TITLE: GCN CIRCULAR NUMBER: 40574 SUBJECT: GRB 250527C: Swift/UVOT Upper Limits DATE: 25/05/29 21:29:30 GMT FROM: noelklin@umbc.edu
N. Klingler (UMBC / NASA-GSFC / CRESST II) reports on behalf of the Swift/UVOT team:
Swift/UVOT has performed observations of GRB 250527C centered on the BAT position, RA, Dec = 21h 18m 31.92s, +52d 44' 13.2" (= 319.633, 52.737 deg; 90% uncertainty of 5 arcmin) (DeLaunay et al.; GCN 40563). UVOT collected 4536 s of data between 96 ks and 113 ks post-trigger, using the White filter.
No uncatalogued/transient sources are detected, with an approximate 3 sigma upper limit > 22.56 (AB) in the 90% BAT localization region.
For the X-ray sources detected by XRT (https://www.swift.ac.uk/ToO_GRBs/00021843/): sources 3, 4, and 6 fall outside the UVOT field of view. XRT source 2 is not detected. XRT source 1 is a star: TYC 3953-1190-2. XRT 5 has an optical counterpart (AB mag 17.99 +/- 0.07), but it is seen in archival DSS images and thus does not appear to be a transient.
No correction has been made for the expected Galactic extinction due to the reddening of E(B-V) = 3.43 in the direction of the burst (Schlegel et al. 1998).
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