Compton Observatory Science Report #155 Friday, April 15, 1994 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 The Observatory, scientific instruments and all spacecraft subsystems continue to performing normally, except for one anomaly ionvolving the BATSE instruments which is described in detail below. Science Support Center News The interest in CGRO science from the astrophysics community is quite healthy - a total of 234 CGRO Cycle 4 were received! The proposals have been logged in, and are currently being sorted by the SSC staff. A peer-review meeting will take place in late June, followed promptly by time line development. Final results should be announced during July. As noted in the COMPTEL report, there are now plans to establish the SSC as an additional "COMPASS" site - this will allow guest investigators full access to low-level COMPTEL data. Instrument Reports EGRET EGRET operations were normal this biweekly period. The average percentage of possible data recovered remains about 80% or above. Interactions with guest investigators remains at a good level. At present EGRET is in the middle of the Mkn 421 observation. This source is of interest because it is the only AGN seen by EGRET that has also been seen at TeV energies. Several other quasars of interest to EGRET are also in the field of view. As noted two weeks ago, several papers related to EGRET results will be presented at the APS meeting next week including ones on galactic sources, the diffuse radiation, the search for microsecond bursts, and AGNs. Of particular interest will be a paper presented on the February 18, 1994 burst wherein two characteristics suspected from an earlier burst were confirmed. They place significant constraints on theories trying to explain these bursts; in fact several theories are simply not consistent with the observation. OSSE OSSE operations are normal. In viewing period 322 (5-19 Apr), the Z-axis target is QSO 1028+313 (Guest Investigator M. Maisack), and the X-axis target is the blazar PKS 0528+134 (Key project). In the portion of each orbit in which neither target is above the horizon, the lower detectors are testing a mapping strategy in the region of (l,b) = (175,-75). The Sun is not available for slewing on the OSSE scan plane. Data from the following viewing periods have been sent to the Compton GRO Science Support Center archive in the last two weeks. period targets 202 Her X-1, galactic plane near (l,b) = (355,0) 203.0 Cyg X-1, galactic center region, GX301-2 203.3 Cyg X-1, Cyg X-3, galactic center region, GX301-2 203.6 Cyg X-1, galactic center region, GX301-2 206 3C273, 3C279, galactic plane near (l,b) = (355,0) BATSE The monolithic time to charge convertor (MQT) for LAD 3 experienced a latch-up event on March 30th, and again on April 5th. Both events resulted in the loss of all analyzed count spectra from the detector. The first event lasted for 31 hours, and the second for 7 hours. In both cases normal operation was restored by cycling power to the module. Similar events have occurred before with this MQT. As of April 12, BATSE has detected 955 cosmic gamma-ray bursts out of a total of 2817 on-board triggers in 1085 days of operation. There have been 729 triggers due to solar flares with emission above 60 keV. COMPTEL The COMPTEL instrument is performing well and continues routine observations. Following a decision taken at a recent team meeting, the COMPTEL collaboration is pleased to announce its intention to release the COMPASS data-analysis software package to the CGRO Science Support Center, for use by Guest Investigators at the SSC. This analysis software will complement the COMPTEL data already being delivered to the CGRO archive at the SSC, and is intended to facilitate and foster increased use of COMPTEL flight data for scientific programs by investigators outside the COMPTEL team. The installation and verification of COMPASS at the CGRO SSC will necessarily require some period of time prior to public availability, but initial discussions regarding the details of the implementation are already underway between the COMPTEL team and members of the SSC technical staff.