TITLE: GCN CIRCULAR NUMBER: 40679 SUBJECT: GRB 250610B: Swift-XRT counterpart detection DATE: 25/06/10 23:55:14 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250610B, collecting 2.0 ks of Photon Counting (PC) mode data between T0+2.8 ks and T0+8.9 ks after the trigger. A likely counterpart has been found consistent with the optical detection (GCN Circ. 40676, 40677 and 40678). The details of this source are:
Source 1 (SWIFT J132043.2+310614): ================================== RA (J2000.0): 200.1802 = 13h 20m 43.25s Dec (J2000.0): +31.1040 = +31d 06' 14.4" Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.3 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.1084 +/- 0.0084 ct s^-1 Mean flux: (3.91 +/- 0.30)e-12 erg cm^-2 s^-1 Peak rate: 0.134 +/- 0.022 ct s^-1 Peak flux: (4.85 +/- 0.81)e-12 erg cm^-2 s^-1 ECF: 3.61e-11 erg cm^-2 ct^-1, assuming NH=1.44e+20 cm^-2, gamma=1.78; determined from a spectral fit. XMM UL: 2.4e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.0-sigma above this 3-sigma upper limit. There is no evidence for fading.
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
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/SVOM.
This circular is an officicial product of the Swift-XRT team.
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