TITLE:   GCN CIRCULAR
NUMBER:  22658
SUBJECT: GRB 180418A: Swift-BAT refined analysis 
DATE:    18/04/18 22:09:29 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), V. D'Elia (ASDC),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
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 180418A (trigger #826428)
(D'Elia et al., GCN Circ. 22646).  The BAT ground-calculated position is
RA, Dec = 170.132, 24.925 deg which is
  RA(J2000)  =  11h 20m 31.6s
  Dec(J2000) = +24d 55' 28.9"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a single FRED-like pulse that starts
at ~T0, peaks at ~T+0.4 s, and ends at ~T+3.5 s. T90 (15-350 keV)
is 2.29 +- 0.83 sec (estimated error including systematics).

The time-averaged spectrum from T+0.10 to T+3.50 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.44 +- 0.12.  The fluence in the 15-150 keV band is 3.2 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.23 sec in the 15-150 keV band
is 3.0 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The duration and hardness of this burst show it to be intermediate between the
short and long burst populations.

Using a 16-ms binned light curve, the lag analysis finds a lag of 0.1000 +/- 0.026 s
for the 100-350 keV to 25-50 keV band, and 0.088 +/- 0.026 s for the 50-100 keV
to 15-25 keV band. These values are also intermediate between canonical short and
long GRBs.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/826428/BA/