{
  "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 EP#01709178975, collecting 594 s of Photon Counting (PC) mode data between\nT0+2.1 ks and T0+2.8 ks after the trigger. A candidate counterpart has been found.\nThe details of this source are:\n\n  Source 1 (SWIFT J154403.9-331113):\n  ==================================\n    RA (J2000.0):  236.0166  =\t15h 44m 03.98s\n    Dec (J2000.0): -33.1871  =\t-33d 11' 13.6\"\n    Error:\t   3.6 (arcsec, radius, 90% confidence).\n    Detect flag:   GOOD\n    Distance:\t   52 arcsec from the Einstein Probe/WXT position.\n    Mean rate:\t   1.079 +/- 0.065 ct s^-1\n    Mean flux:\t   (3.14 +/- 0.19)e-11 erg cm^-2 s^-1\n    Peak rate:\t   1.49 +/- 0.24 ct s^-1\n    Peak flux:\t   (4.32 +/- 0.70)e-11 erg cm^-2 s^-1\n    ECF:\t   2.91e-11 erg cm^-2 ct^-1, assuming NH=1.85e+21 cm^-2,\n\t\t   gamma=2.42; determined from a spectral fit.\n    This matches a catalogued X-ray source XMMSL3 J154404.2-331108\n    in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:\n      Separation:  3.0\" from the XRT source\n      Cat Rate:    5.9e-01 +/- 2.8e-01 ct s^-1 \n      Cat Flux:    4.6e-12 +/- 2.2e-12 erg cm^-2 s^-1 (0.3-10 keV)\n\t     so the source  is 5.2-sigma above the catalogued flux.\n    There is no evidence for fading.\n    A SIMBAD object `CD-32 11039B' is 3.3\" away.\n    There is 1 2MASS object within the source's 3-sigma error radius.\n\n\nWe have detected a total of 2 sources. These have been automatically classified as\nfollows:\n  * 0 likely counterparts\n  * 1 candidate counterpart\n  * 1 uncatalogued X-ray source\n  * 0 known X-ray sources\n\nUncatalogued X-ray sources\n--------------------------\n\n  Source 2 (SWIFT J154417.0-331013):\n  ==================================\n    RA (J2000.0):  236.0710  =\t15h 44m 17.04s\n    Dec (J2000.0): -33.1705  =\t-33d 10' 13.8\"\n    Error:\t   10.3 (arcsec, radius, 90% confidence).\n    Detect flag:   POOR\n    Distance:\t   2.5 arcmin from the Einstein Probe/WXT position.\n    Mean rate:\t   0.0122 [+0.0068, -0.0053] ct s^-1\n    Mean flux:\t   (1.56 [+0.87, -0.67])e-11 erg cm^-2 s^-1\n    Peak rate:\t   0.0122 [+0.0068, -0.0053] ct s^-1\n    Peak flux:\t   (1.56 [+0.87, -0.67])e-11 erg cm^-2 s^-1\n    ECF:\t   1.28e-09 erg cm^-2 ct^-1, assuming NH=3.49e+23 cm^-2,\n\t\t   gamma=9.92; determined from a spectral fit.\n    XMM UL:\t   1.8e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t so the source is 1.8-sigma above this 3-sigma upper limit.\n    There is no evidence for fading.\n    A SIMBAD object `UCAC4 285-083088' is 1.7\" away.\n    There are 10 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.\n\nThis circular is an officicial product of the Swift-XRT team.\n\n\n",
  "createdOn": 1750174892637,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "version": 2,
  "circularId": 40756,
  "eventId": "EP-WXT 01709178975",
  "subject": "EP#01709178975: Swift-XRT counterpart detection",
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>",
  "bibcode": "2025GCN.40756....1E",
  "editedOn": 1750176438397,
  "format": "text/plain",
  "submittedHow": "email"
}