Compton Gamma Ray Observatory Status Report #199 Tuesday, December 10, 1996 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 A draft of the Cycle-7 NRA has been sent to NASA Headquarters for final editing and bureaucratic approval. We anticipate a February 1997 issue and a May 1997 proposal due date. Significant policy changes for Cycle-7 include a reduction in the proprietary period for observational data, a reduction in proposal page limits, and changes in the grant eligibility requirements for Instrument Team members. The total budget for Cycle-7 grants is expected to be about 75% of the Cycle-6 total. Optimal exposure times for OSSE targets may be longer in cycle 7 than in past cycles due to the anticipated higher background levels with the observatory in a 500-km orbit. We anticipate allocating approximately 16-20 weeks of EGRET observing time in narrow field-of-view mode. BATSE "quick-look" flux reports will be made public promptly, as will data resulting from unproposed ToOs or serindipitous discoveries. The second announcement for the forthcoming 4th Compton Symposium has been issued. The Symposium will be held in Williamsburg Virginia on April 27-30, 1997. The abstract deadline is February 15, 1997. For more information refer to the URL: http://osse-www.nrl.navy.mil/cgrosymp.htm on the World Wide Web. Instrument Team Reports EGRET EGRET operations were normal this monthly period. Delivery of the final phase 4 data to the GRO SSC was completed on schedule, and delivery of the phase 5 preliminary data to the GRO SSC is also on schedule. Interaction with guest investigators continues at a good level. The major paper on the details of the high-energy gamma-ray Galactic diffuse radiation and its interpretation by Hunter et al. has been accepted by the Astrophysical Journal. Preprints will be available and distributed in the near future. A paper on the study of the high-energy gamma-rays from the Sun has been submitted to the Astrophysical Journal; the results suggest that either solar particle acceleration continues for many hours, or there is a trapping region wherein energy losses are very low. EGRET will be reactivated on December 10, 1996 to begin a lengthy observation of 3C 279. Finally, here is a personal note from Carl Fichtel. "In consideration of the position that I have reached in my career including the fine results that have come from EGRET and my desire to spend more time enjoying the worlds of art, literature, gardens, and music, it seems a good time to step forward into retirement while I can still hope for a reasonable number of years of good health. I have been planning the transition of my work here both on EGRET and in the Laboratory for High Energy Astrophysics as a whole, and I believe the change should be a smooth one. Klaus Pinkau will automatically become the sole Princiapal Investigator of EGRET by the agreement with NASA headquarters long ago. Dave Bertsch will be the routine NASA contact. "I shall certainly continue to be interested in learning of the new scientific results of fundamental significance which are expected to be forthcoming. I shall also enjoy continuing to see my many friends from time to time as the opportunity arises. "I wish you all health and happiness. "Carl Fichtel" COMPTEL The COMPTEL instrument is performing well and continues routine observations. A systematic reprocessing and inspection of recent COMPTEL data taken around the times of gamma-ray bursts occurring within the field of view of the instrument has uncovered evidence for COMPTEL detections of an additional 1-2 GRBs previously missed in quick-look processing. A more detailed analysis of the data associated with these events is currently in progress. A paper on "New COMPTEL results on MeV gamma rays from the Orion/Monoceros region" (Bloemen et al.) is currently in press in the Astrophysical Journal (Letters). A general team meeting of the collaboration was held at ESA/ESTEC in The Netherlands from 19-22 November. At the upcoming 18th Texas Symposium on Relatvistic Astrophysics later this month there will be presentations on the latest COMPTEL results relating to the cosmic diffuse gamma-ray background at MeV energies (by Kappadath et al), gamma-ray bursts (Connors et al), 44Ti line-emission from the Cas A supernova remnant, and unidentified high-latitude sources detected by COMPTEL (the last two by Iyudin et al). And, at the 189th meeting of the AAS in Toronto, there will be reports on gamma-ray bursts (Connors et al.), solar studies (Rank et al, Young et al), and an all-sky search for 2.2-MeV line emission from astrophysical sources (McConnell et al). OSSE OSSE operations are currently normal. The instrument is working as designed, with all subsystems in complete and full operation. The slewing response to BATSE burst triggers is currently enabled, but it was disabled from 26 Nov to 5 Dec to protect against slews from outbursts of the soft repeater SGR 1806-20, which was active and on the scan plane. Bursts, flares, transients, and SGRs through 2 Dec 1996 have been processed. In the last month, 10 classical GRB triggers occurred, of which 3 produced significant responses in the shields. None produced a significant response in the central detectors. The 10 solar flares were relatively weak C and B class events with no clear prompt signal in the OSSE shields or central detectors. The TGF (trigger #5665) was seen in the shields. None of the 16 triggers from the SGR produced an obvious signal in the shields or central detectors. There was one triggered slew during this period, for #5672, and SGR burst. While the slew put OSSE at the proper scan angle, the burster was out of the field of view in the transscan direction. The new bursts are available on the WWW at http://www.astro.nwu.edu/astro/osse/bursts/newlist.html "Time Variability Detected in the Gamma-Ray Emission of 3C 273 by OSSE" by K. McNaron-Brown et al. has been accepted for publication. It will appear in the 10 Jan 1997 issue of ApJ Letters. It reports faster time variability and greater luminosity in the OSSE band than previously observed. While no spectral variability is detected, the spectral break occurs at 300(+-100) keV, significantly lower than the break at ~1 MeV reported by Johnson et al. (1995) from 1991 June data. Recent observations are listed in the following table. We are in the middle of a long series of pointings designed to map the annihilation radiation and hard X-ray continuum in the area surrounding but not including the galactic center. This should nicely complement observations made in earlier Cycles. View period Dates Target (owner) 602 12-19 Nov GAL 353.6+10.7 (W.R.Purcell) [no 2nd science target, engineering test] 603 19-26 Nov GAL 356.2+06.4 (W.R.Purcell) [no 2nd science target, engineering test] 605.1 26 Nov - 3 Dec GAL 006.2-10.8 (W.R.Purcell) Arp 220 (public) 604.1 3-10 Dec GAL 003.7-06.5 (W.R.Purcell) Mrk 231 (public) Arp 220 (public) Low-level OSSE data products through viewing period 427 and high-level data products through viewing period 220 have been delivered to the Compton GRO Science Support Center archive. In addition, by special request all subsequent public Cyg X-1 data sets, both low and high level, have been delivered. Refer to the CGRO-SSC page on the WWW (http://cossc.gsfc.nasa.gov), or contact Tom Bridgman (bridgman@grossc.gsfc.nasa.gov) for more information. BATSE The following items were reported in IAU circular 6512: SGR 1806-20 K. Hurley, Space Sciences Laboratory, University of California, Berkeley, on behalf of the Ulysses Gamma-Ray Burst Team; C. Kouveliotou, Universities Space Research Association and Marshall Space Flight Center (MSFC), NASA; G. J. Fishman and C. A. Meegan, MSFC; and J. van Paradijs, University of Amsterdam and University of Alabama, Huntsville, report: "We have derived a much-refined position for the transient soft-gamma-ray repeater reported on IAUC 6501, via triangulation between Ulysses and BATSE of two bursts on Nov. 19. The position is an annulus whose radius is 76o.990, whose halfwidth is 0.0092 deg (3-sigma confidence level), centered at R.A. = 23h55m34s.9, Decl. = -30 55'55" (equinox 2000.0). The combined triangulation annuli and BATSE error circles give error boxes whose areas are more than a factor of 100 smaller than the BATSE error circles alone. They are consistent with the known position of SGR 1806-20 (Murakami et al. 1994, Nature 368, 127), and the two annuli midlines pass within 4" of this position. We conclude that the source of these bursts, as well as of the ones that have occurred since Oct. 30, is indeed SGR 1806-20. The latest short, soft event from this source was detected with BATSE on Nov. 23, so continued monitoring at other wavelengths is strongly encouraged." The following was reported in IAU circular 6514: GRO J2058+42 C. A. Wilson, NASA Marshall Space Flight Center; T. Strohmayer, NASA Goddard Space Flight Center and Universities Space Research Association; and D. Chakrabarty, Massachusetts Institute of Technology, report: "The Compton Observatory/BATSE instrument has observed a series of five outbursts from the 195.6-s accreting x-ray pulsar GRO J2058+42, with a bright initial outburst in Sept. 1995 (IAUC 6238) followed by four weaker (15-20-mCrab pulsed flux in the 20-50-keV band) outbursts, all spaced by about 110 days. The weak outbursts have each lasted about two weeks, with a marginal decline in peak intensity over consecutive outbursts. The most recent outburst peaked on 1996 Nov. 25 +/- 2 with a 20-50-keV pulsed flux of 14 +/- 1 mCrab. The barycentric pulse frequency on Nov. 25.0 UT was 5.1125 +/- 0.0001 mHz. A target-of-opportunity scan of the Compton/OSSE/BATSE error box (IAUC 6239) on Nov. 28 with the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer (RXTE) constrained the 90-percent-confidence region for the source position to a circle with 4' radius and centered at R.A. = 20h59m.0, Decl. = +41d43' (equinox 2000.0). RXTE/PCA observed a peak flux of 11 +/- 1 mCrab (2-30 keV) and a pulse frequency consistent with the BATSE measurement. Optical observations of the new error circle are strongly encouraged in order to identify the optical companion, most likely a Be star." The following report has been submitted for inclusion in an IAU Circular: GAMMA-RAY BURSTS C. Meegan, V. Connaughton, G. Fishman (NASA/MSFC), R. M. Kippen (UAH), C. Kouveliotou (USRA), K. Hurley (UC Berkeley), T. Cline, D. Palmer, S. Barthelmy, P. Butterworth, B. Teegarden, H. Seifert, J. in 't Zand (NASA/GSFC), E. Mazets, S. Golenetskii (IOFFE) report: Several spacecraft have detected a sequence of gamma-ray bursts over a two day period whose locations are consistent with a single source. The following table gives the times of the events, the BATSE determined location with its statistical uncertainty, an approximate duration, and the spacecraft that detected the event. Date Time BATSE ULYSSES WIND UT sec) RA DEC ERR DIST DUR TGRS KONUS (degrees) (sigma) (sec) 961027 42247 67.4 -42.4 5.6 1.4 100 no no no 961027 43322 68.7 -54.3 5.8 3.0 0.9 no no yes 961029 23677 59.4 -52.6 4.6 1.0 30 no no yes 961029 24350 59.8 -48.9 0.3 750 yes yes yes The DIST column shows the proximity (where sigma is the quadrature sum of the statistical errors and does not include BATSE's ~1.6 deg systematic error) of the first three BATSE event locations to the fourth which has the best determined position, including Interplanetary (IPN) locations using BATSE, Ulysses and Konus. The Ulysses-BATSE IPN annulus is described by a center at RA=356.657 and DEC=-31.408 (J2000) with a radius of 49.883 deg, full width 0.078 deg. The much wider Ulysses-Konus annulus defines the end-points of the Ulysses-BATSE annular segment at RA=59.73, DEC=-47.07 and RA=60.32, DEC=-52.58 with a 99.7% confidence level. A soft gamma repeater (SGR) can be excluded as a common source by the durations of the events, as well as by their spectra, which are consistent with classical gamma-ray bursts. The temporal structures of the events are quite different, apparently ruling out a gravitational lens interpretation. The third and fourth events are very probably separate triggers from a single burst, making the combined event the longest burst (1420 sec) ever seen in this energy range. Although a posteriori calculations are problematic, the probability of such a temporal and spatial coincidence of four unrelated events is low. On November 28, 1996, a single event upset occurred in the BATSE flight software memory. This event occurred when GRO was in the central part of the SAA. This altered an instruction that was part of the code for outputting burst data. When the next burst trigger occurred, on November 29, this instruction was executed, causing the program to hang. As designed, a watchdog timeout occurred, reloading and starting the default version (Rev. 0) of the flight software from ROM. The reload caused a spurious burst trigger. The default software was not executing a valid output schedule, so pulsar data were lost over the next 2 days before getting back to a normal configuration (Rev. 7). However, continuous data, discriminator data, and burst data were useable, though not optimum, during this period. On November 30, two attempts were made to send commands to return BATSE to the desired configuration. Both times, when Rev. 2 was loaded, there was a watchdog timeout and a reset to Rev 0. It was determined that the original crash could have corrupted the output schedule that Rev. 2 uses. On Dec. 1, this output schedule was reloaded, and Rev. 2 was reloaded without incident. The later revisions were then loaded, and BATSE returned to nominal operations. The loss of data is estimated as approximately 25% over a period of 3 days. The BATSE team is grateful for the excellent cooperation of the FOT in resolving this problem. During the last month the following pulsed sources have been detected by the BATSE pulsed source monitor: Her X-1, Cen X-3, 4U 1626-67, OAO 1657-415, Vela X-1,and GX 301-2. The burst trigger continues to use rates from channels 1+2 (20 - 100 keV), with thresholds of 5.5 sigma for 64ms and 256ms timescales and 7.0 sigma for the 1.024s timescale. As of December 4 BATSE has detected 1699 gamma-ray bursts out of a total of 5601 on-board triggers in 2052 days of operation. There have been 778 triggers due to solar flares, 31 due to SGR events, 64 due to terrestrial gamma-ray flashes, and 1477 due to the bursting pulsar GRO J1744-28.