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.
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