286-8434 e-mail: NSI_DECnet: GROSSC::SHRADER Internet: shrader@grossc.gsfc.nasa.gov Spacecraft Status The Observatory, scientific instruments and all spacecraft subsystems are currently functioning in a nearly flawless manner. We note that the responsibilities of the Compton GRO Project Operations Director were transferred from Robert Wilson to Keith Walyus on October 17. Robert Wilson, who has served in that role since launch, is retiring on November 3. Best wishes to Bob and many thanks for his years of outstanding service to the project! Instrument Reports EGRET EGRET operations were normal this biweekly period. Delivery of data to the CGRO-SSC remains on scheduled. Interactions with Guest Investigators remains at a good level. A paper giving very detailed results on the Vela Pulsar appeared in Astronomy and Astrophysics (Kanbach et al., A&A 289, 855). Energy spectra as a function of phase in the period are provided allowing a comparison to pulsar theories that was previously not possible. Several EGRET papers will be presented at the forthcoming HEAD meeting, including an invited talk on the diffuse radiation and a paper presenting the evolution of gamma-ray bright blazars based on the gamma-ray data alone. OSSE OSSE operations are normal. In viewing period 402.0 (18-25 Oct), the Z-axis target was the galactic plane near (l,b) = (310,0) (Guest Investigator J. Skibo), and the X-axis target was 3C279 (PI team). In viewing period 402.5 (25 Oct - 1 Nov), the Z-axis target is again the galactic plane (l,b) = (310,0) (Guest Investigator J. Skibo), and the X-axis target is LMC X-1 (PI team). Several more interesting OSSE results have recently been accepted for publication in ApJ Part 1 or 2 and will be distributed as preprints shortly. L.-S. The et al. report that OSSE upper limits on Ti-44 line emission from Cas A are somewhat lower than the flux reported by COMPTEL. Grabelsky et al. give spectra from the black hole candidate GX339-4 in outburst and quiescence, with a strong indication of a direct correspondence between the low X-ray state and gamma-ray outbursts. Smith et al. report very stringent upper limits on Compton-back-scattered annihilation radiation from the galactic center covering >180 days of observation. Data from viewing period 228 were delivered to the Compton GRO Science Support Center archive this week. The targets were SN1993J and the Vela Pulsar. COMPTEL The COMPTEL instrument is performing well and continues routine observations. The collaboration will be well represented at next week's HEAD meeting in Napa Valley, California. In addition to an invited talk by R. Diehl on gamma-ray line spectroscopy with GRO, there will be presentations on active Galactic nuclei, x-ray binaries, and gamma-ray bursts observed by COMPTEL. During the week following the HEAD conference there will be a general team meeting of the collaboration at MPE in Garching, Germany. BATSE Many of the BATSE team scientists will be presenting papers at the HEAD meeting next week at Napa. Most are currently working hard to finish preparations for their presentations. The x-ray transients GRO J1719-24 = GRS 1716-249 and GX 339-4 are still in outburst. The following sources were detected by the BATSE pulsed source monitor in the past two weeks: Cen X-3, 4U 1626-67, 2S 1417-624, GX 1+4, Vela X-1, and GX 301-2. The outburst of 2S 1417-624 has now lasted 63 days. As of October 27th, BATSE has detected 1150 cosmic gamma-ray bursts out of a total of 3155 on-board triggers in 1283 days of operation. There have been 740 triggers due to solar flares with emission above 60 keV. Since the BATSE burst trigger criteria were changed, there have been four triggers due to atmospheric gamma-ray flashes.