Compton Gamma Ray Observatory Status Report #188 Friday December 8, 1995 Questions or comments can be sent to Chris Shrader at the CGRO-SSC. Phone: 301/286-8434 e-mail: shrader@grossc.gsfc.nasa.gov Guest Investigator News The Cycle-6 NRA release is imminent! The document and its appendices are currently going through approval cycle at Goddard, after which it will be sent for final review by the Program Scientist. A December 22, 1995 release, with a March 22, 1996 proposal due date is now the most likely scenario. As soon it is formerly approved, the NRA will be mailed out, and made available electronically (through the GRO-SSC WWW site at http://cossc.gsfc.nasa.goc/cossc/cossc.html; or GRONEWS, grossc.gsfc.nasa.gov, gronews). The current Target of Opportunity re-orientation of the space craft (refer to the BATSE report below) was a yaw-only maneuver, and thus does not effect any COMPTEL or EGRET integrations. The CGRO Exhibit at the Natinal Air and Space Museum is scheduled to open on JANUARY 9, 1996. It consists of a 6-minute video on CGRO, and still visuals and text describing scientific highlights of the mission. It will be on display through the summer of 1996 in the "Milestones of Flight" hall of the museum. EGRET EGRET operations were normal this monthly period. Delivery of the final phase 3 data to the GRO SSC has been completed on schedule, and delivery of the phase 4 preliminary data to the GRO SSC is also on schedule. Interaction with guest investigators continues at a good level. During the period from October 31, 1995 to November 28, 1995, EGRET was turned off to conserve the remaining spark chamber gas while observations were being made which were of primary interest to those using the other instruments on GRO. On November 28, EGRET was activated and is currently pointing in the direction defined by (l=77.44 degrees, b=-38.58 degrees). There was a rotation about the z axis on December 6 for a target of opportunity, but that did not effect the collection of EGRET data for this region. Starting on December 12, EGRET will be observing the region centered on (l=5.50 degrees, b=-0.17 degrees). Scientific papers on bright supernovae remnants and the pulsar B9656+14 have been accepted by the Astrophysical Journal, and an article on the evolution of gamma-ray loud active galactic nuclei has appeared in the Astrophysical Journal. COMPTEL The COMPTEL operations group reports that an ADC in COMPTEL's Remote COMPTEL Interface Unit-A (RIU-A), external to the instrument itself on the spacecraft platform, failed on 24 November. This ADC provides a monitor to the POCC at NASA/GSFC of COMPTEL detector assembly temperatures and power supply voltages. A similar failure occurred in March 1994 for COMPTEL's RIU-B. Independent COMPTEL instrument telemetry continues to provide the relevant experiment state-of-health information without problem. There has been no interruption to the flow or quality of COMPTEL's scientific data. Operations procedures have been adjusted to compensate for this loss of monitoring capability. A number of additional gamma-ray bursts have occurred within the field of view of COMPTEL since the last report (GRBs 951117, 951119, 951128, 951202, and 951208). Once again, none of these was detected at MeV energies by COMPTEL. The last burst detected within the field of view of COMPTEL occurred in May 1995, establishing a new record (of sorts) for the longest period without a burst detection by the telescope. Since May 1995, the COMPTEL burst group has responded to a total of 25 BATSE/BACODINE triggers with locations falling within the COMPTEL field of view; typical response times are now on the order of 15 minutes after a BATSE trigger. Procedures are currently being implemented to further reduce this response time to approximately 3 to 5 minutes following receipt of a burst trigger message. A new release of COMPTEL data to the CGRO public archive is scheduled for the near future. This release will include both low- and high-level data products, in anticipation of the CGRO Cycle 6 proposal cycle. OSSE OSSE operations are normal. The instrument is working as designed, with all subsystems in complete and full operation. The slewing response to BATSE burst triggers has been enabled since 30 June. OSSE 2 minute spectral data products are being reprocessed to fix miscalculations in ODS data (data stored on-board during TDRSS realtime outages) beginning with viewing period 211. The corrections affect some medium and high range livetimes and some spectral channel counts during approximately 1% of a typical day of data. Recent observations are listed in the following table. View period Dates Target (owner) 503 14-21 Nov N Ecliptic Pole Survey (PI team) M 31 (not assigned) NGC 5506 (not assigned) 504 21-28 Nov N Ecliptic Pole survey (PI team) M 31 (not assigned) 507 28 Nov - 8 Dec CTA 102 (not assigned) GRS 1915+105 (PI team) NGC 5506 (not assigned) (A slight yaw was approved for this viewing period to give OSSE a better view of the recurring x-ray transient source GRS 1915+105). Last month it was reported that viewing period 502 targets included Geminga, NGC 3227, NGC 4388, M 87, and NGC 1068. NGC 1068 was not observed during this viewing period. Data through viewing period 338 have been delivered to the Compton GRO Science Support Center archive. BATSE The following notices appeared in IAU Circular 6266: GRS 1915+105 B. A. Harmon, W. S. Paciesas, S. N. Zhang and K. J. Deal, NASA/Marshall Space Flight Center, report, for the Compton Observatory BATSE Team: "Hard x-ray flux (20-100 keV) from GRS 1915+105 has increased over the past month to a level comparable to the intense outbursts seen in 1992 and 1994 (IAUC 5590, 5959). The flux reached 300 mCrab around Oct. 15 and has remained near this level (within 50 percent) as of Nov. 20. Less intense outbursts reaching about 200 mCrab have also been observed since June 1995. These are nonperiodic but are of similar intensity and each about 15-20 days in duration. The source continues to be variable on a daily basis. The hard x-ray activity correlates well on long timescales (days to weeks) with the radio flux, but no strong signature is seen in x-rays that corresponds to the shorter- timescale (hours to days) radio flares reported below." 4U 0115+634 M. H. Finger, M. Scott and K. Hagedon, Universities Space Research Association; R. B. Wilson and C. A. Wilson, NASA/Marshall Space Flight Center; M. Stollberg and W. S. Paciesas, University of Alabama, Huntsville; and T. A. Prince and B. Vaughan, California Institute of Technology, report for the BATSE/Compton GRO Observatory pulsar team: "Pulsed hard x-ray flux is currently being detected from the transient x-ray pulsar 4U 0115+634. The source was detected on Nov. 18, when the rms pulsed flux (20-50 keV) was approximately 15 mCrab. This is the first detection by BATSE of this source since the outburst that occurred during 1994 May 8-June 27 (IAUC 5990, 5999). On 1995 Nov. 21 the rms pulsed flux (20-50 keV) was approximately 70 mCrab. The pulse frequencies observed from Nov. 19 to 21 are consistent with a neutron- star spin rate of 0.2766635 +/- 0.0000003 Hz at epoch JD 2450042 and a spin-up rate of 1.4 +/- 0.3 x 10E-11 Hz/s, using the binary orbital ephemeris of Cominsky et al. (1994, 2nd Compton Symposium, AIP Proc. 304, 294)." Currently an unusual source near the galactic center region is being detected. The source has a soft spectrum and is not detected above 50 keV. Efforts are underway to determine the source location. A spacecraft re-orientation was requested and granted in order to improve BATSE's source location sensitivity. During the past 30 days (TJD 10028 - 100058) the following pulsed sources have been detected by the BATSE pulsed source monitor: Her X-1, 4U 0115+634, Cen X-3, 4U 1626-67, OAO 1657-415, GX 1+4, Vela X-1, and GX 301-2. As of December 6th BATSE has detected 1425 gamma-ray bursts out of a total of 3828 on-board triggers in 1688 days of operation. There have been 766 triggers due to solar flares, 10 due to SGR events, and 51 due to terrestrial gamma-ray flashes.