Compton Observatory Science Report #186, Friday, October 6, 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 Cycle 5 is here! Observations began this week. Several recent updates to the CGRO Cycle-4 and -5 timelines have been made recently, due to both the occurrence of the GRO J2058+42 target of opportunity (see the BATSE and OSSE reports below), and due to a computational error in the original Cycle-5 timeline generation. The corrected versions have been distributed by electronic and normal mail to all current Guest Investigators. As a consequence of Goddard's efforts to streamline its management structure, the SSC has a new mail code: future correspondences should to the SSC should use mail code 660.1 instead of 668.1. Otherwise, we're all still here in the same place! 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 also on schedule. Interaction with guest investigators continues at a good level. All of the relevant information for phase 5 is in the computors, and we are ready to handle the cycle 5 data . All cycle 5 guest investigators who have expressed an interest in working with a member of the EGRET team should have received a letter from Carl Fichtel by now giving relevant information; if anyone has not, please contact Carl Fichtel by e-mail. fichtel@lheavx.gsfc.nasa.gov. Papers on high energy gamma rays from bursts will be presented at the Huntsville Burst Meeting, along with a report on the search for microsecond bursts predicted by the Hawking unification theory. A very extensive improved normalization for the EGRET data that has utilized all of the data and involved several cross-checks is nearing completion after a long period of intense work. It will include not only an improved normalization above 100 MeV, but normalizations for each energy interval for each viewing period. We expect this work including the tests and checks to be completed in six to eight weeks, at which time it will be transferred to the Compton Gamma Ray Observatory Science Support Center in final form for use by everyone. Cycle 5 began on October 3 with a pointing centered on galactic coordinates (l = 28.0, b = 3.6). As with the great majority of the cycle 5 pointings, EGRET will be in the narrow field mode. OSSE At the start of Cycle 5, after more than four years on orbit, OSSE is working as designed, with all subsystems in complete and full operation. The slewing response to BATSE burst triggers has been enabled since 30 June. Recent observations are listed in the following table. View period Dates Target (owner) 427 22 Aug - 7 Sep MCG +8-11-11 (PI team) NGC 3227 (GI R. Cameron) 428 7-20 Sep NGC 253 (GI D. Bhattacharya) Vela region (GI R. Diehl) 429 20-27 Sep AE Aqr (GI J. Bookbinder) Sco X-1 (PI team) 429.5 27 Sep - 3 Oct GRO J2058+42 (PI team) NGC 5548 (not assigned) 501 3-17 Oct QSO 1741-038 (PI team) 3C 279 (PI team) AE Aqr (GI J. Bookbinder) Viewing period 429.5 was a Target of Opportunity pointing designed to help locate the X-ray pulsar GRO J2058+42 recently discovered by BATSE. Data from the first few days were used to generate the error box given in the IAU circular below, and the remaining days were used for spectroscopy. OSSE clearly detects pulsations at the ~198-sec spin period of the neutron star. The phase-averaged spectrum above 50 keV is consistent with a 10 keV exponential cutoff. GRO J2058+42 J. E. Grove, Naval Research Laboratory, reports on behalf of the Compton Gamma Ray Observatory (CGRO) OSSE team: "We have further constrained the position for GRO J2058+42 using the OSSE instrument on the CGRO. Data from a 1-dimensional scan through the source region were combined with the published BATSE error box (IAUC 6238) to yield a new 95-percent confidence region of size about 30' x 60', bounded by a quadrilateral with the following vertices (equinox 2000.0): R.A. = 21h00m.5, Decl. = +41o42'; 20h59m.5, +42o12'; 20h57m.5, +41o21'; 20h58m.3, +40o51'. Follow-up observations in other wavebands to identify the object are encouraged." Data up to viewing period 332 have been delivered to the Compton GRO Science Support Center archive. OSSE team members have recently submitted a number of papers to be published in the proceedings of the 1995 Compton Symposium, covering a broad range of topics: Galactic compact objects: (GRO J1655-40 [Kroeger et al.], Cyg X-1 [Phlips et al.], Cyg X-3 [Matz et al.], GS 1826-34 [Strickman et al.]); Supernova remnants: (Cas A [The et al.], Vela SNR [Strickman et al.]); Diffuse galactic emission (lines [Harris et al.], continuum [Purcell et al.], positronium [Kinzer et al.], electrons in the ISM [Skibo et al.]); Extragalactic objects: (blazars [McNaron-Brown et al.]); and an overview by Kurfess. After the papers are reviewed, they will appear with other OSSE preprints under the OSSE home page on the WWW at URL http://osse-www.nrl.navy.mil/. COMPTEL The COMPTEL instrument is performing well and continues routine observations, now in CGRO Cycle 5. Preprints are currently being prepared for distribution containing collaboration papers presented at the recent International Cosmic Ray Conference in Rome, and the 3rd Compton Symposium in Munich. A delivery to the COSSC public archive of low-level and first high-level data products for Viewing Periods 308 to 323 has just recently been completed. This delivery also includes an update to several Phase 1 datasets which have undergone improved processing since their initial delivery. There will be a general team meeting of the collaboration next week (Oct 10-13) at the University of New Hampshire. Preparations are nearly complete for the official celebrations marking the beginning of the CGRO Cycle 5 observing season AND the arrival of TJD 10000 (and the wagers have already been placed to see which computer programs will hang due to the extra digit in the TJD field). Our Dutch colleagues inform us that, in honor of the new millenium in TJD, all phone numbers in Holland will change on that date (October 10). BATSE The following notice appeared in IAU Circular 6238: GRO J2058+42 C. A. Wilson, S. N. Zhang, M. H. Finger, R. B. Wilson, and M. Scott, Marshall Space Flight Center, NASA; and T. Koh, D. Chakrabarty, B. Vaughan, and T. A. Prince, California Institute of Technology, report for the Compton Observatory BATSE team: "Pulsations from a previously-uncatalogued source in the Cygnus region in the energy band 20-50 keV have been detected since Sept. 14 and continue to be detected through Sept. 25. A preliminary location (95-percent confidence) is bounded by a quadrilateral with vertices (equinox 2000.0) at R.A. = 21h03m, Decl. = +40o.2; 20h56m, +44o.0; 20h53m, +43o.2; 21h01m, +39o.4. Positions estimated independently from the pulsed and total flux are consistent. An rms pulsed flux of 130 +/- 40 mCrab in the energy band 20-50 keV was observed on Sept. 23. Observations between Sept. 20 and 23 show pulsations up to at least 70 keV and are consistent with a barycentric pulse frequency of 5.05618(7) x 10E-3 Hz on Sept. 22.0 UT with a frequency derivative of 1.70(7) x 10E-11 Hz/s. The total flux, measured by Earth occultation, increased from < 100 mCrab on Sept. 17 to 280 +/- 50 mCrab on Sept. 22 in the band 20-100 keV and has remained approximately constant (within 15 percent) from Sept. 22 to 24. The energy spectrum of the total flux on Sept. 20- 24 was well fit by an optically-thin thermal bremsstrahlung model with kT = 17 +/- 1 keV from 20 to 100 keV." The following notice appeared in IAU Circular 6242: SGR 1806-20 C. Kouveliotou, G. J. Fishman, C. A. Meegan, and K. Hagedon report for the Compton Observatory BATSE Team: "We have detected transient soft-gamma-ray emission from a region consistent with the direction of the 'soft gamma repeater' (SGR) 1806-20. The BATSE location is centered at R.A. = 272 deg, Decl. = -20 deg and has an error radius of about 4 deg. The outburst was recorded on Sept. 30.72852 UT and consists of one pulse with a triangular shape and 60-ms duration (40 ms FWHM). The spectrum of the event has an upper energy cutoff of about 100 keV, consistent with a typical SGR spectrum. Follow-up observations of the source region at other wavelengths are strongly encouraged. " The BATSE pulsed source monitor has detected the following sources in the last month : Her X-1, Cen X-3, GRO J1750-27, 4U 1626-67, OAO 1657-415, GX 1+4, GRO J2058+42, Vela X-1, 4U 1145-619, and GX 301-2. The outburst from GRO J2058+42 is still being detected. GRS 1915+105 was in outburst (100-200 mCrab in the 20-100 keV band) from approximately September 25 to October 4. The BATSE burst trigger is using discriminator channels 1+2 (~20-100 keV) to enhance sensitivity to SGR events. As of October 5 BATSE has detected 1375 gamma-ray bursts out of a total of 3745 on-board triggers in 1626 days of operation. There have been 758 triggers due to solar flares, 10 due to SGR events, and 49 due to terrestrial gamma-ray flashes. The BATSE WWW page (http://xanth.msfc.nasa.gov/astro/batse/batse_home.shtml) now contains the program and the abstracts for the upcoming Huntsville Burst Workshop. Several recent papers by BATSE team members are also available.