Compton Observatory Science Report #128 Thursday, July 15, 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. Science operations are continuing. There was a maneuver performed on Tuesday, July 13, 1993, to the attitude of period 228. The change in the Z-axis was very small (about 2 degrees). The eigenaxis maneuver angle was 14 degrees, with maneuver times 1327Z to 1337Z. The HGA boom axis with respect to the equator is now 75.6 degrees. The Z-axis target is SN1993J, and the OSSE X-axis target is the Vela Pulsar. Based on the number of packets of data delivered to instrument teams from PACOR, the percentage of fulltime coverage achieved with 32Kbps realtime data between June 30 and July 5 was 87 percent. As of July 11, 1993 the Compton GRO mean orbital altitude was 352.99 km. BATSE ----- During viewing period 228 BATSE folded-on-board pulsar data will be collected for the Crab pulsar, Geminga, PSR 0611+22, PSR 0656+14, Her X-1, PSR 1508+55, PSR 1919+21. As of July 14rd, BATSE has detected 709 cosmic gamma-ray bursts out of a total of 2341 on-board triggers in 813 days of operation. There have been 663 triggers due to solar flares with emission above 60 keV. COMPTEL ------- The COMPTEL instrument is performing well and continues routine observations. The collaboration will be well represented at the upcoming International Cosmic Ray Conference in Calgary, with a total of 13 presentations on recent research results, in addition to the special evening session on the Compton Observatory. The COMPTEL team has also recently submitted a number of abstracts for the Compton Symposium in September, which will include 3 invited, 6 oral contributed, and 3 poster presentations by team members. In related news: as the Tour de France winds its way through the Alps, the peloton seems to be watching Indurain from an (ever-increasing) distance; Fignon is patiently biding his time. EGRET ----- EGRET operations were normal this week. Interactions with Guest Investigators and scientists involved with us in cooperative work continues at a healthy level. As noted last week, we are currently in the middle of a four-week viewing period which will allow a longer exposure than has been possible recently, although the data collection is well below that before the tape recorder failure. Neil Gehrels, Jay Norris and I (Carl Fichtel) have been reading and sorting the abstracts for the Second Compton Symposium. We were pleased at the number of the abstracts received and the potentially interesting nature of the talks. We are looking forward to the symposium and seeing all of you there. OSSE ---- OSSE operations are normal. In viewing period 228, the Z-axis target is the recent supernova SN 1993J, and the X-axis target is the Vela pulsar (PI team). During those portions of the orbit in which both targets are visible, we have assigned viewing priority to the supernova; thus the pulsar is receiving only a small amount of livetime. During the significant portion of the orbit during which neither target is visible, engineering data are being collected to improve our calibration of the neutron v. gamma ray pulse shape discrimination efficiency. Because the Sun is not available on the OSSE scan plane, the slewing response to BATSE solar flare triggers is disabled. OSSE data from viewing period 10 will be delivered to the Compton GRO Science Support Center Archive today. During that viewing period, the targets were N Mus 1991 with the galactic plane near (l,b) = (300,0) and 3C 279. Some OSSE preprints/reprints arriving recently at the SSC include: "OSSE Observations of NGC 4151", M. Maisack et al, ApJLett 407, L61, 1993. "The Oriented Scintillation Spectrometer Experiment: Instrument Description", W.N. Johnson et al, Ap.J.Supp., 86, 693, 1993. (Note that EGRET and COMPTEL Instrument Description papers also appeared in this ApJ Supplement.) "Gamma-Ray and Radio Observations of PSR B1509-58", M.P. Ulmer et al, ApJ, in press. "OSSE Observations of Galactic 511 keV Positron Annihilation Radiation: Initial Phase 1 Results", W.R. Purcell et al, ApJLett, in press. "OSSE Observations of the 4 June 1991 Solar Flare", R.J. Murphy et al, to appear in the Proceedings of the 23rd International Cosmic Ray Conference.