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TITLE: GCN CIRCULAR
NUMBER: 9417
SUBJECT: GRB 090520 Swift-BAT detection of a burst in ground analysis
DATE: 09/05/21 21:04:47 GMT
FROM: Jay R. Cummings at NASA/GSFC/Swift
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
On May 20, 2009 at 01:37:16 UT, BAT triggered on GRB 090520
(trigger #352671). The burst was weak, and the instrument
failed to find a source in onboard analysis. A significant
source was found in ground analysis. The source is located at
RA, Dec 11.613, -8.000 deg, which is
RA(J2000) = 00h 46m 27.1s
Dec(J2000) = -08d 00' 00"
with an uncertainty of 3 arcmin (radius, sys+stat, 90%
containment). The partial coding was 48%.
The burst consisted of a single FRED pulse, starting about
T-2 seconds, with a T90 of 20 5 seconds (estimated error
including systematics).
The BAT event data for failed triggers is limited to 10 seconds.
Using 10 seconds of event data from T-2 to T+8 seconds, the
best fit to the spectrum is a simple powerlaw with a photon
index of 0.8 +- 0.2. The fluence for this interval in the
15-150 keV band was 3.4 0.5 x 10-7 ergs/cm2
(68% confidence).
The BAT source position was about 3 arcmin from a low-redshift
galaxy, 6dFGS gJ004613.4-080000. This is an emission-line
galaxy at z = 0.0850.
A Swift TOO was requested, but initially the source was in the
Swift Moon constraint. In any case was 52 degrees (~2.5 hours
in RA) from the Sun, not in constraint, but still an unfavorable
angle, so no Swift followup observation is planned.
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