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GCN Circular 40812

Subject

GRB 250617B: Swift-BAT refined analysis

Event

GRB 250617B

Date

2025-06-23T11:39:14Z (a day ago)

From

Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>

Via

Web form

S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Gupta (GSFC),
H. A. Krimm (NSF), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), K. L. Page (U Leicester),  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-273 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250617B (trigger #1325580)
(Page, et al., GCN Circ. 40760Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 332.883, 32.721 deg which is
   RA(J2000)  =  22h 11m 31.8s
   Dec(J2000) = +32d 43' 14.5"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 10%.

The mask-weighted light curve shows two peaks.  The emission starts at
T-30 sec, peaks at T+1 sec, and ends at T+18 sec.
T90 (15-350 keV) is 36.5 +- 6.9 sec (estimated error including systematics).

The time-averaged spectrum from T-29.32 to T+14.30 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.13 +- 0.22.  The fluence in the 15-150 keV band is 2.3 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band
is 2.9 +- 0.8 ph/cm2/sec.  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/1325580