[vsnet-grb-info 21364] GRB 181126A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23463
SUBJECT: GRB 181126A: Swift-BAT refined analysis
DATE:    18/11/27 03:41:42 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), J. P. Norris (BSU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), E. Sonbas (Adiyaman Univ.),
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 181126A (trigger #873539)
(Sonbas et al., GCN Circ. 23453).  The BAT ground-calculated position is
RA, Dec = 152.350, -29.698 deg which is
  RA(J2000)  =  10h 09m 24.0s
  Dec(J2000) = -29d 41' 52.9"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.

The mask-weighted light curve shows two short pulses. The first pulse starts
at ~ T-0.1 s, peaks at ~T0, and ends at ~T+0.2 s. The second pulse starts
at ~T+1.6 s, peaks at ~T+1.8 s, and ends at ~T+2.2 s. T90 (15-350 keV) is
2.09 +- 0.12 sec (estimated error including systematics).

The time-averaged spectrum from T-0.07 to T+2.16 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.13 +- 0.75,
and Epeak of 83.8 +- 24.2 keV (chi squared 66.64 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.1 +- 0.4 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+1.22 sec in the 15-150 keV band is
2.7 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.22 +- 0.15 (chi squared 79.71 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level.

Using the 8-ms binned light curve, the spectral lag for the 100-350 keV to
25-50 keV bands is 26 (+19, -15) ms for the first pulse, and 10 (+21, -13) ms
for the second pulse. These lag values are intermediate between short and
long GRBs, but also are consistent with short GRBs when considering the
large error bars. In addition, no extended emission is found.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/873539/BA/