{
  "bibcode": "2025GCN.40204....1S",
  "circularId": 40204,
  "body": "C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M.\nFerro (INAF-OAB), K. Page (U. Leicester), D. Malesani (DAWN/NBI and\nRadboud) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team:\n\nSwift/XRT has performed follow-up observations of EP-WXT detected transient\nEP250421a (trigger 01709135179, Zhao et al. GCN 40198).\nWe searched for X-ray sources in 1.8 ks of Photon Counting (PC) mode data,\nfrom T0+5.8 ks to T0+11.7 ks after the EP-WXT trigger.\nWe found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT\nerror region. Using 1772 s of XRT PC mode data and 2 UVOT images, we find\nan enhanced XRT position: RA, Dec = 172.420,-24.67568 which is equivalent\nto:\n\nRA (J2000): 11h 29m 40.80s\nDec (J2000): -24° 40' 32.4\"\n\nwith an uncertainty of 2.7 arcsec (radius, 90% confidence).\nThis position is 35 arcsec from the EP-WXT position, and consistent with\nthe X-ray counterpart found in EP/FXT data (Zhao et al., GCN 40198) and\nwith the optical counterpart reported by Lee et al. (GCN 40192), Fu et al.\n(GCN 40193), Liu et al. (GCN 40197).\n\nThe source has a mean count rate of 0.272 ct/s and shows signs of fading at\n2.8 sigma significance.\n\nThe results of the XRT-team automatic analysis are available at\nhttps://www.swift.ac.uk/EP/EP_FIELD00035/\n\nThis circular is an official product of the Swift-XRT team.\n",
  "submittedHow": "email",
  "submitter": "Chiara Salvaggio at INAF OABrera <chiara.salvaggio@inaf.it>",
  "createdOn": 1745312671022,
  "eventId": "EP250421a",
  "subject": "EP250421a: Swift/XRT counterpart detection"
}