GCN Circular 3512

E. Fenimore (LANL), L. Angelini (GSFC-JHU)L. Barbier (GSFC),
S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC),
J. Greiner (MPE), D. Hullinger (UMD), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
A. Retter (PSU) T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
M. Suzuki (Saitama), J. Tueller (GSFC)
on behalf of the Swift/BAT team:

At 06:29:05.2 UT, Swift-BAT detected GRB 050603 (trigger=131560)
(GCN Circ 3509
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 , Retter et al.). The refined BAT ground position
is (RA,Dec) = 39.982,-25.195, [deg; J2000] {02:39:56;  -25:11:41}
(~1 arcminute statistical and systematic error radius, 
95% containment).   This is about  45 arcseconds from the
on-board derived position.  This source was near the edge of
the field of view, 41 degrees from the boresight in the
short direction, directly illuminating only 9% of the
detector array.

The mask-weighted lightcurve of the burst shows three
fast-rise-exponential-decay (FRED) spikes, peaking at 
T-2.7, T-0.85 and T+0.15 with each spike having a width 
of ~0.6 s (FWHM). The third spike is ~3x the height of each of 
the first two spikes and produced the original image detection.
Additional tail emission continues to decay after the third
spike, extending to T+10.

The photon index of the time-averaged spectrum is well-fit
over the 15-350 keV energy band  by a power law of index
1.22 +/- 0.06 with a normalization at 50 keV of 
(2.96 +/- 0.10) x 10^-2 photons/s/cm^2/keV. The fluence
in the 15-350 keV band is 1.30 x 10^-5 erg/cm^2. The peak
flux is 31.8+/1.7 photons/cm^2/s for the 1 second interval
starting at T-0.18 s.

Due to the current engineering mode of the spacecraft, 
XRT and UVOT observations will be delayed until a 
Target Of Opportunity pointing is manually commanded.