Compton Gamma Ray Observatory Status Report #194 Monday, July 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: The CGRO Cycle-6 proposal review was held late last month. The broad consensus is that there is still an abundance of top quality science forthcoming! No final results will be announced until after the timeline committee meeting which occurs later this month. Shortly thereafter, letters of acceptance/rejection and, where appropriate, budget solicitations will be sent via e-mail. A proposal, prepared by the CGRO Users Committee, was submitted to the NASA HQ MO&DA Senior Review for evaluation later this month. The outcome of this review will determine the level of support for the project during FY 98 and beyond. High-level data products (BATSE, OSSE and COMPTEL)from the recent Cyg X-1 ToO will be available imminently on the CGRO SSC WWW site (http://cossc.gsfc.nasa.gov). These include PostScript plots, ascii and FITS formatted data files and "PHA" spectral-data files for use with the HEASARC "XSPEC" software. Instrument Team Reports: EGRET The high voltage for the track imaging system of EGRET has been off since June 14, 1996 to conserve the remaining gas, since the astrophysical objects in the field of view were judged by the proposal review committee to be of lesser priority. It will be activated on either July 23 or July 30, 1996 depending on whether or not a target of opportunity is declared. Delivery of the final phase 4 data to the GRO SSC is 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. EGRET papers that have appeared in the Astrophysical Journal recently include: "EGRET Observations of the North Galactic Pole Region", by Sreekumar et al. (June 20), "Possible EGRET Gamma-Ray Burst Detection Independent of BATSE Triggering", by Jones et al. (June 1), and "EGRET Observations of High- Energy Gamma Radiation from PSR B1706-44", by Thompson et al. (July 1). At the June American Astronomical Society Meeting, Carl Fichtel et al. showed that, within the limits of the statistics available, the distribution in z of the high energy gamma-ray emitting flat-spectrum radio-loud blazars was the same as all flat-spectrum radio-loud blazars, and a similar statement could be made for the gamma-ray emitting BL Lac objects and all radio emitting BL Lacs. Hence, the gamma-ray emitting BL Lacs are closer and less luminous on the average. No statistically significant difference was found in the energy spectral slopes of the high-energy gamma-ray emission from these two types of blazars. OSSE OSSE operations are normal. The instrument is working as designed, with all subsystems in complete and full operation. The slewing response to BATSE burst triggers was enabled on day 96/135. Since this time there have been no burst triggers sent from BATSE that have met the OSSE slewing criteria. The OSSE Orion complex paper has been accepted for publication in ApJ (Murphy et al.). Preprints are available on the OSSE preprint WWW page at URL http://osse-www.nrl.navy.mil/osselib.htm. Flux levels reported by COMPTEL of gamma-ray line emission in the 3-7 MeV range suggest that if the origin of the emission were a point source at the center of the OSSE field of view then OSSE observations of the region would result in significant detections of line emission near 4.4 and 6.1 MeV. The lack of compelling evidence for an OSSE detection in this region requires that any source of this emission must be more extended than the distribution of the intense CO emission localized around Orion A and Orion B. OSSE strongly detected Cyg X-1 in its gamma-ray low state in the recent target of opportunity observation (VP 522.5). The Rossi XTE observed Cyg X-1 during the same interval, providing an unprecedented opportunity to obtain a broadband spectrum in this state. While coordinated spectral analysis has not yet been performed on these data sets, we expect to establish that the gamma-ray low state, with its moderately steep power law spectrum, is associated with the X-ray high (soft) state. In VP 522.5, OSSE detects emission up to about 800 keV. The spectrum is consistent with a single power law with photon index = -2.5, with some evidence that the spectrum is beginning to turn over with an exponential folding energy of >600 keV. Recent observations are listed in the following table. View period Dates Target (owner) 522 11-14 June Cen X-3 (T. Vestrand) Orion GMC (M. Harris) 522.5 14-25 June Cyg X-1 (public) V 0332+53 (public) Crab Pulsar (public) 523 25 June - 9 July Orion GMC (M. Harris) Mrk 421 (public) NGC 4151 (A. Zdziarski) 524 9-23 July GX 339-4 (E. Liang) Vela Pulsar (A. Harding) Low-level OSSE data products through viewing period 419.1 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. All products for the VP 522.5 Cyg TOO will be delivered within the week. 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. Due to a small processing problem discovered in the VP 522.5 Cygnus X-1 data set, it is being reprocessed and is expected to be re-delivered to the SSC by 7/17/96. COMPTEL The COMPTEL instrument is performing well and continues routine operations. The collaboration has carried out an accelerated processing of the data associated with the recent target-of-opportunity observation of Cyg X-1 (VP 522.5). Preliminary analysis indicates elevated flux levels from this source, when compared to earlier epochs. Further details on these first results, along with related data products, will be made publicly available shortly via the COMPTEL pages on the WWW. The drought of non-detections of gamma-ray bursts occurring within the field of view of COMPTEL continues: neither GRB 960705 nor GRB 960702 was detected at MeV energies by the instrument. The organizers of the upcoming INTEGRAL workshop in St. Malo, France announce that the scientific programme, including abstracts and schedule information, is now available on the WWW via the INTEGRAL home page at: http://astro.estec.esa.nl/SA-general/Projects/Integral/integral.html The third and final circular for the INTEGRAL workshop, with information on travel, list of participants, paper-preparation kit, etc, is available on these WWW pages, and will also be mailed to all registered participants in early July. Lastly, the 83rd Tour de France is well underway (in snow!). Will Indurain become the first to achieve an unprecedented sixth consecutive victory?! BATSE The following report was submitted to the IAU Circulars: 2S 1417-624 M. H. Finger and M. Scott, Universities Space Research Association, T. A. Prince and B. Vaughan, Caltech, and R. B. Wilson, NASA/Marshall Space Flight Center, report for the BATSE/Compton Observatory team: "Renewed activity from the X-ray transient pulsar 2S1417-624 is being observed. Hard X-ray pulses were first detected on June 30, with the pulsed flux rising to 17 +- 3 mCrab (20-50 keV) by July 8. A barycentric frequency of 0.05694816(25) Hz on July 4.5 and barycentric frequency rate of 3.35(14)x10E-11 Hz/s were obtained from a fit of frequency measurements from July 1-8. The source had been undetected by BATSE since a series of six outbursts were observed, beginning on August 26 1994 (IAUC 6075) and ending July 8 1995." 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, 2S1417-624, EXO 2030+375, OAO 1657-415, Vela X-1, and GX 301-2. The current outburst of EXO 2030+375 is the third in a consecutive series of outbursts occurring near periastron passage. Earth occultation monitoring over the past month has shown considerable activity from transient sources. GRO J1655-40 has been bright (~0.6-0.8 Crab 20-100 keV), in recent days; also GRS 1915+105, GX 339-4 and 4U 1630-47 have been detected. Cyg X-1 remains in a very low hard X-ray/gamma ray state, dropping to 100-150 mCrab in the 20-100 keV band. Another 150 days of Earth occultation data (TJD 9200-9350, Aug 1-Dec 29, 1993) for 25 hard X-ray sources (list available at the COSSC) have been delivered to the public database. The burst trigger is currently using count rates from above 100 keV. As of July 9 BATSE has detected 1593 gamma-ray bursts out of a total of 5429 on-board triggers in 1904 days of operation. There have been 767 triggers due to solar flares, 10 due to SGR events, 55 due to terrestrial gamma-ray flashes, and 1477 due to the bursting pulsar GRO J1744-28.