{
  "bibcode": "2025GCN.40877....1E",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 40877,
  "body": "P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.\nBeardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.\nBurrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro\n(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato\n(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the\nSwift-XRT team:\n\nSwift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected GRB\n250628B/sb25062804, collecting 1.4 ks of Photon Counting (PC) mode data between\nT0+2.9 ks and T0+8.9 ks after the trigger. We have detected 2 sources, outside the\nSVOM/ECLAIRs error circle. These have been automatically classified as follows:\n  * 0 likely counterparts\n  * 0 candidate counterparts\n  * 1 uncatalogued X-ray source\n  * 1 known X-ray source\n\nUncatalogued X-ray sources\n--------------------------\n\n  Source 2 (SWIFT J221311.1-454427):\n  ==================================\n    RA (J2000.0):  333.2963  =\t22h 13m 11.11s\n    Dec (J2000.0): -45.7408  =\t-45d 44' 26.9\"\n    Error:\t   6.8 (arcsec, radius, 90% confidence).\n    Detect flag:   GOOD\n    Distance:\t   12.0 arcmin from the SVOM/ECLAIRs position.\n    Mean rate:\t   (7.7 [+3.9, -3.0])e-3 ct s^-1\n    Mean flux:\t   (2.9 [+1.5, -1.1])e-13 erg cm^-2 s^-1\n    Peak rate:\t   (7.7 [+3.9, -3.0])e-3 ct s^-1\n    Peak flux:\t   (2.9 [+1.5, -1.1])e-13 erg cm^-2 s^-1\n    ECF:\t   3.78e-11 erg cm^-2 ct^-1, assuming NH=2.76e+22 cm^-2,\n\t\t   gamma=2.97; determined from a spectral fit.\n    RASS UL:\t   1.0e-01 ct s^-1 (converted to XRT; 0.3-10 keV)\n\t so the source is not above this 3-sigma upper limit.\n    There is no evidence for fading.\n\n\nKnown X-ray sources\n-------------------\n\n  Source 1 (SWIFT J221222.2-452220):\n  ==================================\n    RA (J2000.0):  333.0927  =\t22h 12m 22.25s\n    Dec (J2000.0): -45.3724  =\t-45d 22' 20.6\"\n    Error:\t   6.3 (arcsec, radius, 90% confidence).\n    Detect flag:   GOOD\n    Distance:\t   11.9 arcmin from the SVOM/ECLAIRs position.\n    Mean rate:\t   0.0141 [+0.0050, -0.0041] ct s^-1\n    Mean flux:\t   (3.16 [+1.12, -0.91])e-13 erg cm^-2 s^-1\n    Peak rate:\t   0.0141 [+0.0050, -0.0041] ct s^-1\n    Peak flux:\t   (3.16 [+1.12, -0.91])e-13 erg cm^-2 s^-1\n    ECF:\t   2.24e-11 erg cm^-2 ct^-1, assuming NH=1.46e+20 cm^-2,\n\t\t   gamma=3.23; determined from a spectral fit.\n    This matches a catalogued X-ray source LSXPS J221222.5-452221\n    in the LSXPS catalogue. Details:\n      Separation:  3.6\" from the XRT source\n      Cat Rate:    2.4e-02 +/- 2.1e-03 ct s^-1 \n      Cat Flux:    5.3e-13 +/- 4.7e-14 erg cm^-2 s^-1 (0.3-10 keV)\n\t     so the source is not above the catalogued flux.\n    There is no evidence for fading.\n    A SIMBAD object `TYC 8438-268-1' is 3.7\" away.\n    There is 1 2MASS object within the source's 3-sigma error radius.\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits  from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nWe did not detect any sources consistent with the five EP-FXT candidates reported by\nZhang et al. (GCN #40874).\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/SVOM.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
  "createdOn": 1751295883591,
  "subject": "GRB 250628B: Swift-XRT observations",
  "eventId": "GRB 250628B",
  "submittedHow": "email"
}