Compton Observatory Science Report #183, Tuesday, July 7 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 The observatory was reoriented last week (6/30) to observe the ToO PKS 1622-297, a blazar QSO which was found (by EGRET) to be exceptionally bright in high-energy gamma-rays; PIs J. Mattox (EGRET), W.N Johnson (OSSE). Some additional details are given in the EGRET and OSSE instrument reports below. The ToO observations will continue through monday 7/10. The Cycle-5 Proposal Review process is essentially complete - notification letters are being mailed out for any programs not effected by the timeline. The timeline was constructed last week by the CGRO timeline committee, and it is currently undergoing final constraint checking by at the Goddard Flight Dynamics Facility. All other notification letters will hopefully be mailed out next week. Once all letters are sent, the titles and abstracts of accepted proposals and the Cycle-5 timeline will be posted on GRONEWS and the WWW as well. Thanks for your patience! The CGRO Users Committee will meet at Goddard this month: July 19 and 20, 1995. Topics of discussion will include plans for the next orbit reboost, the use of EGRET after its last gas refill, results of the Cycle-5 proposal review and subsequent NRA releases. Guest Investigator input, via contacting a current member of the User's Committee, is encouraged. A listing of the committee membership and their e-mail addresses and phone numbers is available on GRONEWS grossc.gsfc.nasa.gov (login as GRONEWS) or on the WWW (http://cossc.gsfc.nasa.gov/cossc/cossc.html). Instrument Reports EGRET EGRET operations were normal this monthly period. Delivery of the final phase 3 data to the GRO SSC remains on schedule and delivery of the phase 4 preliminary data to the GRO SSC is now running ahead of schedule. Interaction with guest investigators continues at a good level. During the last month, there have been two objects which have become very bright. Both have been reported in IAU telegrams. One is 1622-297, a radio loud, flat spectrum quasar, which had not been seen previously. The other is GRO J1629-49, whose galactic position is l=335.0, b=-0.4, with a 95% confidence radius in the quicklook data of 0.7 degrees. This uncertainty will be very substantially improved in the final analysis. Although it became one of the brighter sources ever seen, it had not been seen before in high energy gamma rays. Its association with a source seen at other wavelengths is not yet certain, although there is a strong radio source listed in the Parkes-MIT-NRAO catalog, PMNJ 1628-4936, within the present error contour. Inquires on the former source should go to John Mattox and on the latter to Gottfried Kanbach. There was a summary of EGRET results presented at the Third Compton Symposium along with several other papers. Over fifty gamma ray emitting blazars have been seen now, and the number is still growing. An estimate of the evolution of the gamma-ray emitting quasars has been made by Chiang and colleagues. Common characteristics of both blazars and pulsars are emerging. The possible detection of another high energy gamma-ray pulsar was reported by Ramanamurthy and coworkers at this meeting. The general EGRET summary was given by Carl Fichtel, a pulsar summary by Pat Nolan, the galactic diffuse summary by Stan Hunter, and the extragalactic result by Don Kniffen. On July 10, 1995, the pointing direction changes to the Cen-A region, which in addition to this source contains several pulsars and previously detected high energy gamma-ray sources. OSSE OSSE operations are normal. The slewing response to BATSE burst triggers was enabled 30 June, following some changes to BATSE flight software to protect against false triggers. Recent observations are listed in the following table. View period Dates Target (owner) 422 13-20 Jun Gal plane near (355,0) (PI team) MCG-6-30-15 (GI N. Gehrels) 423 20-30 Jun Gal plane near (0,0) (GI J. Tueller) GX 304-1 (GI M. Maisack) 423.5 30 Jun - 10 Jul PKS 1622-297 Vela X-1 Data up to viewing period 323 have been delivered to the Compton GRO Science Support Center archive. The flaring gamma-ray blazar PKS 1622-297 is clearly detected by OSSE in the current Target of Opportunity viewing period. We have submitted the following for inclusion as an IAU Circular: PKS 1622-297 J.D. Kurfess, J. E. Grove, K. McNaron-Brown and W. N. Johnson, Naval Research Laboratory, on behalf of the OSSE team; J. R. Mattox, University of Maryland and Universities Space Research Association; S. Wagner, Landessternwarte Heidelberg; J. R. Webb, Florida International University, communicate: "Optical observations of PKS 1622-297 at Calar Alto, La Silla, and with the SARA telescope on Kitt Peak indicate that it is now at least 17th magnitude - at least 3 magnitudes brighter its historical value. The OSSE instrument aboard COMPTON detects this quasar from 50-200 keV at a significance of 6 sigma during the interval June 30 - July 6, with an indication that the flux is somewhat higher on July 5-6. The EGRET instrument aboard the COMPTON Observatory continues to detect PKS 1622-297. The high energy gamma ray flux peaked on June 25, and has declined since then. The COMPTON observations have been extended until July 10, and the OSSE instrument will continue monitoring the source through July 24. Observations at other wavelengths continue to be very important." COMPTEL The COMPTEL instrument is performing well and continues routine observations. The following two papers by members of the collaboration have recently been distributed as a preprint, and will also soon be available as postscript documents via either anonymous ftp from unhgro.unh.edu (cd to the pub/papers directory), or via the COMPTEL WWW pages accessible from the COSSC home page (see below): "Spectral Characterisation of Gamma-ray Bursts with COMPTEL and BATSE" (Hanlon et al.); "Search for a Radio Counterpart to GRB 940301 with Westerbork" (Hanlon et al.), both from the recent ESLAB Symposium "Toward the Source of Gamma-ray Bursts" (Astophysics and Space Science, in press). The article by Blom et al. on "PKS 0208-512 detected at MeV energies by COMPTEL: a new `MeV-Blazar' candidate" has just appeared in Astronomy and Astrophysics, volume 298, page L33. The 3rd Compton Symposium recently held in Munich was considered a great success by all who attended. The organizers remind all attendees that contributions to the proceedings volume are due by September 1. Among the many results presented at the symposium by members of the collaboration was the first report on COMPTEL measurements relating to the extragalactic cosmic diffuse radiation at MeV energies; the preliminary results presented by Kappadath et al. indicate that the "MeV bump" reported by earlier experiments may in fact be much less pronounced than previously believed. A new version of the COMPTEL pages on the World Wide Web will soon be available; these will be accessible via the COMPTEL home page maintained by the COSSC (at URL http://cossc.gsfc.nasa.gov/cossc/COMPTEL.html). Among other enhancements, these new pages include improved links to the various COMPTEL sites, as well as to the personal home pages of COMPTEL team members. After the excitement of the recent Compton Symposium all attention within the team is currently focused on the 82nd Tour de France, now underway. After some initial controversy regarding the entry of the Telekom team from Germany, the question on everyone's lips is: Will Miguel "The Train" Indurain of Banesto become the first to win five consecutive Tours? As a service to the high-energy community, the latest Tour results and updates are now accessible in near-real time via the main COMPTEL pages on the WWW (see above). BATSE Hard X-ray emission continues to be detectable from the sources GX 339-4 and GRS 1716-249 = GRO J1719-24 at about the 100-150 mCrab level in the 20-100 keV band. The outburst from GX 339-4 has lasted about two months and is less intense than previous outbursts in 1991-1994. The initial outburst of GRO J1719-24, an x-ray nova in Ophiuchus, was in September-October of 1993. The following sources have been detected by the BATSE pulsed source monitor in the last month : Her X-1, Cen X-3, 4U 1626-67, 2S 1417-624, OAO 1657-415, GX 1+4, Vela X-1, and GX 301-2. The paper, "The nu F_nu Peak Energy Distribution of Gamma-ray Bursts Observed by BATSE" by R.S. Mallozzi, W.S. Paciesas, G.N. Pendleton, M.S. Briggs, R.D. Preece, C.A. Meegan, and G.J. Fishman has been accepted for publication in the Dec 1 issue of Astrophysical Journal. The BATSE burst trigger continues to operated on the 25-100 keV energy range. As of July 2 BATSE has detected 1311 gamma-ray bursts out of a total of 3556 on-board triggers in 1531 days of operation. There have been 757 triggers due to solar flares, 9 due to SGR events, and 48 due to terrestrial gamma-ray flashes.