Compton Observatory Science Report #134 Thursday, September 9, 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. There were two maneuvers performed on Tuesday, September 7. The first was to the attitude for the OATS burn test, to align the thrust vector with the orbital velocity vector at a quarter orbit after noon. The times were 1409Z to 1440Z; the angle was 101.16 degrees, and the ending HGA boom- equatorial plane angle was 12.36 degrees. The second maneuver was to the attitude of period 302.0. The times were 1843Z to 1927Z, with an angle of 153.3 degrees, and a final HGA boom-equatorial plane angle of 29.44 deg. The thruster test was done to verify the response of the spacecraft body to thruster firings and the stability of the planned attitude control algorithm. The results are being studied. Options for the reboost scenario are being studied intensively. The (very tentative) starting date for the reboost is now October 4. As a result of the rise in intensity of the source GX 1+4 (see BATSE report below), and because there is a selected GI investigation to observe this object as a target of opportunity, this was declared a target of opportunity this week, and a maneuver was done on Thursday, September 9. The maneuver times were 1322Z to 1349Z; the maneuver angle was 89.75 degrees, and the current HGA boom-equatorial plane angle is 34.8 degrees. The attitude is Z-Axis: ra = 258.635 dec = -22.697 X-Axis: ra = 180.209 dec = +25.626 Z-Axis: l2 = 1.410 b2 = 9.262 X-Axis: l2 = 217.630 b2 = 78.573 The OSSE secondary target is a Virgo region study at galactic (298,+82) (key project). The viewing period will be numbered 302.3. The proposal called for a two week observation, however, the investigators have agreed that if the intensity falls below threshold before that time the normal viewing program could resume. ARCHIVES -------- The COSSC archive is operating normally with no scheduled down-time. Archive contents- Burst to trigger 884, four months of daily HER and SHER data. Comptel - Period 1, 4, and 13 Egret - Periods 0.2-30 are available (Maps and photon lists) OSSE - Periods 0.2-11 are available (SDB data) BATSE ----- The following was submitted as an IAU Circular: GX 1+4 M.H. Finger (Computer Sciences Corporation), R.B. Wilson, G.J. Fishman (NASA/MSFC), L. Bildsten, D. Chakrabarty, and T.A. Prince (Caltech) report for the BATSE/Compton Gamma Ray Observatory team: "Beginning August 27th, the x-ray binary pulsar GX 1+4 has dramatically brightened in the hard (>20 keV) x-ray band. The pulsed flux is now the highest seen by BATSE in more than two years of monitoring. On September 5th the barycentric pulse period was 120.567 +- 0.005 seconds, and the phase averaged pulsed flux (20 to 120 keV) is well fit with F(E) = (A/E)exp(-E/kT) with kT = 27+-3 and F(50 keV) = (2.1 +- 0.1) x 10**-4 photons/cm2-s-keV. The period derivative has increased steadily from 1.2+-0.4 s/yr as measured in March 1993 to the current rate of 3.7 +-0.3 s/yr. The cause of the GX 1+4 outbursts is not known, but may be due to variations in the M6-III red giant companion V2116 Oph (V=19, R=15, k=8, finder in Nature, 270, 586)." During viewing period 302.2 BATSE folded-on-board data will be collected for PSR 0540-693, the Crab pulsar, and Her X-1. As of September 6th, BATSE has detected 761 cosmic gamma-ray bursts out of a total of 2411 on-board triggers in 860 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 were scheduled to begin on Thursday this week. During the recent test of the spacecraft propulsion system, the primary detector high voltages of COMPTEL were once again turned off as a safety precaution; the experiment was reactivated without incident immediately following. The collaboration toasted the completion of the remaining Phase 2 observations earlier this week, and looks forward to continuing successful operation during the Phase 3 observing cycle. EGRET ----- EGRET operations were normal this week. The new procedures associated with source allocations begun for Phase 3 are being implemented; however, additional definitions and clarifications are needed. If these are provided at the forthcoming User's Committee Meeting, it should be possible to meet the optimum schedule, except, of course, for the early 301 observation. Even there, we should come close unless the User's Committee decides on rules grossly different from those anticipated to be enacted. We are now beginning the reviews of the results to be presented at the Second Compton Symposium, and are hopeful that the others at the meeting will be as enthusiastic as we are. OSSE ---- OSSE operations are normal. We are currently in a target of opportunity pointing, the first driven by an approved Guest Investigation. For the current target of opportunity viewing period, the Z-axis target is the X-ray binary GX 1+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 GX 1+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. 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. For the brief period before the target of opportunity was declared, the Z-axis target was N Cyg 92 (GI: S. Starrfield), and the X-axis target was NGC 5548 (GI: R. Petre). Data from viewing periods 12 and 13.0 have been fully screened and are ready to be delivered to the Compton GRO Science Support Center Archive. Targets during vp 12 were Cen A, NGC 5548, Mrk 668, and 3C 390.3. Targets during vp 13.0 were the galactic plane at 25 deg longitude and NGC 5548.