TITLE: GCN CIRCULAR NUMBER: 40877 SUBJECT: GRB 250628B: Swift-XRT observations DATE: 25/06/30 15:04:43 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 GRB 250628B/sb25062804, collecting 1.4 ks of Photon Counting (PC) mode data between T0+2.9 ks and T0+8.9 ks after the trigger. We have detected 2 sources, outside the SVOM/ECLAIRs error circle. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 1 uncatalogued X-ray source * 1 known X-ray source
Uncatalogued X-ray sources --------------------------
Source 2 (SWIFT J221311.1-454427): ================================== RA (J2000.0): 333.2963 = 22h 13m 11.11s Dec (J2000.0): -45.7408 = -45d 44' 26.9" Error: 6.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 12.0 arcmin from the SVOM/ECLAIRs position. Mean rate: (7.7 [+3.9, -3.0])e-3 ct s^-1 Mean flux: (2.9 [+1.5, -1.1])e-13 erg cm^-2 s^-1 Peak rate: (7.7 [+3.9, -3.0])e-3 ct s^-1 Peak flux: (2.9 [+1.5, -1.1])e-13 erg cm^-2 s^-1 ECF: 3.78e-11 erg cm^-2 ct^-1, assuming NH=2.76e+22 cm^-2, gamma=2.97; determined from a spectral fit. RASS UL: 1.0e-01 ct s^-1 (converted to XRT; 0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading.
Known X-ray sources -------------------
Source 1 (SWIFT J221222.2-452220): ================================== RA (J2000.0): 333.0927 = 22h 12m 22.25s Dec (J2000.0): -45.3724 = -45d 22' 20.6" Error: 6.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 11.9 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.0141 [+0.0050, -0.0041] ct s^-1 Mean flux: (3.16 [+1.12, -0.91])e-13 erg cm^-2 s^-1 Peak rate: 0.0141 [+0.0050, -0.0041] ct s^-1 Peak flux: (3.16 [+1.12, -0.91])e-13 erg cm^-2 s^-1 ECF: 2.24e-11 erg cm^-2 ct^-1, assuming NH=1.46e+20 cm^-2, gamma=3.23; determined from a spectral fit. This matches a catalogued X-ray source LSXPS J221222.5-452221 in the LSXPS catalogue. Details: Separation: 3.6" from the XRT source Cat Rate: 2.4e-02 +/- 2.1e-03 ct s^-1 Cat Flux: 5.3e-13 +/- 4.7e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is not above the catalogued flux. There is no evidence for fading. A SIMBAD object `TYC 8438-268-1' is 3.7" away. There is 1 2MASS object within the source's 3-sigma error radius.
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.
We did not detect any sources consistent with the five EP-FXT candidates reported by Zhang et al. (GCN #40874).
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 official product of the Swift-XRT team.
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