Compton Observatory Science Report #124 Thursday, June 17, 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. The following message is from the GRO Operations Team: The final phase of the GRO orbit reboost operation began on June 15 and was expected to continue for approximately two weeks. On June 15, a reaction-wheel attitude maneuver was performed to align the thrust vector with the orbital velocity vector. In the afternoon, the four B-side attitude control thrusters were successfully fired during the first 16-minute window. One orbit later, near the beginning of the second 16-minute window, the firing of the thrusters drove the spacecraft attitude rates out of the specified limits. This caused the spacecraft to go into a safe mode; however, the rates exceeded those that could be controlled by the reaction wheels. The spacecraft was then switched to the standby mode, and the thrusters were fired manually, which reduced the momentum. The spacecraft was then commanded to the sun referenced pointing mode and it is now stable. Reboost operations are suspended while data is being analyzed. Later analysis appears to indicate that one of the four thrusters was not producing its full thrust, causing an imbalance. Several fallback scenarios are possible, and are being considered. It is not yet certain whether science operations will be resumed soon while the problem is studied, or whether tests will continue. BATSE ----- During the reboost BATSE folded on board data is being scheduled for collection for the Crab Pulsar, PSR0540-693, Her X-1 and PSR 1951+32. As of June 15th, BATSE has detected 683 cosmic gamma-ray bursts out of a total of 2291 on-board triggers in 784 days of operation. There have been 652 triggers due to solar flares with emission above 60 keV. COMPTEL ------- The COMPTEL operations group reports that the instrument was placed in a "safe" configuration late Monday 14 June, with the high voltages to all primary detector modules turned off, in preparation for the orbital reboost of the GRO spacecraft. COMPTEL will remain in this safe mode for the planned two-week duration of the reboost maneuver. Routine deliveries of flight data to the COMPTEL group at the Max Planck Institute are suspended as of 15 June, and will resume when the orbital reboost is complete, with the maneuver to begin observing period 227. Meanwhile, normal state-of-health monitoring of COMPTEL, mostly thermal control, continues from the University of New Hampshire. EGRET ----- EGRET operations were normal this week. At the moment the instrument is off due to the orbit reboost operation. The several presentations at the American Astronomical Society last week created considerable interest, particularly those on the galactic plane and the AGN's. There was considerable guest investigator and visiting scientist activity here this week; we somehow managed to find everyone a desk and a terminal. Next week, we should be back to the normal visitor level. OSSE ---- For the reboost period (viewing period 225), OSSE is in Science Mode for roughly half of each day. Three detectors are attempting a measure of the diffuse low-energy gamma ray background, while the fourth performs engineering tests. On day 93/168 (Thursday UT morning), the elevation drive for detector 4 went off-line after a positioning error. The drive was recalibrated and returned to science operations after about 7 hours. We are continuing to study the data, but it appears that as the detector was commanded to a position near its end of travel in the negative scan direction the main positioning potentiometer became noisy. We commanded the drive away from its limit switch, and the noise disappeared. The subsequent recalibration of the drive moved the detector to a position nearer its limit switch without incident. The drive is once again operational. A similar problem occurred for detector 3 in viewing period 1, and it has not recurred. Data from the activation period, days 91/105-91/118, have been delivered to the Compton Observatory Science Support Center for archiving. Targets during this time were the Sun and the Crab Nebula and Pulsar. Other Items: ------------ Reminder on Call for Papers for the Second Compton Symposium We include here the list of invited speakers and topics for the Second Compton Symposium, to be held at the University of Maryland Conference Center on September 20-22, 1993. If you need the Information Request Form or the Abstract Form, contact the Science Support Center by phone or e-mail (Ms. Sandra Barnes, 301-286-7780, barnes@grossc.gsfc.nasa.gov). The regular registration fee is $160. A special registration fee of $60 will be available for students, and registrations after September 1 will be $200. Note that abstracts are due by July 1, 1993. On July 1, the conference managers Jorge Scientific Corp. will be mailing out a logistics package containing registration form, hotel listings, shuttle service information, etc. to all those who have requested more information. SECOND COMPTON SYMPOSIUM Invited Speakers Introductions by Neil Gehrels, James Trainor, and University of MD (?) SOLAR AND BURST SUMMARIES Compton Observatory Solar Flare and Neutron Measurements, James Ryan Gamma-ray Bursts: Observational Overview, Gerald Fishman Gamma-ray Burst Models: Present Problems and Possible Solutions, Alice Harding GALACTIC SOURCES Energetic Radiation from Spin-Powered Pulsars, David Thompson Timing Irregularities in Pulsars, Joseph Taylor Accreting Neutron Stars, Thomas Prince Supernova Puzzles and Gamma Ray Astronomy, Donald D. Clayton BATSE Observations of Transient Hard X-Ray Sources, Alan Harmon Quasi-Periodic Oscillations of Hard X-Ray Transients Observed with BATSE, Chryssa Kouveliotou TBA, Michael Hillas CENTRAL GALACTIC REGION OSSE Observations of Galactic Positron Annihilation Radiation, William Purcell Galactic Nucleosynthesis Measurements Through 26Al, Roland Diehl Multiwavelength Approach to Gamma-ray Sources in the Galactic Center Region, Felix Mirabel Particle Acceleration and Gamma-ray Emission by Low-mass X-ray Binaries, Fred Lamb COSMIC RAYS AND GALACTIC DIFFUSE RADIATION Galactic Cosmic Rays, Vladimir Ptuskin Diffuse Continuum Emission from the Galaxy, Andrew Strong ACTIVE GALACTIC NUCLEI The Canonical Seyfert Spectrum: The Implications of OSSE Observations, Neil Johnson Models of Gamma Rays and X-rays from Non-beamed AGNs, Andrzej Zdziarski EGRET Observations of AGN's, Robert Hartman Variability of EGRET-Detected AGN's and Acceleration Mechanism, Peter Michelson Non-thermal Gamma-ray Emission from Blazars, Alan Marscher Timeline: The GRO Timeline for the remainder of Phase 2 (Not including any changes created by the reboost anomaly this week) follows. This does include the changes to observe SN 1993J this summer. VIEW +Z-AXIS GRO Z-AXIS GALACTIC GRO X-AXIS OSSE PRIMARY TARGET OSSE SECONDARY TARGET PER. START TARGET RA DEC LONG LAT RA DEC TARGET RA DEC TARGET RA DEC 227 06/28/93 GAL 355+05 258.44 -30.35 355.00 5.00 189.52 31.57 G CENTER 0+0 266.40 -28.94 COMA CLUSTER 194.90 27.96 228 07/06/93 SN 1993J 143.64 65.00 148.11 41.22 116.97 -22.62 SN 1993J 148.84 69.02 PSR 0740-28 115.71 -28.38 229 07/20/93 SN 1993J 145.33 63.18 149.85 42.69 131.74 -26.16 SN 1993J 148.84 69.02 VELA PULSAR 128.92 -45.18 230 08/03/93 VELA PULSAR 129.38 -48.16 266.17 -4.28 121.03 41.53 VELA PULSAR 128.92 -45.18 MRK 78 115.67 65.18 231 08/10/93 GAL 5+05 264.60 -22.06 5.00 5.00 188.59 30.82 G CENTER 0+0 266.40 -28.94 COMA CLUSTER 194.90 27.96 232 08/17/93 NGC 6814 289.94 -15.33 22.22 -13.08 186.93 -39.38 NGC 6814 295.67 -10.31 NGC 4507 188.90 -39.91 233.1 08/25/93 GAL 348+00 258.02 -39.35 347.50 0.00 188.46 23.07 GPLANE 347.5 258.02 -39.35 MRK 421 166.11 38.21 233.2 08/31/93 GAL 348-06 265.01 -42.18 348.10 -5.97 193.05 18.87 GPLANE 347.5 258.02 -39.35 MRK 421 166.11 38.21 09/07/93 End Phase 2