{
  "circularId": 42401,
  "createdOn": 1761233742023,
  "bibcode": "2025GCN.42401....1E",
  "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#01709247298, collecting 1.6 ks of Photon Counting (PC) mode data between\nT0+6.6 ks and T0+8.3 ks after the trigger. A likely counterpart has been found. This\nsource is 43 arcmin from the position of the MAXI-detected transient GRB 251023B /\nMAXI J0451+122 (Kang et al., GCN Circ. 42392), well outside their error region, thus\nits association, while likely on temporal grounds, remains unconfirmed. The details\nof this source are:\n\n  Source 1 (SWIFT J045400.4+123929):\n  ==================================\n    RA (J2000.0):   73.5018  =\t04 54 00.43\n    Dec (J2000.0):  +12.6583  =  +12 39 29.9\n    Error:\t    3.7 (arcsec, radius, 90% confidence).\n    Detect flag:    GOOD\n    Distance:\t    22 arcsec from the Einstein Probe/WXT position.\n    Mean rate:\t    0.152 +/- 0.011 ct s^-1\n    Mean flux:\t    (5.94 +/- 0.44)e-12 erg cm^-2 s^-1\n    Peak rate:\t    0.221 +/- 0.049 ct s^-1\n    Peak flux:\t    (8.6 +/- 1.9)e-12 erg cm^-2 s^-1\n    ECF:\t    3.91e-11 erg cm^-2 ct^-1\n\t\t      assuming NH=3.15e+21 cm^-2, gamma=1.97\n\t\t      determined from a spectral fit.\n    XMM UL:\t    2.3e-12 erg cm^-2 s^-1, (0.3-10 keV)\n\t\t      so the source is 3.2-sigma above this 3-sigma upper limit.\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_FIELD00077.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "submittedHow": "email",
  "subject": "EP#01709247298: Swift-XRT counterpart detection"
}