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GCN Circular 1442

Subject
GRB020625 (=H2081): A Long Burst Localized by HETE
Date
2002-06-25T22:00:39Z (22 years ago)
From
Don Lamb at U.Chicago <lamb@oddjob.uchicago.edu>
G. Ricker, J-L Atteia, N. Kawai, D. Lamb, and S. Woosley on behalf of
the HETE Science Team;

N. Butler, J. Doty, R. Vanderspek, J. Villasenor, G. Crew, G. Monnelly,
T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G. Prigozhin,
J. Braga, R. Manchanda, and G. Pizzichini, on behalf of the HETE
Operations and HETE Optical-SXC Teams;

Y. Shirasaki, C. Graziani, M. Matsuoka, T. Tamagawa, K. Torii,
T. Sakamoto, A. Yoshida, E. Fenimore, M. Galassi, T. Tavenner, and
T. Donaghy, on behalf of the HETE WXM Team;

M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf of the HETE
FREGATE Team;

write:


At 11:25:49.32 UTC (41149.32 s UT) on 25 June 2002, the HETE FREGATE
instrument detected event H2081.  This event, which triggered FREGATE
in Band C (30-400 keV), was very hard:  the event is strongly evident
(SNR ~ 12) in FREGATE Band C and is evident in FREGATE Band B (6-80
keV), but is barely visible, if at all, in FREGATE Band A (6-40 keV)
and in the WXM 2-25 keV energy band.

A second event occurred 86 sec later.  This event was much softer: it
is barely visible in FREGATE Band C, but is discernible in FREGATE
bands A and B.  This second event is also strongly evident in the WXM
2-25 keV energy band (SNR ~ 8).  Triggers on the WXM data are currently
off in order to avoid inundating the astronomical community with XRB
triggers, and therefore no WXM flight location was calculated for this
event.

The probability of the HETE FREGATE and WXM instruments detecting two
separate GRBs within 100 sec is very small.  We therefore interpret
the two events as part of a single, long GRB, consisting of two main
peaks and having a duration > 125 sec.

No real-time spacecraft aspect was available because of the full moon
(99% illumination).  Ground analysis produced a location, using the
spacecraft aspect at the time of trigger H2081 (corresponding to the
beginning of the first peak), that was reported in a GCN Position
Notice at 14:19:24 UT, 173 min after the burst.  Further ground
analysis revealed that the spacecraft had drifted by an unusually large
amount (~10 arcminutes) during the burst.  Therefore a refined
location, using the spacecraft aspect at the time of the second peak,
which could be localized using WXM data, was reported in a second GCN
Position Notice at 15:16:17 UT, 230 min after the burst.  The refined
location can be expressed as a 90% confidence rectangle that is 18
arcminutes by 32 arcminutes.  The center and the corners of the
rectangle lie at the following J2000 coordinates:

RA = 20h 44m 14s, Dec = +07o 10' 12" (center)
RA = 20h 43m 09s, Dec = +07o 18' 32" (corner)
RA = 20h 44m 08s, Dec = +07o 28' 08" (corner)
RA = 20h 45m 20s, Dec = +07o 01' 52" (corner)
RA = 20h 44m 21s, Dec = +06o 52' 16" (corner).


The first peak of GRB020625 had a peak flux >6 Crab and a duration of
~20 sec in  FREGATE Band C (30-400 keV), during which a total of 1200
net counts were detected.  The second peak had a peak flux ~2.0 x 10^-8
ergs cm-2 s-1 (i.e., ~1 x Crab flux) averaged over 1.2 sec and a
duration of ~17 sec in FREGATE Band A (6-40 keV).  During this time
interval a total of 830 net counts were detected, corresponding to a
fluence of ~1.5 x 10^-7 ergs cm-2.  In the WXM 2-25 keV band, the
second peak had a duration of 25 seconds.  The WXM localization SNR
was ~9.

Further information (including a light curve) for GRB020625 is provided
at the following URL:

http://space.mit.edu/HETE/Bursts/

This message is citable.
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