TITLE:   GCN CIRCULAR
NUMBER:  6643
SUBJECT: GRB 070721B, Swift-BAT refined analysis
DATE:    07/07/21 14:22:17 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

D. Palmer (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU), H. Ziaeepour (UCL-MSSL)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+183 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070721B (trigger #285654)
(Ziaeepout, et al., GCN Circ. 6640).  The BAT ground-calculated position is
RA, Dec = 33.128, -2.198 deg  which is 
   RA(J2000)  =  2h 12m 30.8s 
   Dec(J2000) = -2d 11' 54" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 23%.
 
The mask-weighted light curve shows a large main peak starting at ~T-20 sec,
peaking at ~T+0 sec, and ending at ~T+70 sec.  We caution that currently
we only have downlinked data out to T+183 sec, and that there is a hint
of activity past T+70 sec.  But we wanted to get this circular out without
waiting for further downlinks due to the uncertainites given the GCN Notices
problems earlier.  T90 (15-350 keV) is 31.5 +- TTT sec (estimated error
including systematics).
 
The time-averaged spectrum from T-6.7 to T+33.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.31 +- 0.11.  The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.14 sec in the 15-150 keV band
is 1.5 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.