{
  "subject": "EP250831a: Swift-XRT observations",
  "circularId": 41624,
  "submittedHow": "email",
  "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 Einstein Probe/WXT-detected\nsource EP250831a, collecting 1.8 ks of Photon Counting (PC) mode data between T0+24\nks and T0+30 ks after the trigger. We have detected 1 source 4.6 arcmin from the WXT\nposition, somewhat outside the 90% error region of 2.9 arcmin (GCN 41619).  This has\nbeen automatically classified as an uncatalogued X-ray source.\n\nUncatalogued X-ray sources\n--------------------------\n\n  Source 1 (SWIFT J025130.9-360728):\n  ==================================\n    RA (J2000.0):   42.8789  =\t02 51 30.94\n    Dec (J2000.0):  -36.1245  =  -36 07 28.2\n    Error:\t    5.0 (arcsec, radius, 90% confidence).\n    Detect flag:    GOOD\n    Distance:\t    4.6 arcmin from the Einstein Probe/WXT position.\n    Mean rate:\t    (7.6 [+2.8, -2.3])e-3 ct s^-1\n    Mean flux:\t    (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1\n    Peak rate:\t    (7.6 [+2.8, -2.3])e-3 ct s^-1\n    Peak flux:\t    (1.97 [+0.73, -0.59])e-13 erg cm^-2 s^-1\n    ECF:\t    2.58e-11 erg cm^-2 ct^-1\n\t\t      assuming NH=3.05e+20 cm^-2, gamma=2.54\n\t\t      determined from a spectral fit.\n    LSXPS UL:\t    1.7e-02 ct/sec, (0.3-10 keV)\n\t\t      so the source is not above this 3-sigma upper limit.\n    There is no evidence for fading.\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\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/EP/EP_FIELD00066.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
  "createdOn": 1756701575901,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "bibcode": "2025GCN.41624....1E",
  "eventId": "EP250831a"
}