{
  "bibcode": "2025GCN.41644....1E",
  "eventId": "EP250901a",
  "circularId": 41644,
  "subject": "EP250901a: Swift-XRT observations",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "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 EP250901a, collecting 2.0 ks of Photon Counting (PC) mode data between T0+6.2\nks and T0+12 ks after the trigger. We have detected 1 source.  This has been\nautomatically classified as an known X-ray source.\n\nKnown X-ray sources\n-------------------\n\n  Source 1 (SWIFT J181210.9+184216):\n  ==================================\n    RA (J2000.0):   273.0457  =  18 12 10.97\n    Dec (J2000.0):  +18.7047  =  +18 42 16.9\n    Error:\t    5.5 (arcsec, radius, 90% confidence).\n    Detect flag:    GOOD\n    Distance:\t    2.1 arcmin from the Einstein Probe/WXT position.\n    Mean rate:\t    0.0570 +/- 0.0097 ct s^-1\n    Mean flux:\t    (2.06 +/- 0.35)e-12 erg cm^-2 s^-1\n    Peak rate:\t    0.061 +/- 0.015 ct s^-1\n    Peak flux:\t    (2.21 +/- 0.54)e-12 erg cm^-2 s^-1\n    ECF:\t    3.62e-11 erg cm^-2 ct^-1\n\t\t      assuming NH=4.95e+21 cm^-2, gamma=2.27\n\t\t      determined from a spectral fit.\n    This matches a catalogued X-ray source 1RXS J181210.7+184228\n    in the ROSAT/RASSFSC catalogue. Details:\n    Separation:     12.4\" from the XRT source\n    Cat Rate:\t    2.0e-02 +/- 8.7e-03 ct s^-1 \n    Cat Flux:\t    6.7e-13 +/- 2.8e-13 erg cm^-2 s^-1 (0.3-10 keV)\n\t\t      so the source  is 2.5-sigma above the catalogued flux.\n    The source may be fading, at the 0.9-sigma level.\n    A SIMBAD object `1RXS J181210.7+184228' is 12.4\" away.\n    There are 3 2MASS objects 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\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_FIELD00067.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
  "createdOn": 1756765112407,
  "submittedHow": "email"
}