TITLE:   GCN CIRCULAR
NUMBER:  6649
SUBJECT: GRB 070721B, Further Swift-BAT refined analysis
DATE:    07/07/21 20:44:28 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), H. Ziaeepour (UCL-MSSL)
(on behalf of the Swift-BAT team):
 
Using the data set from T-239 to T+903 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 070721B (trigger #285654)
(Ziaeepour, et al., GCN Circ. 6640; and Palmer, et al., GCN Circ. 6643).
 
Beyond the previously reported description of the mask-weighted lightcurve
(Palmer, 6643), the burst had a second episode of emission with multiple peaks
from T+230 sec to T+380.  We note that there are still gaps in the downlinked
lightcurve data (1: T+530 to T+670, and 2: T+720 to T+830 sec) and as such,
we can not say anything about burst emission in these two intervals.
T90 (15-350 keV) is 340 +- 10 sec (estimated error including systematics).
 
The time-averaged spectrum from T-6.7 to T+359.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.34 +- 0.11.  The fluence in the 15-150 keV band is 3.6 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.19 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.