TITLE:   GCN CIRCULAR
NUMBER:  30659
SUBJECT: GRB 210818A: Swift-BAT refined analysis
DATE:    21/08/18 21:36:00 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), 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-240 to T+962 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210818A (trigger #1069169)
(Beardmore et al., GCN Circ. 30652).  The BAT ground-calculated position is
RA, Dec = 148.949, -87.029 deg which is
   RA(J2000)  =  09h 55m 47.7s
   Dec(J2000) = -87d 01' 45.3"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.

The mask-weighted light curve shows many overlapping pulses on top of
a general FRED-like structure. The burst emission starts at ~T0, peaks
at ~T+2 s, and ends at ~T+130 s. T90 (15-350 keV) is 73.56 +- 1.55 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.69 to T+128.97 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.22 +- 0.03.  The fluence in the 15-150 keV band is
2.6 +- 0.03 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from
T+1.20 sec in the 15-150 keV band is 11.2 +- 0.4 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.