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GCN Circular 3466

Subject
GRB 050525: Swift Detection of a Bright, Possibly Short Burst
Date
2005-05-25T01:36:14Z (19 years ago)
From
David L. Band at NASA/GSFC <dband@lheapop.gsfc.nasa.gov>
D. Band (GSFC/UMBC), J. Cummings (GSFC/NRC), M. Perri
(ASDC), S. Holland (GSFC/USRA), D. N. Burrows (PSU), N.
Gehrels (GSFC), J. E. Hill, J. A. Kennea, S. Hunsberger
(PSU), C. Markwardt (GSFC/UMD), D. Palmer (LANL) on behalf
of the Swift Team.

At 00:02:53 UT, the BAT instrument on the Swift spacecraft
triggered (trigger=130088) and located GRB 050525.  The BAT
on-board calculated location is RA,Dec 278.144 , +26.340
(18h 32m 35s +26d 20' 23") (J2000) with an uncertainty of 3
arcmin (radius, 3-sigma, including systematic uncertainty).
This is a very bright burst, yielding about 1500 counts
over background in 64 ms (preliminary) in the 25-100 keV
range in the BAT instrument.  This would correspond to a
rate of 10 counts/sec/cm2 in that 64 ms interval, but the
peak rate in a later interval may be greater.  Although
light curves are not yet available, the BAT rate trigger
continued to evaluate different timescales while data from
the first 64 ms was being imaged.  The merit parameters
indicate that the highest significance rate trigger is for
a 1 second interval, consistent with a short burst.  More
details will be available after the full data pass.

The XRT was pointed promptly at the burst and took an image
at 00:04:58 UT (125 s after the BAT burst trigger).  The
XRT found a bright X-ray source near the center of the
field of view, with position RA(J2000) = 18h 32m 32.3s
Dec(J2000) = +26d 20' 17.5"  We estimate an uncertainty of
about 6 arcseconds radius (90% containment).  This position
is 31 arcseconds from the BAT position and 8 arcseconds
from the ROTSE position (Rykoff et al, GCN 2465).

We caution that the XRT is in the middle of engineering
tests and is in an unusual mode.  While the X-ray afterglow
looks unusually strong, there are also indications that the
XRT instrument configuration is abnormal due to the tests
being performed.

The XRT position is outside of the UVOT-TDRSS image.
Analysis of the UVOT data will take place after the next
full data pass.

This is a bright burst that appears to be in the short
category; the Sun and moon angles are conducive for optical
observations. Followup observations are strongly
encouraged.
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