TITLE: GCN CIRCULAR NUMBER: 33556 SUBJECT: GRB 230328B: Swift/UVOT Detection DATE: 23/04/02 23:10:18 GMT FROM: Mike Siegel at PSU/Swift MOC mhs18@psu.edu
M. H. Siegel (PSU) and J. D. Gropp (PSU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 230328B 114 s after the BAT trigger (Gropp et al., GCN Circ. 33527). A source consistent with the XRT position (Osborne et al. GCN Circ. 33529) is detected in the initial UVOT exposures, confirming the initial optical detections (Pankov et al., GCN Circ. 33528; Catapano & Izzo, GCN Circ. 33535; Suresh et al., GCN Circ. 33536; Adami et al., GCN Circ. 33537; Komesh et al., GCN Circ. 33539).
The preliminary UVOT position is: RA (J2000) = 19:24:01.88 = 291.00783 (deg.) Dec (J2000) = +80:00:34.6 = 80.00962 (deg.) with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white (fc) 114 264 147 18.38 +/- 0.05 White 5537 5735 196 20.16 +/- 0.14 white 28147 28879 713 21.88 +/- 0.32 v 655 849 39 >17.6 b 582 774 39 >18.3 u (fc) 326 576 246 19.20 +/- 0.16 w1 705 725 19 >18.5 w2 805 825 19 >18.0
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.070 in the direction of the burst (Schlegel et al. 1998).