TITLE: GCN CIRCULAR NUMBER: 39998 SUBJECT: GRB 250331D: Swift-XRT observations DATE: 25/04/01 08:59:42 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (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-detected burst GRB 250331D, collecting 5.3 ks of Photon Counting (PC) mode data between T0+45.2 ks and T0+68.1 ks. Two uncatalogued X-ray sources have been detected within the estimated 3-sigma Swift/BAT error region (493 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 2: RA (J2000.0): 48.6572 = 03:14:37.72 Dec (J2000.0): +62.2833 = +62:16:59.7 Error: 3.5 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (7.4 [+1.6, -1.4])e-3 ct s^-1 Distance: 235 arcsec from Swift/BAT position. Flux: (3.18 [+0.67, -0.61])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 4: RA (J2000.0): 48.7705 = 03:15:4.93 Dec (J2000.0): +62.3734 = +62:22:24.1 Error: 5.9 arcsec (radius, 90% conf.) Count-rate: (1.77 [+0.95, -0.72])e-3 ct s^-1 Distance: 476 arcsec from Swift/BAT position. Flux: (1.19 [+0.64, -0.49])e-10 erg cm^-2 s^-1 (observed, 0.3-10 keV) A catalogued source was also detected within the estimated 3-sigma Swift/BAT error region (493 arcsec). 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/00021825. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...