GCN Circular 40255
Subject
GRB 250424A: Swift-BAT refined analysis
Date
2025-04-26T22:48:38Z (a day ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), 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 BAT GRB 250424A (trigger #1306404)
(Cenko, et al., GCN Circ. 40224). The BAT ground-calculated position is
RA, Dec = 217.528, -35.025 deg which is
RA(J2000) = 14h 30m 06.7s
Dec(J2000) = -35d 01' 30.6"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 39%.
The mask-weighted BAT light curve of the burst (began during a slew) shows a faint precursor emission followed by a bright main pulse.
T90 (15-350 keV) is 19.03 +- 1.06 sec (estimated error including systematics), with the T90 starting at T0-20.76 sec due to the slew-delayed T0.
The time-averaged spectrum from T-38.75 to T+262.67 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.54 +- 0.13,
and Epeak of 106.5 +- 33.7 keV (chi squared 47.05 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 3.2 +- 0.1 x 10^-05 erg/cm2
and the 1-sec peak flux measured from T-15.38 sec in the 15-150 keV band is
47.0 +- 1.3 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.79 +- 0.03 (chi squared 58.54 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/1306404