[vsnet-grb-info 20984] GRB 180805B: Swift-BAT refined analysis (short GRB with extended emission)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23082
SUBJECT: GRB 180805B: Swift-BAT refined analysis (short GRB with extended emission)
DATE:    18/08/06 02:00:36 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. D'Avanzo (INAF-OAB),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
D. M. Palmer (LANL), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (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 180805B (trigger #851855)
(D'Avanzo et al., GCN Circ. 23076).  The BAT ground-calculated position is
RA, Dec = 25.877, -17.475 deg which is
  RA(J2000)  =  01h 43m 30.6s
  Dec(J2000) = -17d 28' 29.3"
with an uncertainty of 3.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.

The mask-weighted light curve show a short pulse that starts from ~T-0.1 s,
peaks at ~T+0.1 s, and ends at ~T+0.7 s. The short pulse is followed by
some weak emission that lasts until ~ T+130 s. T90 (15-350 keV) is
122.5 +- 18.3 sec (estimated error including systematics).

The time-averaged spectrum from T-0.10 to T+127.46 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.13 +- 0.29.  The fluence in the 15-150 keV band is 9.6 +- 1.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.11 sec in the 15-150 keV band
is 1.7 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The structure of the burst shows similarity to those of short GRBs with
extended emission. We thus perform further analysis on the short spike and the
tail emission.

The spectrum of the short pulse from T-0.001 to T+0.712 sec can be fitted by
a simple power-law model with power-law index of 0.66 +- 0.20 and
fluence (15-150 keV) of 1.7 +- 0.2 x 10^-7 erg/cm2. The spectrum of the
extended emission from T+0.712 to T+126.532 sec is best fit by a simple power-law
model, with power-law index of 1.16 +- 0.39 and fluence (15-150 keV) of
6.8 +- 1.6 x 10^-7 erg/cm2. These values are consistent with those of short GRBs
with extended emission (Lien & Sakamoto et al. 2016).

The lag analysis does not produce a well-constrained value due to the weakness
of the short pulse.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/851855/BA/