TITLE: GCN CIRCULAR NUMBER: 39811 SUBJECT: EP250321a: Swift-XRT detection of an X-ray source DATE: 25/03/21 11:18:07 GMT FROM: K.L. Page at U Leicester klp5@leicester.ac.uk
K.L. Page, P.A. Evans (U.Leicester) and M.H. Siegel (PSU) report on behalf of the Swift-XRT Team:
On 2025 March 21 at 07:26 UT, Swift started observing EP250321a, 4.6 ks after the Einstein Probe trigger (GCN Circ. 39800). A previously-uncatalogued X-ray source was identified, at a position of RA, Dec = 179.26259, +17.3628, which is equivalent to
RA (J2000): 11h 57m 03.02s Dec (J2000): +17d 21' 46.1"
with an uncertainty of 2.6 arcsec (radius, 90% confidence). This is consistent with the position of the optical and NIR source reported (GCN Circs. 39804, 39805, 39807, 39809, 39810).
The first snapshot of data, spanning 4.6-6.2 ks after the trigger, shows some X-ray flaring, with a mean X-ray flux of 3.7 (+0.4, -0.4) x 10^-11 erg cm-2 s-1 (observed, 0.3-10 keV).
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