Compton Gamma Ray Observatory Status Report #202 Monday March 10, 1997 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-7 NRA will appear on the World Wide Web very shortly. The URL will be: http://www.hq.nasa.gov/office/oss.htm. Look for NRA 97-OSS-05. Paper copies can be obtained by contacting the CGRO Science Support Center. Proposal due date will be June 12, 1997. The proposal due date, peer-review and timeline meetings are about 2 months behind scehedule relative to previous years, but we are nonetheless confident that Cycle-7 will begin on time. Over 300 abstracts were received in response to the Fourth Compton Symposium call for papers! Don't forget, the early registration deadline is April 1 and hotel registration deadline is April 4. Refer to http://osse-wwwnrl.navy.mil/cgrosymp.htm for details. Recent GI science: A paper entitled "Anisotropic Broad Nuclear Gamma Ray Lines: Application to the COMPTEL Observations of Orion" by B. Kozlovsky, R. Ramaty and R. E. Lingenfelter (Ap J 484, July 20, 1997) can be downloaded from the CGRO WWW site: http://cossc.gsfc.nasa.gov (under the Guest Investigator pages). EGRET EGRET continues to operate normally, and the data deliveries to the archives and to observers is on schedule. The current observations of PKS 0528+134 provide an opportunity to view the Crab and even Geminga at the edge of the field, both of which will be useful in calibrating the performance of the spark chamber. Charged particle analysis indicates that the degradation in performance has been small since the last gas fill. COMPTEL The COMPTEL instrument is performing well and continues routine observations. The COMPTEL operations group has completed all instrument-related preparations for the reboost maneuvers of the CGRO spacecraft scheduled to begin later this month. An initial accelerated processing of the COMPTEL data associated with the recent target-of opportunity observation of Cygnus X-1 has not revealed any strong emission from Cyg X-1 during this period at MeV energies. A further more detailed analysis of these data is currently in progress. A paper has been submitted to Astronomy and Astrophysics on "COMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission" by Collmar et al. A major delivery of both low- and high-level COMPTEL data products to the CGRO public archive at the COSSC, covering the remaining viewing periods of Cycle 4, is anticipated in the near future. A number of abstracts were recently submitted by team members and guest investigators to the organizers of the upcoming 4th Compton Symposium (Williamsburg) and 25th ICRC (Durban). Among the topics to be presented at the Compton Symposium will be a review talk on the diffuse Galactic continuum emission, the latest results on the distribution of 26Al in the Milky Way, spectral properties of the MeV emission from the inner Galaxy, latest COMPTEL results on the Crab and Vela pulsars, as well as a number of additional reports on individual sources. The status of these various scientific projects, as well as team strategies for the upcoming CGRO Cycle 7 proposal round, were discussed at a general team meeting of the collaboration held this past week at the University of New Hampshire. In a break from usual business, team members joined in toasting COMPTEL PI, Volker Schoenfelder, for his recent receipt of the Philip-Morris Research prize for 1997, awarded in recognition of his many contributions to the successful development of the double-Compton telescope technique, and for the exciting discoveries made by the COMPTEL instrument aboard NASA's Compton Observatory. 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 continues to be enabled. One slew occurred during this period, for trigger 6091 on 97/045. There was a 13 degree difference between the on-board and final elevation angles for this event, so that the nominal position was just barely in the scan pattern (2% response at best), though a significant part of the error circle was still covered. The BACODINE position was well covered (43% response). Due to a flight software error the slew observation was only about 40 min long. The error has been corrected. Bursts, flares, and transients through March 2, 1997 have been processed. In the last month, there have been 15 classical GRB triggers. Particle and Cyg X-1 triggers were both higher in this period and there was one solar flare trigger. Since GRO J1744-28 triggers dropped by more than a factor of 5 from last month, BATSE returned to its nominal trigger range on Feb. 25. GRB 970228 was detected by SAX in the GRB monitor and the WFC (IAU Circ. 6572). This event had no corresponding BATSE trigger. The source position reported by SAX was below the horizon for GRO at the time of the burst. By serendipity, OSSE viewed the burst position as part of its scheduled PKS 0528+134 observation. The source rises about 35 minutes after the burst (we also see the source up to about 23 min before the event, when a data gap begins which lasts until source set). Preliminary results from OSSE are included in the following IAU circular. A detailed analysis is still in progress. GRB 970228 (IAUC 6578) S. M. Matz, Northwestern University; K. McNaron-Brown, George Mason University; and J. E. Grove and G. H. Share, Naval Research Laboratory, report on behalf of the OSSE team: "The OSSE instrument on the Compton Gamma Ray Observatory had good exposure to the position of GRB 970228 (IAUC 6572) before and after the burst. We are able to derive limits on flux from the source, starting about 33 min after the event, including the period during which BeppoSAX detected an x-ray source (IAUC 6576). No transient or persistent flux has been detected from about 40 keV to 10 MeV. Preliminary post-burst limits (3 sigma, in units of 10E-5 photons cmE-2 sE-1 keVE-1) at about 40-80 keV are as follows: Feb. 28.149-28.444 UT, 5.3; Feb. 28.473-28.630 (roughly the SAX interval), 8.3; and Feb. 28.149-Mar. 3.000, 2.2. The limit on the flux in the day prior to the burst (Feb. 27.124-28.107) is 3.7 x 10E-5. The source position was not continuously observed during these intervals. The OSSE 40- 80-keV upper limit during the SAX accumulation is comparable to the flux seen by SAX at 2-10 keV. A single power law, consistent with both the SAX observation and the OSSE limits up to 250 keV, must be softer than photon spectral index -0.3." Recent observations are listed in the following table. We have completed a target of opportunity pointing at GX 339-04. A detailed analysis of is currently in progress. 614.5 11-18 Feb GX 339-04 (W.N. Johnson) PKS 2155-304 (public) NGC 7172 (public) 616.1 18 Feb - 18 Mar PKS 0528+134 (W.N. Johnson) MRK 1152 (public) NGC 7314 (public) Low-level OSSE data products through viewing period 507.5 are awaiting delivery to the Compton GRO Science Support Center archive. High-level data products through viewing period 220 have been delivered. 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 GRO J1744-28 is still in outburst. So far from this outburst 2013 bursts have been detected, with 323 triggering the BATSE burst mode. Quick-look results from the BATSE occultation and pulsar monitoring programs are now available over the world-wide-web. Recent occultation results my be found at: http://www.batse.msfc.nasa.gov/data/occult . Recent pulsar flux and frequency information, including plots for the last 100 days, are located at: http://www.batse.msfc.nasa.gov/data/pulsar . During the last month the following pulsed sources have been detected by the BATSE pulsed source monitor: GRO J1744-28, Her X-1, Cen X-3, 4U 1626-67, OAO 1657-415, EXO 2030+375, Vela X-1,and GX 301-2. The burst trigger has returned to using rates from channels 2+3 (50 - 300 keV), with thresholds of 5.5 sigma for all timescales. As of March 7 BATSE has detected 1750 gamma-ray bursts out of a total of 6011 on-board triggers in 2145 days of operation. There have been 781 triggers due to solar flares, 39 due to SGR events, 64 due to terrestrial gamma-ray flashes, and 1800 due to the bursting pulsar GRO J1744-28.