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GCN Circular 41194

Subject

GRB 250728A: Swift-XRT observations

Event

GRB 250728A

Date

2025-07-29T09:59:23Z (16 days ago)

Edited On

2025-07-29T13:04:01Z (16 days ago)

From

Phil Evans at U of Leicester <pae9@star.le.ac.uk>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of K.L. Page at U Leicester <klp5@leicester.ac.uk>

Via

M.A. Williams (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAR), T.
Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), S. Dichiara (PSU), J.A.
Kennea (PSU) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/GBM-detected burst GRB 250728A, collecting  3.1 ks of Photon
Counting (PC) mode data between T0+14.6 ks and T0+28.2 ks. 

One uncatalogued X-ray source has been detected within the estimated
3-sigma Swift/BAT-GUANO error region (394 arcsec), it is below the RASS limit
and shows no definitive signs of fading. Therefore, at the present time
we cannot confirm this as the afterglow. Details of this source are
given below:

Source 3:
  RA (J2000.0):  260.9895  =  17:23:57.48
  Dec (J2000.0): +16.2004  =  +16:12:01.6
  Error: 6.7 arcsec (radius, 90% conf.)
  Count-rate: (1.98 [+1.26, -0.93])e-3 ct s^-1	 
  Distance: 154 arcsec from Fermi/GBM position.
  Flux: (1.34 [+0.85, -0.63])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Two uncatalogued sources were also detected too far from the BAT
position to be likely afterglow candidates.

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021852.

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