GCN Circular 43271
Subject
GRB 251230A: Swift/UVOT detection
Event
Date
2025-12-30T13:45:04Z (2 days ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL), N.P.M. Kuin (UCL-MSSL), S. Lanava (PSU) and M. De Pasquale (U. Messina) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251230A 76s after the BAT trigger (Lanava et al., GCN Circ. 43252).
A bright, fading source consistent with the enhanced XRT position (Osborne et al., GCN Circ. 43263) and optical detections (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, He et al., GCN 43269) is detected in the initial UVOT exposures in the white, v, b, u and uvw1 filters.
The burst is also detected in the UV grism and, while there is some contamination from other zeroth orders, we obtain a tentative redshift of z=1.73.
The preliminary UVOT position is:
RA (J2000) = 11:59:35.41 = 179.89756 (deg.)
Dec (J2000) = +11:26:19.2 = 11.43867 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the finding chart (FC) and other early settled exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 76 226 147 13.61 ± 0.03
white 868 1017 286 15.63 ± 0.02
v 619 638 19 14.69 ± 0.07
b 545 564 20 14.78 ± 0.05
u_FC 288 538 246 13.77 ± 0.02
uvw1 668 687 19 15.2 ± 0.1
uvm2 643 1775 136 >18.8
uvw2 594 614 19 >17.7
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.024 in the direction of the burst (Schlegel et al. 1998).