[vsnet-grb-info 5747] GRB 080310, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7402
SUBJECT: GRB 080310, Swift-BAT refined analysis
DATE:    08/03/10 21:21:53 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <jayc at milkyway.gsfc.nasa.gov>

J. Tueller (GSFC),
S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC),
E. Fenimore (LANL),
N. Gehrels (GSFC),
H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD),
K. McLean (GSFC/UMD),
D. Palmer (LANL),
A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU),
T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080310 (trigger #305288)
(Cummings, et al., GCN Circ. 7382).  The BAT ground-calculated position is
RA, Dec = 220.040, -0.164 deg which is
   RA(J2000)  = 14h 40m 9.6s
   Dec(J2000) = 0d 9' 49"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.
 
The mask-weighted lightcurve shows many peaks starting at ~T-60 sec.  The
main peak extends from ~T-12 to T+7 sec, then there is a period with no
detectable emission, then a broad, weaker peak from T+180 to T+360 sec.
The later peak corresponds to the first strong flare seen in the XRT (Beardmore
et al., GCN circ. 7399).  BAT sees no emission at the time of the second flare
seen in the XRT, even though in the XRT energy range it was of similar intensity
at the peak to the first flare.

The location of the burst entered the BAT field of view at about T-80 sec during
a preplanned slew.  It is possible that some very weak emission preceded that
time, but the BAT raw lightcurve, which is partially sensitive to photons from
outside the FOV rules out strong emission. T90 (15-350 keV) is 365 +- 20 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-71.8 to T+318.7 sec is best fit by a simple
power-law model.  The burst does not appear to have significant emission above
about 150 keV however.  The power law index of the time-averaged spectrum is
2.32 +- 0.16.  The fluence in the 15-150 keV band is 2.3 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+1.27 sec in the 15-150 keV band
is 1.3 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/305288/BA/