Compton Gamma Ray Observatory Status Report #200 Friday, January 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 issued in about mid February, which is abou one month later than in our original plans. The proposal due date will be in mid-May. One fortuitous consequence of this delay (we won't mention non-fortuitous ones) is that the 4th Compton Symposium will proceed the proposal submission deadline. Cycle-7 will start on time, on November 12, 1997 - thus, dissemination of the latest results from the mission will final precede proposal preparation. If you have not received the second announcement for the 4th Compton Symposium, pleas refer to the WWW site: http://osse-www.nrl.navy.mil/cgrosymp.htm. The Symposium will take place on April 27-30, 1997, in Williamsburg Virginia. EGRET EGRET operations were normal this monthly period. Delivery of the final phase 5 data to the GRO SSC is beginning and is on schedule, and delivery of the phase 6 preliminary data to the GRO SSC is also beginning and is on schedule. Interaction with guest investigators continues at a good level. A major paper author summarizing the results of EGRET observations of AGN with Reshmi Mukherjee as the lead has been submitted to the Astrophysical Journal. This paper gives the intensities, spectra, and time histories of these AGNs, along with information on the average spectrum and a study of the luminosity as a function of z. As soon as it is accepted, preprints will be made available. At the present time, EGRET continues its observation of 3C 279. COMPTEL The COMPTEL instrument is performing well and continues routine observations into the New Year. The gamma-ray burst GRB 961212 was detected within the field of view of COMPTEL in mid-December. Automated rapid processing was carried out for this event and location information disseminated electronically to interested observers for rapid followup in other wavebands. Further details on this event will soon be available on the Gamma-Ray Burst page at the collaboration's COMPTEL WWW site. Information on the general status of gamma-ray burst studies with COMPTEL will also be available at the upcoming 189th meeting of the AAS in Toronto, in a presentation by Connors et al. Also at the AAS meeting will be reports on solar results obtained with the COMPTEL instrument (by Rank et al, and Young et al), and on a first all-sky search for 2.2-MeV line emission from astrophysical sources (by McConnell et al). The Proceedings of the Third Compton Symposium (Munich) have just appeared in the Astronomy & Astrophysics Supplement Series, Vol 120, No. 4 (December III, 1996). 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 disabled to protect against slews to the bursting pulsar GRO J1744-28, which is once again active and near the scan plane. Bursts, flares, transients, and SGRs through 3 Jan 1997 have been processed. In the last month, 21 classical GRB triggers occurred, of which 11 produced significant responses in the shields. None produced significant responses in the central detectors. None of the 7 triggers from SGR1806-20 produced an obvious signal in the shields or central detectors. Slewing was enabled from 6 Dec 1996 to 6 Jan 1997, during which time there were 4 triggered slews, 2 from SAA passages, 1 from an SGR event, and 1 for a strong GRB (#5725 on 961225). The slew to the GRB put OSSE on the BATSE position within 25 sec. BATSE gave a duration of 50 s for this event, so we may well detect the tail of this Christmas burst. Analysis is in progress. The new bursts are available on the WWW at . "Long Term Monitoring of NGC 4151 by OSSE" by W.N. Johnson et al. has been accepted for publication and will appear in the 10 June issue of ApJ. It reports the strongest limits to date on nonthermal emission processes and pair production in a Seyfert AGN. Submissions to the proceedings of the Second Integral Workshop have also been accepted, including "Gamma Ray Line Obervations with OSSE" by J.D. Kurfess et al. and "Two Gamma Ray Spectral Classes of Galactic Black Hole Candidates" by J.E. Grove et al. M.J. Harris et al. have submitted to A&A an updated analysis of all OSSE spectra of the Orion molecular cloud complex obtained through the end of 1996. They find no evidence for line emission in the 3-7 MeV range, and exclude the possibility that the COMPTEL emission arises from a single point source with 95% confidence. The OSSE upper limits are consistent with a spatially extended source at the COMPTEL intensity. Recent observations are listed in the following table. We are now completing 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, and a short galactic plane survey will begin soon. A Target of Opportunity will likely be declared beginning 14 Jan to study GRO J1744-28 in its new outburst. View period Dates Target (owner) 604.1 3-10 Dec GAL 003.7-06.5 (W.R. Purcell) Mrk 231 (public) Arp 220 (public) 606 10-17 Dec 3C 279 (W.N. Johnson) GAL 349.1-06.2 (W.R. Purcell) 607 17-23 Dec 3C 279 (W.N. Johnson) GAL 353.5-03.7 (W.R. Purcell) 608 23-30 Dec 3C 279 (W.N. Johnson) GAL 006.5+03.7 (W.R. Purcell) 609 30 Dec - 7 Jan 3C 279 (W.N. Johnson) GAL 010.9+06.2 (W.R. Purcell) Low-level OSSE data products through viewing period 429.5, the final viewing period of Cycle 4, 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 reports of BATSE observations appeared in IAU circulars: Circular No. 6519 XTE J1856+053 AND GRO J1849-03 D. Barret, J. E. Grindlay and P. F. Bloser, Harvard-Smithsonian Center for Astrophysics (CfA); and B. A. Harmon, S. N. Zhang, C. A. Wilson, C. R. Robinson and W. S. Paciesas, NASA Marshall Space Flight Center, report for the BATSE Team: "As part of the galactic-plane survey for faint x-ray transients (Grindlay et al. 1996, A.Ap. Suppl., in press), the CfA BATSE Image Search (CBIS) system for automated analysis of earth-occultation images (Barret et al. 1996, in preparation) was used to scan sky images of the Aql-Sct-Ser region. In a 20-50-keV image integrated over Sept. 3-17 we found evidence of emission from the recently-discovered x-ray transient XTE J1856+053 (IAUC 6504). Also, in images made for the Sept. 3-17 and 16-30 time periods, CBIS reported weak emission from the recurrent transient GRO J1849-03, consistent with the 241-day period reported by Zhang et al. (IAUC 6150). Analysis of the lightcurves for XTE J1856+053 and GRO J1849-03 shows peak fluxes in the 20-100-keV band between 30 and 60 mCrab, with XTE J1856+053 peaking in BATSE data on Sept. 7-9, preceding the ASM peak flux by about 8 days. This behavior is characteristic of low-mass-binary transients and could indicate the presence of a black hole. GRO J1849-03 has a very broad peak around Sept. 19." Circular No. 6525 GRS 1915+105 C. R. Robinson, B. A. Harmon, W. S. Paciesas, K. J. Deal, S. N. Zhang, M. L. McCollough, and C. A. Wilson, for the Compton Observatory BATSE Team; E. B. Waltman, Naval Research Laboratory; and E. Morgan, Massachusetts Institute of Technology, report: "The galactic superluminal jet source GRS 1915+105 has reached the highest flux levels detected in prior outbursts from BATSE, for data averaged over one day. Previously, three strong outbursts were observed, with peaks averaging around 350 mCrab (20-100 keV) and characterized by a power law with photon index between -3.0 and -2.5. This latest hard x-ray outburst has lasted 8 months, rising slower to its peak flux than the other outbursts and exhibiting, until recently, a spectrum steeper than -3.0. Starting around Nov. 24, the source has remained above 350 mCrab, reaching at times 500 mCrab. The spectrum is now harder, with an index of -2.82 +/- 0.04. During this same interval, the RXTE/ASM data (2-10 keV) show average countrates and variability at around their lowest levels thus far detected from this source. Public-domain data from the NSF-NRAO-NASA Green Bank Interferometer, however, reveal the source to be flaring during this interval of high, hard x-ray flux. The largest flare was detected on Dec. 6 at a flux level of nearly 150 mJy (2.25 GHz). Additional observations of this source are encouraged." Circular No. 6530 GRO J1744-28 C. Kouveliotou, Universities Space Research Association (USRA) and Marshall Space Flight Center (MSFC), NASA; K. J. Deal, G. A. Richardson, and M. S. Briggs, University of Alabama in Huntsville (UAH); G. J. Fishman, MSFC; J. van Paradijs, University of Amsterdam and UAH, report: "We have recorded a series of outbursts starting on 1996 Dec. 2 that are consistent with the position of GRO J1744-28, the bursting pulsar. The bursts are detected between 20 and 100 keV, and on Dec. 2 they came in variable rates ranging from every 300 to every 500 s, with a preliminary total number estimated between 80 and 100 events. After Dec. 3, the burst rate dropped to 15-20 bursts/day, where it has remained. The current average error radius of the burst locations is about 4 deg. The burst fluence is currently about 2 x 10E-7 erg cmE-2. This indicates that the source is in outburst again. Although the source location is currently very close to the sun, we encourage observations in other wavelengths whenever possible." M. H. Finger and C. R. Robinson, USRA; B. A. Harmon, MSFC; and B. A. Vaughan, California Institute of Technology, report for the Compton Observatory BATSE team: "Persistent, hard x-ray emission from GRO J1744-28 (IAUC 6272, 6284, 6285) is currently being detected through both pulsation and earth occultation. Pulsations with a period near 0.467 s became detectable on Dec. 17, rising to a 20- to 40-keV-rms-pulsed flux of 1.3(1) x 10E-9 erg cmE-1 sE-1 (170 mCrab) by 1997 Jan. 3. On Jan. 1.0, the intrinsic pulse frequency was 2.1408983(4) Hz, and the spin-up rate was 2.8(5) x 10E-12 Hz sE-1. This assumes the following circular orbit parameters: P = 11.83665(14) days; epoch of longitude 90 deg = JD 2450126.9977(4) TDB; a sin i = 2.6371(5) light-s (determined using data from the 1995 Dec.-1996 Apr. outburst). Earth-occultation monitoring of flux from GRO J1744-28 shows its intensity increasing by a factor of about two during 1996 Dec. 25-1997 Jan. 6. Although source confusion prevents a precise flux estimate, subtracting a 25-percent background for unresolved galactic-center sources yields a persistent flux for Jan. 3-6 in the energy bands 20-30, 30-40, and 40-50 keV of 590, 470, and 290 mCrab, respectively." 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, GRO J1008-57, GX 1+4, 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 28 BATSE has detected 1720 gamma-ray bursts out of a total of 5645 on-board triggers in 2086 days of operation. There have been 778 triggers due to solar flares, 37 due to SGR events, 64 due to terrestrial gamma-ray flashes, and 1477 due to the bursting pulsar GRO J1744-28.