Compton Observatory Science Report #170, Monday November 14, 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 spacecraft and all subsystems continue to function normally. A maneuver was uplinked on November 9, 1994 to point the Z-axis towards a target of opportunity, OJ 287, a BL Lac object which is undergoing significant photometric activity. These observations are being made under a Guest Investigator Program, and are part of a multiwavelength campaign. As noted in the EGRET instrument report below, the EGRET has been operated in a mode which reduces the field of view, and thus the number of spark triggers. It is anticipated that this operating mode will be used extensively in Cycle 5 and beyond to prolong the lifetime of the spark-chamber gas. A new verision of the Cycle-4 timeline, which reflects the changes resulting from the OJ 287 ToO has been sent to all Guest Investigators, and is also available on GRONEWS (grossc.gsfc.nasa.gov, username = gronews) or Xmosiac (http://enemy.gsfc.nasa.gov/cossc/cossc.html). Instrument Reports EGRET EGRET operations were normal this biweekly period. Delivery of data to the GRO SSC remains on schedule. Interaction with guest investigators continues at a good level. For period 403, EGRET was in the narrow telescopes only mode. When the target of opportunity mode began on Wednesday November 9, 1994, at the request of the Project Scientist and with our concurrence, it was left in the narrow telescopes only mode. It will be placed in the normal mode for viewing period 404. Several papers will be submitted to journals soon summarizing EGRET results for the entire sky. There will also be several talks presented at the Munich Relativistic Astrophysics meeting. OSSE OSSE operations are normal. A recent modification to an address in flight software resulted in our missing both of last week's slewable burst triggers from BATSE. The address has been updated, and we plan to get everything right for the next trigger. In viewing period 403.0 (1-9 Nov), the Z-axis target was Her X-1, and the X-axis targets were IC4329A and NGC 4945 (Guest Investigator R. Mushotzky). In Target of Opportunity viewing period 403.5 (9-15 Nov), the Z-axis target is the blazar OJ 287, and the X-axis targets are PG 1416-249, GRS 1716-249, and GX1+4. BATSE reports that both of the latter objects are currently in high states. Data from viewing periods 229, 229.3, 229.5, 230, 230.5, and 231 were delivered to the Compton GRO Science Support Center archive this week. The targets during these viewing periods are listed below. vp targets 229 galactic plane near (l,b)=(5,0), and Coma Cluster 229.3 PSR 1509-58 229.5 galactic plane near (l,b)=(5,0), and Coma Cluster 230 GRO J1008-57, Sun, and QSO 0716+714. 230.5 GRO J1008-57, Sun, and QSO 0716+714 231 NGC 6814 and NGC 4507 COMPTEL The COMPTEL instrument is performing well and continues routine observations. The COMPTEL Burst Rapid Response Team achieved a new breakthrough recently in the rapid processing of burst data. In the first test of a new automated data-processing system for bursts, an image of the COMPTEL field of view was obtained 8 minutes after the receipt of data from the BACODINE system; the transfer of BACODINE data occurred within minutes of a BATSE burst trigger on Sunday, 23 October. While no emission from this particular burst was detected in the COMPTEL energy range, this exercise demonstrates the practical feasibility of reducing the COMPTEL processing time to approximately 10 to 15 minutes for burst events occurring within the field of view of the instrument. The team will continue to further refine the data processing procedures for bursts. Ground-based observers interested in receiving COMPTEL burst alerts within approximately 10-15 minutes of burst occurrence should contact Dr. Bernie McNamara (NMSU) at bmcnamar@nmsu.edu. A general team meeting of the collaboration is being held this week at the Max-Planck-Institute in Garching, Germany. BATSE A new outburst of the x-ray transient GRO J1655-40 began on November 1st. By November 11th and 12th the 20-100 kev flux had increased to nearly 1 Crab. The x-ray transients GX 339-4 and GRO J1719-24 = GRS 1716-249 continue to be in outburst. The following sources were detected by the BATSE pulsed source monitor in the past two weeks: Her X-1, 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 81 days. The barycentric pulse frequency is again stop increasing, possibly indicating a second periastron passage. The x-ray binary GX 1+4, which has been spinning down since 1987, has been spinning up for the last week. As of November 12th, BATSE has detected 1158 cosmic gamma-ray bursts out of a total of 3177 on-board triggers in 1299 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 on September 19th, there have been 7 triggers due to atmospheric gamma-ray flashes.