Compton Observatory Science Report #119 Thursday, May 13, 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. The Compton spacecraft continues normal operations. There was a maneuver on May 13 to the attitude of 221 (z-axis target= Crab pulsar, x-axis target = PSR 1951+32). The maneuver times were 1527 - 1559Z, and the maneuver covered an angle of 104.5 degrees. The HGA Boom angle with respect to the equator is 14.9 degrees. A recent IAU circular (IAU Circ 5787, May 11) reports that the optical spectrum of SN 1993J is transforming itself from a Type II supernova to a Type I supernova. This has implications for the potential observability of this object as a gamma-ray source, and we are looking at some predictions of when a Type I should possibly show gamma-rays. No decisions have been reached yet on the CGRO timeline. BATSE ----- During viewing period 221 BATSE folded-on-board pulsar data will be collected for the Crab pulsar, PSR 0540-693, PSR 0950+08, PSR 1823-13, PSR 1822-09, Her X-1, and PSR 1508+55. Due to the very low level of magnetospheric activity, we have suspended the usual disabling of the burst trigger in geographic regions that have a high probability of a false triggers. If there is an increase in solar activity, the trigger disable may have to be resumed. As of May 11, BATSE has detected 642 cosmic gamma-ray bursts out of a total of 2232 on-board triggers in 748 days of operation. There have been 646 triggers due to solar flares with emission above 60 keV. COMPTEL ------- Following the test activities last week related to the propulsion subsystem aboard the GRO spacecraft, the COMPTEL instrument was reactivated without incident on Saturday, 8 May, and has resumed normal scientific observations. Communication with the experiment was sporadic for several days, however, due to numerous interruptions in the transfer of real-time data over the X.25 data-transfer line linking the Goddard Space Flight Center and the COMPTEL ground-support equipment at the University of New Hampshire. Normal communications were restored late Tuesday, following the replacement of a faulty connector module at NASCOM. The Sun will be within the field of view of COMPTEL following Thursday's maneuver to begin Observing Period 221. The solar observing mode of COMPTEL will be enabled during these observations. EGRET ----- EGRET operations were normal this week except for the adjustments for the reboost test. In all cases, the return to normal operations after the adjustments was nominal. Data reduction and analysis proceeded normally this week with there still being a heavy concentration on finishing Phase 1 work. Interaction with guest investigators and collaborators remains at a healthy level. OSSE ---- OSSE operations are normal. Following the thruster calibration burn last Friday, OSSE returned to science mode. For viewing period 220, the Z-axis target was SMC X-1 (PI team) and the X-axis target was the Seyfert galaxy 3C120 (GI: G. Reichert). During the portion of the orbit in which neither target was available, the detectors were configured as a cosmic-ray telescope to verify the calibration of the >10 MeV energy channels. The Sun was not available on the scan plane, so the slewing response to BATSE flare triggers was disabled. For viewing period 221, the Z-axis target will be the Crab Nebula and pulsar (PI team) and the X-axis targets will be 2CG135+01 (PI team) and the radio pulsar PSR 1951+32 (PI team). In addition, one day will be spent on Cyg X-1 to monitor its state. The Sun will not be available on the scan plane, and the slewing response will be disabled.