{
  "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 source\nGRB 250903A, collecting 2.4 ks of Photon Counting (PC) mode data between T0+12 ks\nand T0+24 ks after the trigger. We have detected 2 sources inside the ECLAIRs error\nregion.  \nThese have been automatically classified as follows:\n  * 0 likely counterparts\n  * 0 candidate counterparts\n  * 2 uncatalogued X-ray sources\n  * 0 known X-ray sources\n\n\nUncatalogued X-ray sources\n--------------------------\n\n  Source 1 (SWIFT J234712.1-755757):\n  ==================================\n    RA (J2000.0):   356.8008  =  23 47 12.19\n    Dec (J2000.0):  -75.9660  =  -75 57 57.6\n    Error:\t    4.3 (arcsec, radius, 90% confidence).\n    Detect flag:    GOOD\n    Distance:\t    2.7 arcmin from the SVOM/ECLAIRs position.\n    Mean rate:\t    0.0387 [+0.0049, -0.0047] ct s^-1\n    Mean flux:\t    (1.33 [+0.17, -0.16])e-12 erg cm^-2 s^-1\n    Peak rate:\t    0.052 +/- 0.014 ct s^-1\n    Peak flux:\t    (1.80 +/- 0.47)e-12 erg cm^-2 s^-1\n    ECF:\t    3.42e-11 erg cm^-2 ct^-1\n\t\t      assuming NH=4.68e+20 cm^-2, gamma=1.95\n\t\t      determined from a spectral fit.\n    XMM UL:\t    2.0e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t      so the source is not above this 3-sigma upper limit.\n    The source may be fading, at the 0.8-sigma level.\n\n  Source 2 (SWIFT J234819.4-755214):\n  ==================================\n    RA (J2000.0):   357.0812  =  23 48 19.49\n    Dec (J2000.0):  -75.8707  =  -75 52 14.5\n    Error:\t    6.4 (arcsec, radius, 90% confidence).\n    Detect flag:    GOOD\n    Distance:\t    4.8 arcmin from the SVOM/ECLAIRs position.\n    Mean rate:\t    (8.6 [+2.9, -2.4])e-3 ct s^-1\n    Mean flux:\t    (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1\n    Peak rate:\t    (8.6 [+2.9, -2.4])e-3 ct s^-1\n    Peak flux:\t    (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1\n    ECF:\t    1.23e-09 erg cm^-2 ct^-1\n\t\t      assuming NH=4.41e+20 cm^-2, gamma=-2.35\n\t\t      determined from a spectral fit.\n    XMM UL:\t    1.9e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t      so the source is 2.7-sigma above this 3-sigma upper limit.\n    There is no evidence for fading.\n    A SIMBAD object `LEDA  242511' is 4.1\" 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\nSource 1 position is consistent with the optical counterpart discovered by TRT (GCN\n41679).\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/SVOM_FIELD00034.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
  "submittedHow": "email",
  "createdOn": 1756993126956,
  "subject": "GRB 250903A: Swift-XRT observations",
  "bibcode": "2025GCN.41699....1E",
  "circularId": 41699,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "eventId": "GRB 250903A"
}