GCN Circular 38899
Subject
GRB 250109A / EP250109a: Swift detection of the X-ray afterglow
Date
2025-01-10T20:57:21Z (a month ago)
From
Jamie Kennea at Penn State <jak51@psu.edu>
Via
Web form
J. A. Kennea (PSU), P. A. Evans and K. L. Page (Leicester) report on behalf of the Swift/XRT team:
Swift/XRT performed a further 3.1ks of exposure on GRB 250109A (GCN #38887) AKA EP250109a (GCN #38864), following on from a rapid 1ks observation which did not detect the counterpart (GCN #38867). Combining the two datasets, we detect one point source inside the EP WXT error circle, at the following position: RA/Dec(J2000) = 88.80698, -12.4958, which is equivalent to:
RA(J2000) = 05h 55m 13.67s,
Dec(J2000) = -12° 29′ 44.8″,
with an estimated uncertainty of 5.8 arc-seconds radius (90% containment). This position lies 6 arc-seconds from the EP FXT position, and 1.1 arc-seconds from the SVOM-VT reported optical position (GCN #38872). Given the localization coincidence, this source is likely to be the afterglow of GRB 250109A.
The combined XRT flux from this afterglow is 9(+5,-4) x 10^-14 erg/s/cm^2 (0.3-10 keV).