Compton Observatory Science Report #147 Friday, December 22, 1993 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 last of the CGRO reboost burns was successfully completed last week. CGRO is now in a near circular orbit of 452-km apogee by 449-km perigee! A study is planned to determine the expected orbital lifetime and fuel margins for future reboosts. There are now two options: one is to let the orbit decay to 350 km again (estimated at 1997). Another is to maintain the orbit near 450 km. From a lifetime point of view, the maintenance option would give us better fuel efficiency whereas the 350-km option would give us less risk. In any case, we can all rest comfortably and look forward to a long mission. Science Support Center News Several new analysis packages have been ported to the SSC computer systems, and after a period of beta-testing will be available to all Guest Investigators. These are "LIKE", which is a maximum-likelihood point source analysis package developed by the EGRET team, and "WingSpan", which is an interactive (IDL Based) spectral analysis tool. Each of these packages will be available for GI use (via remote login to the SSC) in the near future. An additional BATSE analysis tool, "BFITS" is also undergoing testing at the SSC. It is described in the BATSE Instrument Report below. Details regarding these and other tools will be posted on GRONEWS. The Cycle-4 CRGO Nasa Research Announcement is currently ready for production and will be released in early January. An early April (1994) due date for proposals is planned. Optional electronic submission of proposal forms will be supported by software currently under development at the SSC. This mode of submission, while optional, is encouraged for any proposers with network access, as it ensures the accuracy of transmitted information and greatly facilitates our database maintenance efforts. The submission software will provide the user with letter-quality hard copy of each form as well. Instrument Reports OSSE OSSE operations are normal. The OSSE team is grateful to everyone involved in the very successful and smooth-running reboost operation. Thanks for the extra years in orbit. In viewing period 311.0 and 311.6, the Z-axis target was the Virgo sky survey (Key project) near galactic coordinates (l,b) = (284,+75), and the X-axis target was the radio pulsar PSR 1800-21 (Guest Investigator: J. Cordes). In viewing period 312, the Z-axis target is the Virgo sky survey (Key project) near galactic coordinates (l,b) = (281,+71), and the X-axis target is the galactic plane near 343 degrees longitude (Key project). The Sun is not accessible along the OSSE scan plane, and the slewing response to BATSE solar flare triggers is disabled. Since the last report, there have been no slews to the Sun in response to BATSE flare triggers. Data from viewing periods 24.5 and 30 were delivered to the Compton GRO Science Support Center Archive last week. The targets during vp 24.5 were the galactic plane near 5 degrees longitude, NGC 4151, and NGC 7582. The targets during vp 30 were NGC 2992 and 3C120. EGRET EGRET operations were normal this week. The deep survey continued. Guest Investigator interactions continued at a healthy level. The EGRET team wishes to express their gratitude to everyone involved with the successful reboost operation. COMPTEL The COMPTEL instrument is performing well and continues routine observations. During the final series of reboost maneuvers of the GRO spacecraft from December 15-17, COMPTEL was once again placed in a low-power mode as a safety precaution; the instrument was reactivated without incident on 17 December 1993. The collaboration sends its congratulations and appreciation to the Flight Operations and Flight Dynamics teams at Goddard for their successful completion of the CGRO orbital reboost. The COMPTEL collaboration extends holiday greetings and best wishes for the New Year to all friends and colleagues. BATSE The following report was submitted as an IAU circular item: GRO J1719-24 = GRS 1716-249 B. A. Harmon, NASA/Marshall Space Flight Center, and W. S. Paciesas, University of Alabama in Huntsville, report, for the BATSE/Compton Observatory Team: The hard x-ray transient GRO J1719-24 (=GRS 1716-249), which had been decreasing in intensity at about 0.3% per day from a peak of 1.4 Crab (20-100 keV) on September 30 (IAU Cir #5900), began dropping much more rapidly since approximately December 9. The intensities in the 20-100 keV band for 10, 13, and 15 December were 1.1 (+/-10%), 0.9(+/-15%), and 0.4(+/-20%) Crab, respectively. On December 16-18 the source dropped below the BATSE 3-sigma one-day detection limit of 0.1 Crab. Preliminary indications showed no marked change in spectral shape during the intensity decrease. Observations in other wavelength bands are strongly encouraged. The Program BFITS has been delivered to the GROSSC and is being installed. BFITS is a FITS-format file generating program that operates upon BATSE Individual Burst DataBase (IBDB) files. It takes data stored in different formats and aligns them into a consecutive time history of count rates and errors. BFITS also provides the current best calculation for the energy edges of the data bins, and includes calibration information for future channel-to- energy conversion routines. Positional information is stored for the source and the Earth at the time of the BATSE trigger, so that a detector response matrix can be generated with only a BFITS file as input. BFITS operates under the TAE menuing system (TUTOR mode), and provides detailed help for each of its subcommands and parameters. The BATSE team recommends that burst investigators use BFITS rather then directly reading the IBDB's. IBDB's for 42 solar flares and 136 gamma-ray bursts were delivered to the science support center two weeks ago and should soon be available.