GCN Circular 40528
Subject
EP#01709176612: Swift-XRT counterpart detection of flaring star
Date
2025-05-22T19:17:02Z (a day ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), M. Capalbi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), P. D'Avanzo
(INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A.
Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri
(SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti
(INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected
source EP#01709176612, collecting 2.0 ks of Photon Counting (PC) mode data between
T0+4.2 ks and T0+9.7 ks after the trigger. A candidate counterpart has been found.
The details of this source are:
Source 1 (SWIFT J122501.5-521613):
==================================
RA (J2000.0): 186.2566 = 12h 25m 01.58s
Dec (J2000.0): -52.2705 = -52d 16' 13.8"
Error: 3.5 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 23 arcsec from the Einstein Probe/WXT position.
Mean rate: 2.883 +/- 0.078 ct s^-1
Mean flux: (9.45 +/- 0.26)e-11 erg cm^-2 s^-1
Peak rate: 5.3 +/- 1.1 ct s^-1
Peak flux: (1.74 +/- 0.37)e-10 erg cm^-2 s^-1
ECF: 3.28e-11 erg cm^-2 ct^-1, assuming NH=2.18e+21 cm^-2,
gamma=2.19; determined from a spectral fit.
This matches a catalogued X-ray source XMMSL3 J122501.2-521616
in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:
Separation: 2.9" from the XRT source
Cat Rate: 6.3e-01 +/- 2.6e-01 ct s^-1
Cat Flux: 5.5e-12 +/- 2.3e-12 erg cm^-2 s^-1 (0.3-10 keV)
so the source is 4.5-sigma above the catalogued flux.
The source may be fading, at the 1.0-sigma level.
A SIMBAD object `WISEA J122501.45-521614.6' is 1.5" away.
There are 2 2MASS objects within the source's 3-sigma error radius.
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
This is most likely a stellar flare of a Young Stellar Object Candidate Gaia DR3
6077506855610363648 (GCN 40523, Song et al.)
The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/EP.
This circular is an officicial product of the Swift-XRT team.