GCN Circular 41491
Subject
EP250821a: Swift/UVOT further observations.
Event
Date
2025-08-22T09:44:34Z (2 days ago)
From
Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>
Via
email
S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on
behalf of the Swift-XRT and Swift-UVOT team:
Swift/UVOT has performed further follow-up observations of the Einstein
Probe/WXT-detected source EP250821a (Hu et al., GCN 41459). The UVOT optical
counterpart reported in (Dichiara et al., GCN 41469) has faded, consistent
with the behaviour reported by Li et al. (GCN 41470) and Yao et al. (GCN 41485).
The refined UVOT position is
RA (J2000) 19:19:32.56
Dec (J2000) -43:22:52.3
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). We note that
this position supersedes that reported in Dichiara et al. (GCN 41469), which
is incorrect. We apologise for any confusion.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL
v 61584 72904 799 >19.9
u 5186 11029 1897 18.88+\-0.08 (reported in GCN 41469)
u 68377 68575 195 >19.8
uvw1 67966 68372 399 >20.0
uvm2 67555 67961 399 >19.8
uvw2 61180 72857 1168 >20.2
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.07 in the direction of the burst
(Schlegel et al. 1998).