TITLE:   GCN CIRCULAR
NUMBER:  40565
SUBJECT: GRB 250520A: Swift-BAT refined analysis
DATE:    25/05/28 20:11:35 GMT
FROM:    Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>

R. Gupta (GSFC), S. D. Barthelmy (GSFC), 
R. A. J. Eyles-Ferris (U Leicester), 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), 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+200 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250520A (trigger #1315630)
(Eyles-Ferris, et al., GCN Circ. 40491).  The BAT ground-calculated position is
RA, Dec = 282.265, -11.852 deg which is 
   RA(J2000)  =  18h 49m 03.6s 
   Dec(J2000) = -11d 51' 08.6" 
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.
 
The mask-weighted BAT light curve exhibits a single pulsed emission. 
T90 (15-350 keV) is 0.46 +- 0.15 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.33 to T+0.23 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.55 +- 0.23.  The fluence in the 15-150 keV band is 1.8 +- 0.2 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.54 sec in the 15-150 keV band
is 1.9 +- 0.2 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/1315630