GCN Circular 39584
Subject
EP250304a: Swift-XRT detection of a fading X-ray source
Date
2025-03-04T09:18:19Z (11 days ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
K.L. Page, P.A. Evans (U.Leicester) and J. DeLaunay (PSU) report on
behalf of the Swift XRT Team:
On 2025 March 04 at 02:59 UT, Swift started observing EP250304a, 5.2 ks
after the Einstein Probe trigger (GCN Circ. 39580). A fading X-ray source
was identified, at a position of RA, Dec = 208.39408, -42.8046, which is
equivalent to
RA (J2000): 13h 53m 34.58s
Dec (J2000): -42d 48′ 16.7″
with an uncertainty of 4.1 arcsec (radius, 90% confidence). This
is consistent with the FXT position (GCN Circ. 39580), as well as
the TRT optical counterpart given in GCN Circ. 39583.
The mean observed X-ray flux in the first snapshot was (3.5 +/- 0.4) x
10^-12 erg cm^-2 s^-1 (0.3 - 10 keV). By the time of the second snapshot,
at 10.3 ks after the trigger, the source was no longer detected, having
faded to a 3-sigma upper limit of 2.1 x 10^-12 erg cm^-2 s^-1.