[vsnet-grb-info 5710] GRB 080307, Preliminary Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7365
SUBJECT: GRB 080307, Preliminary Swift-BAT refined analysis
DATE:    08/03/07 13:52:56 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

D. Palmer (LANL), 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),
T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using only a small amount of data set from the first telemetry downlink
(from T-119 to T+183 sec), we report preliminary analysis of BAT GRB 080307
(trigger #305011) (Holland, et al., GCN Circ. 7362).
The BAT ground-calculated position is RA, Dec = 136.626, 35.156 deg, which is 
   RA(J2000)  = 09h 6m 30.2s 
   Dec(J2000) = 35d 9' 20" 
with an uncertainty of 1.7 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+80 sec.  There is evidence
for emission out to T+135 sec (and the end of the downlinked data ends
at T+183 sec).  T90 (15-350 keV) is 64 +- 22 sec (estimated error
including systematics).
 
Using this partial data set, the time-averaged spectrum from T-7.4 to T+56.6 sec
is best fit by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.41 +- 0.19.  The fluence in the 15-150 keV band is
7.3 +- 0.9 x 10^-7 erg/cm2.  The 1-sec peak photon flux measured from T+16.06 sec
in the 15-150 keV band is 0.2 +- 0.0 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 (= 1.41) is less than 2,
2) The 1-s peak photon flux (= 0.19) is less than 1.0 ph/cm2/s,
3) The light curve variance (= 2.11e-05 is less than 0.0001,
4) The T90/Peak_photon_flux (= 336) 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. 
We must stress however, that we have downlinked data out to only T+180 sec
and there is evidence of continued emissin out to T+135 sec.  So if there
is further activity in this burst past T+180 sec, then the spectral and
temporal values used in this hi-z indicator test may change
and no longer fit the hi-z criteria.  We are publishing this preliminary
refined circular on that chance the hi-z indicator is correct
and follow-up observsers can choose to make observations sooner.

We will issue the regular 'refined' circular when the full data set
becomes available.