Compton Observatory Science Report #135 Thursday, September 16, 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. NOTE: In an information note recently sent to planned attendees at the upcoming Second Compton Symposium, an incorrect date is given for the symposium banquet. If you are planning to attend this symposium please note that the banquet is scheduled for September 21 (Tuesday), NOT the 20th as stated in the letter. Science operations are continuing. The Target of Opportunity observation of GX 1+4 is proceeding. The reboost is now firmly planned for the B-side-only option (i.e. B-side OATS, B-side ACTS). It will now last from Oct. 4 - 17 and then from about Nov. 22 - Dec. 3. Also, it will be necessary, at least for the first set, to maneuver to the burn attitude 2-4 days early to stabilize the spacecraft thermally. Therefore the real start from the science point of view is about Oct. 1. This is a big hit on science, but it is considered essential to have a safe reboost. ARCHIVES -------- Archive contents- BATSE - Bursts to trigger 884, four months of daily HER and SHER data. Additional burst data up to trigger 1466 and corresponding HER and SHER data has been received at the SSC and is being installed in the archive. COMPTEL - Periods 1-13 are available Egret - Periods 0.2-30 are available (Maps and photon lists) OSSE - Periods 0.2-11 are available (SDB data). Pulsar data also available off-line. Additional data for Periods 12-13 has been received and is being installed. BATSE ----- The BATSE instrument is operating normally. Many BATSE scientists are currently preparing papers for the Compton Symposium. A delivery of BATSE burst and solar flare IBDB's was made this week to the Science Support Center. This included datasets for 126 gamma ray bursts and 236 solar flares. IBDB's have now been delivered for all the gamma-ray bursts in the first BATSE gamma-ray burst catalog. As of September 15th, BATSE has detected 769 cosmic gamma-ray bursts out of a total of 2426 on-board triggers in 876 days of operation. There have been 663 triggers due to solar flares with emission above 60 keV. COMPTEL ------- The COMPTEL instrument is performing well; target-of-opportunity observations of GX 1+4 are continuing. Research reports by the collaboration intended for presentation at next week's Compton Symposium are in final preparation at the various COMPTEL sites. EGRET ----- EGRET operations were normal this week. Because of the Target of Opportunity, the planned EGRET program is not occurring. Interaction with Phase 2 guest investigators and other scientists remains at a healthy level. Dr. Reshmi Mukherjee joined us this month from Columbia University. We are looking forward to the Compton Symposium next week. OSSE ---- OSSE operations are normal. For the current target of opportunity viewing period, the Z-axis target is the X-ray binary GX1+4 (GI: R. Staubert) in a high-intensity state, and the X-axis target is the Virgo-region sky survey (Key project), centered at galactic coordinates (298,+82). This attitude was chosen because it simultaneously minimizes potential source confusion from the galactic center for GX1+4 and avoids stressing any of the viewing constraints. When neither target is above the Earth's limb, engineering data are being collected to improve the energy calibration of the "high" spectral range, nominally >10 MeV. To provide a rapid assessment of the state of GX1+4, we are performing a first-pass analysis of the data as they arrive at NRL. We are able to generate good quality spectra for each day within about 18 hours of the impact of the last photon on OSSE. The Sun is not available on the OSSE scan plane, so the slewing response to BATSE solar flare triggers is disabled. There have been no slews to the Sun since the last report.