TITLE:   GCN CIRCULAR
NUMBER:  23384
SUBJECT: GRB 181027A: Swift-BAT refined analysis
DATE:    18/10/27 13:06:40 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto@phys.aoyama.ac.jp>

S. D. Barthelmy (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), 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 181027A (trigger #868984)
(Lien, et al., GCN Circ. 23383).  The BAT ground-calculated position is
RA, Dec = 225.361, 30.937 deg which is
    RA(J2000)  =  15h 01m 26.7s
    Dec(J2000) = +30d 56' 12.6"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
  
The mask-weighted light curve shows a weak emission followed by a bright peak.
The emission starts at T-18.4 sec, peaks at T+47.5 sec and ends at T+85.4 sec.
T90 (15-350 keV) is 81.16 +- 10.55 sec (estimated error including systematics).

The time-averaged spectrum from T-18.45 to T+85.44 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.42 +- 0.09.  The fluence in the 15-150 keV band is 2.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+47.81 sec in the 15-150 keV band
is 1.2 +- 0.2 ph/cm2/sec.  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/868984/BA/