Compton Observatory Science Report #154 Friday, April 1, 1994 Chris Shrader, Compton Observatory Science Support Center Questions or comments can be sent to the Compton SSC. Phone: 301/286-8434 e-mail: NSI_DECnet: GROSSC::SHRADER Internet: shrader@grossc.gsfc.nasa.gov Spacecraft Status The Observatory, scientific instruments and all spacecraft subsystems continue to performing normally. Based on the number of packets of data delivered to instrument teams, the percentage of full time coverage achieved with 32Kbps realtime data between March 16 and March 22 was 80%, including 17% from the GRO Remote Terminal System (GRTS). An additional 5% coverage was achieved with the BATSE 1Kbps data during this time. Engineering tests of the GRTS are continuing. Science Support Center News Proposals are us! As you frantically write and we prepare for the onslaught, please feel free to contact us with any questions regarding the NRA, proposal submission, policy or technical issues. There is an error with the figure V-5 of Appendix G to the NRA - see the BATSE Instrument report for details. Some problems have been found with the target-entry portion of the Unix versions of the proposal form generation software. This effects the Sun and DEC UNIX versions only but NOT THE VERSION ON GRONEWS. For now, we recommend using the GRONEWS version or downloading only the VMS version to use on your VAX. Unix fixes are forthcoming. As noted in the last bi-weekly report, there are several items of potential interst on GRONEWS - lists of previously awarded targets (phase 2 & 3) and carry-over targets (phase3-->4) are available under item 2 (it may be good to see what's been done!). Instrument Reports OSSE OSSE operations are normal. In viewing period 323 (22 Mar - 5 Apr), the Z-axis target is the ADC source H1822-37.1 (Guest Investigator E. Liang), and the X-axis targets are the blazars QSO 2251+158 and CTA 102, along with the recent unidentified EGRET source GRO J2239+12 (Key project). The Sun was not available for slewing on the OSSE scan plane. We have made 700+ high time resolution gamma-ray burst time histories from OSSE available on the Internet via Mosaic. They are current through the end of February, 1994. The appropriate URL is: http://www.astro.nwu.edu/astro/osse/bursts/index.html The data are the total count rates from the four annular NaI shields, typically sampled at 16-ms intervals and covering about 64 sec, 4 s before the burst and 60 s after. They are dumped in response to an on-board trigger provided by BATSE, and we have relied on the BATSE identification to eliminate the solar and terrestrial events. Plots of the events may be browsed and the data from individual events may be downloaded for further study. Please note that the data are raw and in some cases contain artifacts (especially single channel spikes) that are not associated with the bursts. Consult the Mosaic pages for further information. Those who would like access to the data but do not have Mosaic should contact the OSSE team. Data from the following viewing periods have been sent to the Compton GRO Science Support Center archive in the last two weeks. period targets 39 GRO J0422+32, MCG+5-23-16, 3C279 201 Her X-1, Gal plane near (l,b) = (355,0) Delivery of the activation period and Phase 1 is now complete. Viewing periods 201, 204, and 205 from Phase 2 have also been delivered. EGRET EGRET operations were normal this biweekly period. The percentage of possible data that was recorded during the period was slightly over 80%. Interaction with guest investigators remains at a good level. Now that the phase 3 deep survey is complete, together with the basic data reduction, the scientific analyses are beginning. Some early results should be reported at the Spring AAS meeting. Results from the February 18, 1994 (Olympic) burst and the March 1, 1994 (Chopin [In answer to those who asked why "Chopin", it was his birthday.]) burst will be presented at the Washington APS meeting; those interested in bursts will want to hear this talk. Papers will also be presented at the APS on galactic sources, the galactic diffuse radiation, the search for microsecond bursts, and AGNs. COMPTEL The COMPTEL instrument is performing well and continues routine observations. The anomalies reported earlier associated with the Remote Interface Unit B (RIU-B), external to COMPTEL, which monitors the state-of-health telemetry from the telescope, were eliminated when the Flight Operations Team at Goddard switched the instrument to the redundant RIU-A on March 17. The COMPTEL operations group reports that the switch to RIU-A occurred without problem, and the telescope continues to function normally. The RIU problems had no effect on the quality or quantity of flight data obtained from the instrument. As elsewhere in the gamma-ray community, proposal-preparation activities are reaching a peak within the collaboration, in anticipation of the April 11 deadline for the submission of Cycle 4 GRO proposals to NASA. BATSE BATSE contribution to the GROSSC bi-weekly report: The following was included in IAU Circular 5955: 4U 1145-619 R. B. Wilson, M. H. Finger, M. Stollberg, T. A. Prince, J. M. Grunsfeld, B. A. Harmon, and S. N. Zhang report for the Compton Gamma Ray Observatory BATSE team: "An outburst from an x-ray pulsar is currently being observed. Pulsations were first detected on Mar.12.5 UT. The measured barycentric pulse period was 293.4464 +/-0.0016 s on Mar. 19.0. The location, determined on Mar. 19 using earth-occultation mapping, is R.A. = 11h48m.6, Decl. = -62o03' (equinox 2000.0), with an error radius of 0.2 deg. This location is consistent with either of the transient x-ray binary systems 4U 1145-619 or 1E 1145.1-6141. Based on previously reported periods of 292 and 297 s, respectively, the source is most likely 4U 1145-619. The period rate of change measured between Mar. 17 and 21 was (-2.43 +/- 0.34) x 10E-7. The pulse shape averaged over Mar. 16-20 consists of a narrow peak with a phase width of about 0.35, immediately followed by a deep 'well' with a width of about 0.1 in phase. The total flux in the band 20-40 keV on Mar. 19 was 0.5 Crab. The phase-averaged pulsed flux on that day was 0.3 Crab (total). These flux values each have uncertainties of about 10 percent. The source intensity has remained within 10 percent of these values through Mar. 21.0." The following was included in IAU Circular 5959: GRO J1008-57 M. H. Finger, R. B. Wilson, M. Scott, M. Stollberg, and T. A. Prince report for the Compton Gamma Ray Observatory (CGRO) BATSE pulsar team: "Pulsed hard x-ray flux in the energy range 20-100 keV is currently being detected from the source GRO J1008-57. This source was discovered by CGRO in an outburst in 1993 July (IAUC 5836, 5838) and subsequently observed by ASCA (IAUC 5851) and ROSAT (IAUC 5877). In the current outburst, pulsed flux was first detected on 1994 Mar. 23. The barycentric pulse period of 93.5410 +/- 0.0014 s was determined for Mar. 27.0. The pulse profile consists of a single broad peak, as was previously observed by BATSE. The spectrum of the phase-averaged pulsed flux on Mar. 26 is fit between 20 and 100 keV by an optically-thin thermal bremsstrahlung model of the form A/E exp(-E/kT), with a flux at 45 keV of (1.0 +/- 0.2) x 10E-4 photon cmE-2 sE-1, and kT = 17.9 +/- 4.3 keV. This is about 40 mCrab (total) in the band 20-50 keV. If the interval between this outburst and the last (260 days) is near the orbital period, then a time-of-arrival analysis of the previous outburst requires a projected semi-major axis of 600-800 light seconds, and a mass function of 3-8 solar masses, indicating a high-mass companion." As of March 28th, BATSE has detected 940 cosmic gamma-ray bursts out of a total of 2789 on-board triggers in 1070 days of operation. There have been 729 triggers due to solar flares with emission above 60 keV. Addendum to BATSE report: To guest investigators who propose Earth occultation source measurements using BATSE for Cycle 4: It has been brought to my attention that the Appendix G for NRA 94-OSS-O2 (January, 1994) for the Compton Gamma Ray Observatory has some confusion regarding the figures showing the sensitivity of the Earth occultation technique as applied to the large area BATSE detectors (LADs). In this memo, I would like to correct this confusion for the benefit of Cycle 4 proposers. Figure V-4 on page G-81 is a sensitivity curve for the LADs using the Earth occultation based on early mission measurements and has appeared in previous Appendix G NRAs. The binning shown is for the standard medium energy resolution (MER) data which is obtained continuously at 2.048 sec intervals (CONT data). Figure V-5 on page G-82, despite what is claimed in the figure caption, is the revised sensitivity curve for Earth occultation measurement using an improved measurement algorithm and a longer sampling interval around occultation steps. The binning shown is not the standard CONT channel binning usually used. The 30-50 keV, 50-100 keV, 100-230 keV and 230-600 keV bins in Figure V-5 are normally subdivided into 2 or 3 channels. However, the sensitivity curve is correct for the binning indicated. This figure was also inadvertently placed over another figure of the Crab pulse profile. If you would like to have a postscript file of the figure showing the revised sensitivity with the standard CONT channel binning, you may retrieve via anonymous FTP on grossc.gsfc.nasa.gov, under /nra/cycle4. Alan Harmon Earth Occultation Team Leader, BATSE