TITLE: GCN CIRCULAR NUMBER: 42291 SUBJECT: GRB 251013D: Swift-XRT observations DATE: 25/10/15 14:47:57 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

D.N. Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (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 and Swift/BAT-GUANO detected burst GRB 251013D, collecting 4.9 ks of Photon Counting (PC) mode data between T0+71.0 ks and T0+83.7 ks.

Two uncatalogued X-ray sources have been detected within the estimated 3-sigma BAT-GUANO error region (394 arcsec), however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below:

Source 1: RA (J2000.0): 46.8919 = 03h 07m 34.05s Dec (J2000.0): +8.7859 = +08d 47' 09.2" Error: 5.6 arcsec (radius, 90% conf.) Count-rate: (3.42 [+1.17, -0.97])e-3 ct s^-1 Distance: 37 arcsec from Fermi/GBM position. Flux: (1.83 [+1.3, -1.1])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 2: RA (J2000.0): 46.9703 = 03h 07m 52.86s Dec (J2000.0): +8.8156 = +08d 48' 56.0" Error: 6.0 arcsec (radius, 90% conf.) Count-rate: (2.00 [+0.95, -0.74])e-3 ct s^-1 Distance: 331 arcsec from Fermi/GBM position. Flux: (3.4 [+6.2, -1.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Two 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/00021861.

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

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