Repeating Gamma-ray SourceDec 10, 1996
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GAMMA-RAY BURSTSC. Meegan, V. Connaughton, G. Fishman (NASA/MSFC), R. M. Kippen (UAH), C. Kouveliotou (USRA), K. Hurley (UC Berkeley), T. Cline, D. Palmer, S. Barthelmy, P. Butterworth, B. Teegarden, H. Seifert, J. in 't Zand (NASA/GSFC), E. Mazets, S. Golenetskii (IOFFE) report:
Several spacecraft have detected a sequence of gamma-ray bursts over a two day period whose locations are consistent with a single source. The following table gives the times of the events, the BATSE determined location with its statistical uncertainty, an approximate duration, and the spacecraft that detected the event.
The DIST column shows the proximity (where sigma is the quadrature sum of the statistical errors and does not include BATSE's ~1.6 deg systematic error) of the first three BATSE event locations to the fourth which has the best determined position, including Interplanetary (IPN) locations using BATSE, Ulysses and Konus. The Ulysses-BATSE IPN annulus is described by a center at RA=356.657 and DEC=-31.408 (J2000) with a radius of 49.883 deg, full width 0.078 deg. The much wider Ulysses-Konus annulus defines the end-points of the Ulysses-BATSE annular segment at RA=59.73, DEC=-47.07 and RA=60.32, DEC=-52.58 with a 99.7% confidence level. A soft gamma repeater (SGR) can be excluded as a common source by the durations of the events, as well as by their spectra, which are consistent with classical gamma-ray bursts. The temporal structures of the events are quite different, apparently ruling out a gravitational lens interpretation. The third and fourth events are very probably separate triggers from a single burst, making the combined event the longest burst (1420 sec) ever seen in this energy range. Although a posteriori calculations are problematic, the probability of such a temporal and spatial coincidence of four unrelated events is low.
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