[vsnet-grb-info 5718] GRB 080307, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7373
SUBJECT: GRB 080307, Swift-BAT refined analysis
DATE:    08/03/07 18:47:06 GMT
FROM:    Goro Sato at GSFC  <gsato at milkyway.gsfc.nasa.gov>

G. Sato (GSFC/ISAS), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), S. T. Holland (CRESST/USRA/GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), 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 080307 (trigger #305011)
(Holland, et al., GCN Circ. 7362, and Palmer, et al., GCN Circ. 7365).
The BAT ground-calculated position is RA, Dec = 136.629, 35.151 deg
which is
    RA(J2000)  = 9h 6m 31.0s
    Dec(J2000) = 35d 9' 4"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 81%.

The mask-weighted light curve shows an initial FRED-like peak
starting at T+0 sec, and ending around T+140 sec.  A strong spectral
evolution can be seen in the BAT four energy band light curves.
T90 (15-350 keV) is 125.9 +- 24.6 sec (estimated error including
systematics).

The time-averaged spectrum from T+1.7 to T+146.1 sec is best fit by a
simple power-law model.  The power law index of the time-averaged
spectrum is 1.78 +- 0.21.  The fluence in the 15-150 keV band is
8.7 +- 1.2 x 10^-07 erg/cm2.  The 1-sec peak photon flux measured from
T+1.90 sec in the 15-150 keV band is 0.4 +- 0.1 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/305011/BA/

This burst satisfies Sakamoto/Ukwatta Swift-BAT possible high-z criteria
(Ukwatta et al. arXiv:0802.3815):
1) The power law photon index (= 1.78) is less than 2,
2) The 1-s peak photon flux (= 0.4) is less than 1.0 ph/cm2/s,
3) The light curve variance (= 9.4e-06) is less than 0.0001,
4) The T90/Peak_photon_flux (= 350) is greater than 100.
Based on a limited sample of bursts, these criteria yield
an 85% chance it has a redshift greater than 3.5.