Compton Observatory Science Report #180, Friday March 31, 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 proposal deadline is now only a week away!!! If you have not done so already, please take a moment and read the short bulleted list of changes to the NRA and proposal submission precess at the beginning of Appendix A. The most significant things to note are that the EGRET instrument will typically be configured in alternate gas-saving modes for Cycle-5 and beyond -- If your using EGRET please section IV-I of appendix G (or at least look at figure IV-3). Electronic submission of proposal forms is now required (send a blank e-mail message to rps@cossc.gsfc.nasa.gov for instructions - if you have questions send us e-mail. We are additionally requiring two-sided copy and have imposed page limits on the (optional) vitae materials appended to proposals. The CGRO public data archive available intermittently over the next several days, as technical problems with our optical Juke Box persist. Please be patient -- we realize that this is a rather inopportune time for this to occur and we apologize for the inconvenience. Tom Bridgman has joined the CGRO-SSC our new OSSE Instrument Scientist. Feel free to contact him with any OSSE related proposal preparation or data analysis questions (bridgman@grossc.gsfc.nasa.gov). Instrument Reports EGRET The EGRET spark chamber high voltage pulsars were turned off beginning on March 21, 1995 as planned to conserve the spark chamber gas since the field of view was not of high priority for EGRET observations. It will be turned on again on April 4, 1995, and normal operations will resume at that time. Delivery of data to the GRO SSC remains on schedule. Interaction with guest investigators continues at a good level. OSSE OSSE operations are normal. Detector motor drive #1 continues to operate without error. The slewing response to BATSE burst triggers is enabled. In viewing period 414 (21-29 Mar), the Z-axis target was LMC X-1 (PI team) and the X-axis target was the South Galactic Pole Survey (PI team). When both targets were occulted by the Earth, the target was the galactic plane (PI team) near (l,b) = (280,0). In Target of Opportunity viewing period 414.3 (29 Mar - 4 Apr), the Z-axis target is the X-ray nova GRO J1655-40 in outburst (PI team), and the X-axis targets are CTA 102 and QSO 2251+158 (PI team). Spectra of the X-ray nova from the first few hours of observation have been analyzed and give a lower limit on a thermal cutoff of ~400 keV. Data from viewing periods 311.0, 311.3, 311.6, and 312 were delivered to the Compton GRO Science Support Center archive these last two weeks. The targets during these periods were the Virgo region sky survey, PSR 1800-21, and the galactic plane near (l,b) = (343,0). COMPTEL The COMPTEL instrument is performing well and continues routine observations. A cosmic gamma-ray burst was observed within the field of view of COMPTEL on 17 March 1995. Unfortunately, as with other recent events, though the BATSE/BACODINE intensity threshold was exceeded for an automated rapid-response analysis by the COMPTEL burst group, no emission from this event was observed at MeV energies. As elsewhere in the high-energy community, the collaboration is extremely preoccupied at present with the preparation of proposals (due 7 April) for CGRO Cycle 5 observations, and abstracts (due 31 March) for the upcoming Third Compton Symposium in Munich in June. There will be a general team meeting of the COMPTEL collaboration next week at ESA/ESTEC in The Netherlands to discuss these and other matters. BATSE The following was included in IAU Circular No. 6152: X-RAY NOVA 1994 IN SCORPIUS C. A. Wilson, B. A. Harmon, S. N. Zhang, W. S. Paciesas, and G. J. Fishman report for the Compton Observatory BATSE Team: "The x-ray/radio transient GRO J1655-40 is undergoing a major outburst in hard x-rays above 20 keV. Preliminary fluxes for the past several days in the band 20-100 keV are: Mar. 17, 240 +/- 20 mCrab; 18, 470 +/- 30; 19, 500 +/- 30; 20, 480 +/- 40; 21, 1200 +/- 50. The source has been detectable since mid-February (IAUC 6147), but generally at lower intensity (50-300 mCrab). The spectrum extends to at least 200 keV and is well fit by a power law with spectral index varying between -2.5 and -3.1. The spectrum tends to soften as the intensity increases." The following was included in IAU Circular No. 6153: GX 1+4 D. Chakrabarty, T. Koh, T. A. Prince, and B. Vaughan, California Institute of Technology; M. H. Finger and M. Scott, Universities Space Research Association; and R. B. Wilson, Marshall Space Flight Center, NASA, report for the Compton Gamma Ray Observatory BATSE team: "The accreting x-ray pulsar GX 1+4 has undergone another torque reversal, and resumed spinning down on around Mar. 2, thereby ending an extended spin-up episode that began on 1994 Oct. 30 (IAUC 6105). On Mar. 17.0 UT, the barycentric pulse frequency was (8.21119 +/- 0.00002) x 10E-3 sE-1, with a mean frequency derivative of (-1.25 +/- 0.04) x 10E-12 sE-2. The phase-averaged pulsed intensity on this date was (9.0 +/- 0.9) x 10E-4 photon cmE-2 sE-1 keVE-1 at 30 keV, with a power-law photon index of 2.6 +/- 0.2 for the 20- to 100-keV pulsed flux." The following sources were detected by the BATSE pulsed source monitor in the past two weeks: 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. As of March 28 BATSE has detected 1255 gamma-ray bursts out of a total of 3382 on-board triggers in 1435 days of operation. There have been 749 triggers due to solar flares with emission above 60 keV. The BATSE team World Wide Web page is accessible to the world at the following URL: http://xanth.msfc.nasa.gov/astro/batse/batse_home.shtml >From this page the reader can find a description of the instrument, a list of sources observed by BATSE, some descriptions of results from BATSE, some abstracts from some recent BATSE papers, PostScript files of some BATSE preprints, and upcoming conferences related to sources observed by BATSE, including the home page for the Third Huntsville Gamma-Ray Burst Symposium. We intend to make all preprints from the group available through this page. Many pages are under development and will be added to the home page when complete. Suggestions for improvement (to the author of the pages) are welcome.