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GCN Circular 40615

Subject

GRB 250603A: Swift-XRT position and confirmation of GRB nature

Date

2025-06-03T05:40:03Z (4 days ago)

From

K.L. Page at U Leicester <klp5@leicester.ac.uk>

Via

K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT
team:

The XRT began observing the field of GRB 250603A (GCN Circ. 40613Loading...
 
 ) at
01:12:04.7 UT, 101.7 seconds after the BAT trigger. Using
promptly-collected data (although downlinked after a delay), we find a
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
129.93750, -39.29289 which is equivalent to:
   RA(J2000)  = 08h 39m 45.00s
   Dec(J2000) = -39d 17' 34.4"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 104 arcseconds from the BAT onboard position, within the
BAT error circle.

Given the nature of the fading X-ray light-curve, we confirm this trigger
as GRB 250603A, and not a new Galactic transient.

This circular is an official product of the Swift-XRT team.