Compton Observatory Science Report #156 Friday, April 29, 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 function nearly flawlessly. Science Support Center News The 238 Guest Investigator proposals received for Cycle-4 are being processed. Preparation is underway for the peer-review which will take place in late June. A CD Rom containing the Phase-1 EGRET sky survey data is being prepared for distribution at the Minneapolis AAS meeting. Instrument Reports EGRET EGRET operations were normal this biweekly period. The average percentage of possible data recovered remains about 80% or above. Interactions with guest investigators remains at a good level. All EGRET data through period 210 has been transferred to the Compton Observatory Science Support Center in accordance with the planned delivery schedule. As promised two weeks ago, several papers on EGRET results were presented at the APS meeting, including ones on galactic sources, bursts, and AGNs. As expected, the paper on the February 17, 1994 burst, wherein high energy gamma rays were seen for about an hour, and one gamma ray had an energy of 25 GeV, received a substantial amount of attention. This result combined with earlier ones obviously significantly reduces the number of possible explanations of these bursts. Several EGRET publications have appeared recently including one on observations of normal galaxies. The microsecond burst paper and one on pulsars have been accepted for publication in the Astrophysical Journal. OSSE OSSE operations are normal. In viewing period 324 (19-26 Apr), the Z-axis target was the galactic plane near (l,b) = (+20,0) (Key project), and the X-axis target was NGC 7469 (Guest Investigator R. Cameron). When neither target was above the horizon, the target was 4C 15.05. The Sun was near the OSSE scan plane, and the slewing response to BATSE solar flare triggers was enabled. OSSE responded to a flare trigger at TJD 9464.01. In viewing period 325 (26 Apr - 10 May), the Z-axis targets are GT 0236+610 (Guest Investigators M. Coe, M. Tavani) and NGC 1275, and the X-axis targets are QSO 0438-436, PSR 0540-693, and SN 1987A (PI team). The Sun is not available on the scan plane. Data from viewing period 207 were delivered to the Compton GRO Science Support Center archive this week. The targets during this period were IC 4329A and PSR 1822-09. BATSE BATSE contribution to the GROSSC bi-weekly report: The following report was included in IAU Circular 5977: GRO J2014+34 M. H. Finger, Universities Space Research Association; M. Stollberg and G. N. Pendleton, University of Alabama, Huntsville; R. B. Wilson, Marshall Space Flight Center, NASA; and D. Chakrabarty, J. Chiu, and T. A. Prince, California Institute of Technology, report for the Compton Gamma-Ray Observatory BATSE team: "Pulsed hard x-ray emission is being seen from a previously uncatalogued object in the Cygnus-Vulpecula region. The current best-fit source position is R.A. = 20h14m, Decl. = +34o.5 (equinox 2000.0), with an estimated 68-percent-confidence region of radius 8 deg. Work is continuing to verify this position estimate. The emission from the pulsar was first detectable on Apr. 6 and reached peak intensity on Apr. 16. The source is detected at energies from 20 up to at least 70 keV. The barycentric pulse period on Apr. 14.0 UT was 18.7021 +/- 0.0001 s, with the period increasing at a rate of (6.0 +/- 0.7) x 10E-9. The pulse profile averaged over Apr. 14-16 has a main peak with a FWHM of about 0.5 in phase, with a 0.15-HWHM 'shoulder' present on the falling edge. The 20- to 40-keV pulsed flux on Apr. 16 was about 50 mCrab, with the spectrum well fitted by an optically thin thermal bremsstrahlung model F(E) = (A/E)exp(-E/kT), with temperature kT = 23 +/- 6 keV and F(40 keV) = 1.88 +/- 0.24 x 10E-4 photon cmE-2 sE-1 keVE-1." The following has been submitted to as for inclusion as an IAU Circular: HARD X-RAY PULSAR GRO J1948+32 (= GRO J2014+34) D. Chakrabarty and T. A. Prince, Caltech; M. H. Finger, Universities Space Research Association; R. B. Wilson, NASA Marshall Space Flight Center; and G. N. Pendleton, University of Alabama, Huntsville, report for the Compton GRO/BATSE team: "Further observations of the recently discovered 18.7 s transient hard X-ray pulsar in Cygnus (originally designated GRO J2014+34; see IAUC 5977) have yielded a more precise position. The estimated 90-percent-confidence error box is approximately a 2.5 deg x 5.5 deg quadrilateral, with corners RA = 19h58m, Dec = +29 00'; 19h50m, +34 00'; 19h34m, +35 00'; 19h46m, +28 00' (equinox 2000.0). In accordance with the substantially improved position, we have redesignated the source as GRO J1948+32. The pulsed emission was first detectable on Apr. 6 UT and continues to be visible as of Apr. 28. Optical and soft X-ray observations of the error box are strongly encouraged in order to further constrain the X-ray position and identify the accreting companion. As of April 27, BATSE has detected 973 cosmic gamma-ray bursts out of a total of 2846 on-board triggers in 1085 days of operation. There have been 730 triggers due to solar flares with emission above 60 keV. COMPTEL The COMPTEL operations group reports that the instrument is performing well and continues scheduled observations. Ongoing scientific analysis of the available incoming flight data is proceeding routinely at the various COMPTEL sites (i.e., there is nothing terribly extraordinary to report this week). Communications continue with the staff of the Science Support Center regarding the technical details of the installation of the COMPASS analysis package at the SSC. The most exciting upcoming event: preparations are well underway for the GRO/COMPTEL solar eclipse party at the University of New Hampshire on Tuesday, May 10. Weather gods permitting, festivities will begin promptly at 13:42:43 EDT, when the total annular phase begins, and last until 13:44:58 EDT, when totality ends. All friends of GRO and COMPTEL are cordially invited (BYO filters).