TITLE:   GCN CIRCULAR
NUMBER:  41491
SUBJECT: EP250821a: Swift/UVOT further observations.
DATE:    25/08/22 09:44:34 GMT
FROM:    Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>

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).