TITLE:   GCN CIRCULAR
NUMBER:  23047
SUBJECT: GRB 180727A: Swift-BAT refined analysis
DATE:    18/07/28 17:49:10 GMT
FROM:    Hans Krimm at NASA-GSFC/NSF  <hans.krimm@nasa.gov>

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
  
Using the data set from T-239 to T+200 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180727A (trigger #850231)
(Beardmore et al., GCN Circ. 23043).  The BAT ground-calculated position is
RA, Dec = 346.639, -63.066 deg which is
    RA(J2000)  =  23h 06m 33.3s
    Dec(J2000) = -63d 03' 57.9"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
  
The mask-weighted light curve shows a single peak of duration ~1 second,
peaking at T+0 sec. T90 (15-350 keV) is 1.1 +- 0.2 sec (estimated error
including systematics).
  
The time-averaged spectrum from T-0.1 to T+1.3 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.59 +- 0.51,
and Epeak of 67.6 +- 14.8 keV (chi squared 43.23 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.7 +- 0.2 x 10^-7  erg/cm2
and the 1-sec peak flux measured from T-0.05 sec in the 15-150 keV band is
3.6 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.60 +- 0.11 (chi squared 57.46 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level.
  
The duration and hardness of this burst are consistent with the general
BAT short GRB distribution.

The results of the batgrbpoduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/850231/BA/