GCN Circular 40163
Subject
EP20250416a: Swift/XRT counterpart detection
Date
2025-04-17T15:06:58Z (8 months ago)
From
Tullia Sbarrato at INAF-OAB <tullia.sbarrato@inaf.it>
Via
Web form
T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team:
Swift-XRT has performed follow-up observations of EP/WXT-detected transient EP 250416a (Zhao et al., GCN 40154). We searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode data, from T0+17.1 ks to T0+23.2 ks after the EP/WXT trigger.
An uncatalogued X-ray source is detected within the estimated 3-sigma EP/WXT error region.
Using 2000 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 256.41935, +25.7751 which is equivalent to:
RA (J2000): 17h 05m 40.64s
Dec(J2000): +25d 46’ 30.4"
with an uncertainty of 3.1 arcsec (radius, 90% confidence). This position is 1 arcmin from the EP/WXT position, and consistent with the optical candidate reported by Levan et al., (GCN 40160).
The source has a mean count rate of 9.9e-02 ct/sec and currently shows no signs of fading.
The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00034/
This circular is an official product of the Swift-XRT team.