GCN Circular 7673

T. Ukwatta (GWU), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
J. Mao (INAF-OAB), D. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080503 (trigger #310785)
(Mao, et al., GCN Circ. 7665
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 286.686, 68.803 deg, which is 
   RA(J2000)  =  19h 06m 44.7s 
   Dec(J2000) = +68d 48' 09.2" 
with an uncertainty of 3.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 75%.
 
The mask-weighted light curve shows an initial spike starting at ~T+0.1 sec
with a fast rise to a peak at ~T+0.2 sec, with a roughly exponential decay
down to background at ~T+0.7 sec.  The softer emission starts at about T+10 sec,
rising with two peaks at about T+26 and +37 sec, and then falling to background
levels at T+220+/-20 sec.  T90 (15-350 keV) is 170 +- 40 sec (estimated error
including systematics).
 
The time-averaged spectrum from T+0.2 to T+220.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.00 +- 0.13.  The fluence in the 15-150 keV band is 2.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+26.58 sec in the 15-150 keV band
is 0.9 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence level.

As to whether this burst is a SHB with extended emission or a Long burst
with a particularly short pulse at the beginning, we can not say yet.  Looking
at the 4-band lightcurves, the initial spike is harder than the later emission.
We are waiting for (a) separate spectral analysis on the two portions
of the lightcurve, and (b) for the lag analysis.  We are currently in an 8-hour
gap in the downlink sessions, so it will be a while before we can say
with better confidence if this is truely a SHB or not.  We will issue
another circular.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/310785/BA/