TITLE:   GCN CIRCULAR
NUMBER:  18196
SUBJECT: GRB 150821A, Swift-BAT refined analysis
DATE:    15/08/22 15:32:50 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC),  J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
E. Troja (NASA/GSFC/UMCP), T. N. Ukwatta (LANL)
(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 150821A (trigger #652847)
(Troja, et al., GCN Circ. 18186).  The BAT ground-calculated position is
RA, Dec = 341.913, -57.883 deg which is
  RA(J2000)  =  22h 47m 39.0s
  Dec(J2000) = -57d -52' -58.7"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 1.5%.

Due to the low partial coding fraction of this burst, the light curves and
burst durations are created using the special DETECTION mask aperture.
However, the spectral analysis are done using the default FLUX aperture
for more accurate results, and thus the spectral analysis is only available
after T0+174.24 s, when the burst came into the BAT calibrated field of view.
Note that the interval used for the spectral analysis included < 1% of the
total fluence.

The  mask-weighted light curve starts at ~T0+20 s and contains several
overlapping pulses. The main structure ends at ~T0+70 s, with a long-lasting
tail until ~T0+330 s. T90 (15-350 keV) is 172.1 +- 99.0 sec (estimated error
including systematics).

The time-averaged spectrum from T+174.2 to T+330.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.10 +- 0.37.  The fluence in the 15-150 keV band is 7.9 +- 1.9 x 10^-7 erg/cm2.
The 1-s peak spectral analysis is unavailable because the 1-s peak duration
happens before the burst came into the BAT calibrated field of view.
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/652847/BA/