Central Bureau for Astronomical Telegrams
IAUC 6743: Poss. NEW SOFT gamma-RAY REPEATER
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Circular No. 6743
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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POSSIBLE NEW SOFT gamma-RAY REPEATER
K. Hurley, Space Sciences Laboratory, Berkeley, on behalf of
the Ulysses Gamma-Ray Burst Team; C. Kouveliotou, Universities
Space Research Association (USRA), on behalf of the Gamma-Ray
Observatory BATSE team; and T. Cline and E. Mazets, on behalf of
the KONUS-WIND team, report: "Ulysses has observed three similar
short intense bursts whose triangulated positions are consistent
with a single location. The first two occurred on June 29 (and
were also observed by KONUS-WIND), and the third on Sept. 12; the
second and third are the BATSE triggers described below. For each
burst, we can derive a single annulus of possible arrival
directions. They intersect over a region defined by the following
coordinates (equinox 2000.0): R.A. = 18h14m50s, Decl. = -13o36'.6;
18h14m25s, -14o01'.7; 18h15m26s, -13o15'.0; 18h15m02s, -13o39'.8."
C. Kouveliotou, USRA and Marshall Space Flight Center (MSFC),
NASA; G. J. Fishman and C. A. Meegan, MSFC; and P. Woods,
University of Alabama in Huntsville, report on behalf of the BATSE
Team: "BATSE triggered on two very intense, short, soft events on
June 29.27189 and Sept. 12.25652 UT. Each lasted about 2 s, and
their (preliminary) spectra can be fitted with a power-law with
indices of about -3.8 and -4.2, respectively. Given the
characteristics and common location noted above, we classify them
as soft-gamma-ray-repeater events from a previously unknown source."
D. A. Smith, A. M. Levine, E. H. Morgan, and R. A. Remillard,
Massachusetts Institute of Technology (MIT), on behalf of the
RXTE/ASM team at MIT and Goddard Space Flight Center, NASA; and R.
Rutledge, Max-Planck-Institut fur Extraterrestrische Physik, write:
"The RXTE All Sky Monitor has detected the Sept. 12 event reported
above; ASM camera 3 detected a bright x-ray flash that lasted about
2.8 s and yielded a peak countrate of about 270 counts/s. The
inferred peak flux, including corrections for background and
location in the field-of-view, is about 10 Crab (2-12 keV). We
obtain a single long, narrow line of position. Our formal analysis
gives an error box with corners at R.A. = 18h25m39s.0, Decl. =
-14o51'48"; 18h25m42s.6, -14o48'50"; 18h34m24s.9, -15o28'10";
18h34m04s.5, -15o23'31" (equinox 2000.0). However, the
determination of the ends of the error box along the long direction
is subject to systematic errors of about 2 deg. With this
consideration, the extension of our error box by about 2.8 deg in
the long direction is consistent with the intersection of the
position annuli from the IPN reported above. The combined IPN/ASM
error box is centered at R.A. = 18h14m.7, Decl. = -13o40' and has a
radius (90-percent confidence) of 5'."
(C) Copyright 1997 CBAT
1997 September 13 (6743) Daniel W. E. Green
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