TITLE:   GCN CIRCULAR
NUMBER:  39750
SUBJECT: GRB 250316A: Swift-XRT observations
DATE:    25/03/17 00:35:45 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) ,
D.N. Burrows (PSU), M. A. Williams (PSU), J.P. Osborne (U. Leicester)
and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the Swift/BAT
GUANO-detected burst GRB 250316A (GCN #39744), collecting  4.3 ks of
Photon Counting (PC) mode data between T0+21.5 ks and T0+46.5 ks. 

One uncatalogued X-ray source has been detected within the estimated
3-sigma Swift/BAT error region (296 arcsec), it is below the RASS limit
and shows only moderate signs of fading. Therefore, at the present time
we cannot confirm this as the afterglow. Details of this source are
given below:

Source 1:
  RA (J2000.0):  219.5964  =  14:38:23.15
  Dec (J2000.0): +14.8912  =  +14:53:28.2
  Error: 3.1 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0180 [+0.0025, -0.0024] ct s^-1   
  Distance: 118 arcsec from Swift/BAT position.
  Flux: (5.29 [+0.72, -0.70])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)


Four uncatalogued sources were also detected too far from the GRB
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/00021823.

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