GCN Circular 35861

S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
T. Sakamoto (AGU) (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 Swift J151857.0-572147 (trigger #1218452)
(Lien et al., GCN Circ. 35849
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 229.773, -57.364 deg which is
   RA(J2000)  =  15h 19m 05.5s
   Dec(J2000) = -57d 21' 50.8"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 86%.

The mask-weighted light curve shows a consistent emission throughout
the entire time interval when the source was in the BAT FOV from
T-127 s to T+798 s. In addition, BAT triggered on this source
again on March 4th at 08:53 UT (Ambrosi et al., GCN Circ. #35858),
indicating that the source is still detectable in BAT.
The BAT transient monitor shows that the source started to
appear on March 3rd.

The time-averaged spectrum from T-83.64 to T+753.64 sec is best
fit by a power law with an exponential cutoff.  This fit gives
a photon index 1.72 +- 0.44, and Epeak of 14.0 +- 10.1 keV
(chi squared 72.90 for 56 d.o.f.).  For this model the total
fluence in the 15-150 keV band is 5.7 +- 0.4 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T-80.60 sec in the
15-150 keV band is 0.4 +- 0.2 ph/cm2/sec.  A fit to a simple
power law gives a photon index of 2.48 +- 0.11 (chi squared 79.64
for 57 d.o.f.).  All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1218452

The BAT transient monitor page for this source will be available at
https://swift.gsfc.nasa.gov/results/transients/weak/SwiftJ1518-5721/