Compton Observatory Science Report #181, Tuesday, May 9 1995 Chris Shrader, Compton Observatory Science Support Center Questions or comments can be sent to the CGRO SSC. Phone: 301/286-8434 e-mail: NSI_DECnet: GROSSC::SHRADER Internet: shrader@grossc.gsfc.nasa.gov Guest Investigator News Some of you have probably noticed that this is the first CGRO status report in a little over one month - this is because the biweekly status report is now the monthly status report! Subsequent reports will be issued by the 10'th of each month. Issues of sufficient urgency may be distributed in the interims via this e-mail exploder. A total of 229 Guest Investigator proposals were submitted for Cycle 5! This is very similar to last year (236). The over-subscription rates for observing time on the pointed instruments range from about 3:1 to 4:1. The peer-review will be held later this month, and the timeline committee will meet the week of June 26, 1995. We thus hope to notify Guest Investigators of the fate of their proposals during July. Cycle 5 observations will start on October 4, 1995. Instrument Reports EGRET EGRET operations were normal this monthly period. Delivery of data to the GRO SSC remains on schedule. Interaction with guests investigators continues at a good level. A paper on the evolution of blazars observed to be emitting high energy gamma rays by J. Chiang, C. Fichtel, C. von Montigny, P. Nolan, and V. Petrosian has been accepted by the Astophysical Journal. Evolution of this class of objects has been established; it is seen to be similar to radio bright, flat spectrum AGN, although the uncertainties are relatively large due to the small statistical sample. The four papers on sections of the sky off the galactic plane have now all been submitted to a journal. The Second EGRET Catalog received a favorable review. The suggested changes are being accomodated and the paper will be resubmitted shortly. We hope that approval will come in the not too distant future. Several papers on new results will be presented at the Third Compton Symposium in June. Following the completion of the Mrk 421 observation on May 9, 1995, the rest of May will be spent examining the Orion region. OSSE OSSE operations are normal. Detector motor drive #1 continues to operate without error. Since 10 April, the slewing response to BATSE burst triggers has been disabled, since the BATSE burst trigger is set to the low energy (25-100 keV) band. Two gamma ray bursts occurred serendipitously within the OSSE field of view in the last month. Burst GRB950421 was clearly detected to several MeV, and was in the fields of view of COMPTEL and EGRET as well. Burst GRB950430 we positioned to +-0.2 deg along the OSSE scan direction. Analysis of both bursts continues. OSSE papers on blazars (McNaron-Brown et al., ApJL) and pulsars (Schroeder et al. ApJ) have recently been accepted, and preprints are available over the WWW at URL http://osse-www.nrl.navy.mil/gamma/osse/preprint/osselib.html. McNaron-Brown et al. report OSSE spectra of five EGRET blazars, four of which show clear evidence for spectral breaks between the hard X-ray and medium energy gamma-ray bands. Schroeder et al. give upper limits on low energy gamma ray emission from a large number of radio pulsars. Recent observations are listed in the following table. View period Dates Target (owner) 419.1 4-11 Apr Orion (Guest Investigator H. Bloemen) MCG-2-58-22 (Guest Investigator R. Petre) 415 11-25 Apr LMC X-3 (PI team) South Galactic Pole Survey (PI team) 418 25 Apr - 9 May NGC 4151 (Guest Investigator N. Gehrels) X Per (PI team) Data from viewing periods 313, 314, 315, and 316 were delivered to the Compton GRO Science Support Center archive in the last month. The targets during these periods were Cen A, CTA 102, the galactic center region, PSR B1259-63, and the Virgo sky survey. COMPTEL The COMPTEL instrument is performing well and continues routine observations. Two cosmic gamma-ray bursts were detected within the field of view of COMPTEL on 21 and 25 April 1995. GRB950421 was detected by BATSE, COMPTEL, EGRET, and Ulysses; the best combined COMPTEL/IPN position for this event is: (RA2000 = 69.35,DEC2000 = -62.22) with a 1-sigma uncertainty of about -/+ 1.5 deg along the IPN annulus. GRB950425 was strongly detected by COMPTEL at MeV energies (approximately 150 events); the best combined COMPTEL/IPN location is: (RA2000 = 164.86, DEC2000 = -33.92) -/+ 1.0 deg (2-sigma) along the IPN annulus. The COMPTEL-determined positions for these events were distributed by the Burst Rapid Response group to those observers who had previously expressed interest; further information can be obtained by contacting either Tom Harrison (tharriso@nmsu.edu), or Marc Kippen (mkippen@comptel.unh.edu). The following papers by the collaboration are currently in press. Most have recently been distributed as preprints, and are also available as postscript documents via anonymous ftp from unhgro.unh.edu (cd to the pub/papers directory). "1.809 MeV gamma-rays from the Vela region" (Diehl et al.); "PKS 0208-512 detected at MeV energies by COMPTEL: A new 'MeV-Blazar' candidate" (Blom et al.); "The black-hole candidate GRO J0422+32: MeV emission measured with COMPTEL" (van Dijk et al.); "COMPTEL upper limits to MeV emission from the globular cluster 47 Tucanae" (O'Flaherty et al.); "The All-Sky Pulsar Search at 0.75-30 MeV by Comptel" (Carraminana et al.); "The detection of an unidentified variable gamma-ray source by COMPTEL" (Williams et al.). All will appear in Astronomy and Astrophysics. The recent ESLAB conference "Toward the Source of Gamma-Ray Bursts," held in Noordwijk, The Netherlands, was attended by about 150 scientists from 5 continents and 24 countries. About 120 papers were presented in both poster and oral form. There are still a limited number of copies of the abstract book available; if you would like a copy please send your name and address to: eslab29@astro.estec.esa.nl. Preparations for the Third Compton Symposium next month in Munich are proceeding on schedule. A preliminary program including contributed presentations has recently been distributed. Attendees should note that conference registration and hotel reservations should have been made by now to obtain the lowest rates. The latest information regarding the Symposium can be found at the following URL on the Web: http://cgro95.mpe-garching.mpg.de/cgro95.html. Finally, the COMPTEL team announces that new WWW pages containing general information on the COMPTEL instrument and the collaboration are now available on the Web. These main COMPTEL WWW pages are accessible from the COSSC home page (at URL http://cossc.gsfc.nasa.gov/cossc/cossc.html), and contain links to the four COMPTEL home institutions at MPE, SRON-Utrecht, UNH, and ESA/ESTEC. BATSE Several BATSE team scientists presented papers at the 29th ESLAB symposium, "Towards the Source of Gamma-Ray Bursts". Michael Briggs reviewed GRB burst global properties, focusing on isotropy and inhomogeneity and their implications. Jon Hakkila discussed limits on burst repetition and the GRB intrinsic luminosity function. Chryssa Kouveliotou reviewed SGR observations. Bonnard Teegarden reviewed BATSE GRB Spectroscopy. David Band discussed searches for absorption lines in GRBs. Rob Preece discussed low- and high-energy spectra of GRBs. A letter to Nature by the BATSE Team and NRAO observers on the x-ray/radio jet transient GRO J1655-40 appeared in the April 20th issue (Nature 374, p. 703-706). This paper describes the relationships between the hard X-ray and radio observations of this source. The following sources have been detected by the BATSE pulsed source monitor since April 1st : Her X-1, Cen X-3, 4U 1626-67, 2S 1417-624, OAO 1657-415, GX 1+4, Vela X-1, 4U 1145-619, and GX 301-2. The outburst of 4U1145-619 is the sixth from this source that has been detected by BATSE. The BATSE burst trigger energy range was set to 25-100 keV beginning on April 12 (TJD 9819). From February 17 (TJD 9765) to April 12 BATSE had been set to trigger on energies > 100 keV. During that interval, there were a total of 69 triggers, of which 36 were gamma-ray bursts, 7 were terrestrial gamma flashes, 1 was a solar flare, and 3 were attributed to Cygnus X-1 fluctuations. As of TJD May 5th BATSE has detected 1278 gamma-ray bursts out of a total of 3437 on-board triggers in 1473 days of operation. There have been 756 triggers due to solar flares with emission above 60 keV, 9 due to SGR events, and 48 due to terrestrial gamma-ray flashes.