Compton Observatory Science Report #145 Friday, December 3, 1993 Chris Shrader, Compton Observatory Science Support Center Questions or comments can be sent to the Compton SSC. Phone: 301/286-8434 e-mail: NSI_DECnet: GROSSC::SHRADER Internet: shrader@grossc.gsfc.nasa.gov Spacecraft Status Phase II of the CGRO reboost procedure was successfully completed. Science operations resumed on 11/23/93, when the Z-axis of GRO was maneuvered to target 308.6 VIRGO 283+75. As of November 25, 1993 the Compton GRO orbit had an apogee of 453.2KM and a perigee of 408.6 km. The observatory has subsequently been maneuvered to target 310, Geminga on 12/01/93. The final three Phase II reboost burns are scheduled for December 15, 16, and 17. These burns will raise perigee with a resulting circular orbit of approximately 450 km. Science Support Center News Several problems with certain data sets archived at the SSC have been discovered: We have recently determined that the catalog and FITS headers for BATSE triggers greater than #525 may incorrectly indicate that the trigger is a burst rather than a solar flare. You may wish to check any bursts which you have previously analyzed against the BATSE Burst catalog on GRONEWS. A slight error (a 3.8% overestimate) in the EGRET exposure calculation for period 23.0 which will change the exposure and intensity maps has been discovered. Both of these problems are easily correctable and are being given immediate attention. Further details will be available on GRONEWS. It is now anticipated that the release of the Cycle 4 NRA will be delayed by two to three weeks. It is most likely that the NRA will be distributed in early January 1994, and that proposals will be due in late March or early April of 1994. In any case, the start of Phase 4 will occur as scheduled on 4 October 1994. Instrument Reports OSSE OSSE operations are normal. GRO reboost activities occurred in viewing period 308.3 (19-Nov-93 to 23-Nov-93). OSSE was placed in a low-power mode during the portion of each day that reboost operations were in progress. The instrument was then returned to a normal operating mode for the remainder of each day. During these times, engineering tests were performed and some science data was collected from the target Sco X-1. In viewing period 308.6 (23-Nov-93 to 01-Dec-93), the Z-axis target was the Virgo sky survey region (Key project) centered at (l,b) = (283,+75), and the X-axis target was the galactic plane near (337,0) (Key project). When neither target was available, i.e. when both were occulted by the Earth, OSSE observed the targets Mrk 421 and NGC 7213. In viewing period 310 (01-Dec-93 to 13-Dec-93), the Z-axis target is Geminga (PI team) and the X-axis target is NGC 4151 (GI: G. Reichert). The OSSE observation of NGC 4151 is part of a multi-wavelength AGN Watch campaign to simultaneously observe NGC 4151 from infrared to gamma-rays. During the period 3-Nov-93 through 29-Nov-93, OSSE responded to BATSE solar flare triggers with slews to the Sun on the following occasions (TJD=Truncated Julian Day): TJD 9297.8556 (Nov. 6), TJD 9307.2045 (Nov. 16) EGRET EGRET operations were normal this week. The Geminga observation started on 12/01/93. The deep survey will be continued at the end of the observation. Work continues on several papers including the several sections of the sky. Interaction with guest investigators continues at a good level. COMPTEL The COMPTEL instrument is performing well and continues routine observations. During the most recent series of reboost maneuvers of the GRO spacecraft, 18-23 November, COMPTEL was placed in a low-power mode as a safety precaution, and no scientific observations were carried out. The telescope was reactivated on 23 November without incident. The collaboration wishes success to the Hubble servicing team. BATSE Two occultations of the Crab Nebula by the Moon were observed by BATSE on November 30th. A systematic search for other occultations is being mounted. One additional occultation has been found so far and several more are expected. An attempt will be made to produce an image of the Crab Nebula with the Moon occultation step data. A problem was discovered in the durations table supplied to the GROSSC. Errors were found in six entries. The cause of the problem has been corrected, and a corrected table is now available on GRONEWS. During viewing period 310 BATSE folded-on-board pulsar data is being collected for the Crab pulsar, PSR 0525+21, PSR 1259-63, and PSR 1509-58. The pulsar hardware is also begin used to collect 31 ms single sweep data for pulsar searches on detectors 3 and 7 combined. As of November 27th, BATSE has detected 825 cosmic gamma-ray bursts out of a total of 2556 on-board triggers in 949 days of operation. There have been 688 triggers due to solar flares with emission above 60 keV.