GCN Circular 39617

T. Parsotan (GSFC), S. D. Barthelmy (GSFC),

P. A. Evans (U Leicester), R. Gupta (GSFC),

H. A. Krimm (NSF), S. Laha (GSFC/UMBC),

A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),

M. J. Moss (GSFC), D. M. Palmer (LANL),

D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)

(i.e. the Swift-BAT team):


Using the data set from T-240 to T+961 sec from the recent telemetry downlink,

we report further analysis of BAT GRB 250306A (trigger #1293340)

(Evans et al., GCN Circ. 39606
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 ).  The BAT ground-calculated position is

RA, Dec = 354.724, -47.998 deg which is

   RA(J2000)  =  23h 38m 53.7s

   Dec(J2000) = -47d 59' 52.8"

with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 13%.


The mask-weighted BAT light curve shows a distinct peak at around BAT trigger time,
 
followed by a rapid decay and a quieter post-peak phase. 

T90 (15-350 keV) is 11.44 +- 2.44 sec (estimated error including systematics).


The time-averaged spectrum from T-1.52 to T+19.04 sec is best fit by a power law

with an exponential cutoff.  This fit gives a photon index 0.87 +- 0.24,

and Epeak of 132.8 +- 45.6 keV (chi squared 62.11 for 56 d.o.f.).  For this

model the total fluence in the 15-150 keV band is 8.9 +- 0.3 x 10^-06 erg/cm2

and the 1-sec peak flux measured from T+0.18 sec in the 15-150 keV band is

35.9 +- 1.6 ph/cm2/sec.  A fit to a simple power law gives a photon index

of 1.37 +- 0.05 (chi squared 75.58 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/1293340