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GCN Circular 21384

Subject
GRB 170728B, Swift-BAT refined analysis
Date
2017-07-29T19:04:42Z (7 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170728B (trigger #765130)
(Cenko et al., GCN Circ. 21371Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 238.019, 70.111 deg which is
  RA(J2000)  =  15h 52m 04.5s
  Dec(J2000) = +70d 06' 40.0"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 5%.

The mask-weighted light curve shows a short multi-peaked structure from
~T-0.1 s to ~T+0.7 s, followed by some weak emission till ~T+50 s,
Fermi/GBM also reports emission till ~T+47 s (Stanbro et al., GCN Circ. 21383Not found
 
 
).
T90 (15-350 keV) is 47.7 +- 25.2 sec (estimated error including systematics).

The time-averaged spectrum for the short pulse from T-0.1 to T+0.7 sec is
best fit by a power law with an exponential cutoff.  This fit gives a photon
index -1.10 +- 1.71, and Epeak of 82.0 +- 24.2 keV (chi squared 51.71 for
56 d.o.f.).  For this model the total fluence in the 15-150 keV band is
6.2 +- 1.1 x 10^-7 erg/cm2. A fit to a simple power law gives a photon index
of 1.21 +- 0.24 (chi squared 61.25 for 57 d.o.f.).

The time-averaged spectrum for the extended emission from T+0.7 to T+50.6 sec is
best fit by a simple power-law model.  The power law index of the time-averaged
spectrum is 2.25 +- 0.57.  The fluence in the 15-150 keV band is
9.8 +- 3.9 x 10^-7 erg/cm2.

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/765130/BA/