TITLE:   GCN CIRCULAR
NUMBER:  39967
SUBJECT: GRB 250328A: Swift-XRT refined Analysis
DATE:    25/03/31 09:33:00 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), M. A. Williams (PSU), S. Dichiara
(PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:

We have analysed 4.5 ks of XRT data for the SVOM/ECLAIRs-detected burst
GRB 250328A (SVOM trigger sb25032803), from 3.2 ks to 190.2 ks after
the  SVOM/ECLAIRs trigger. The data are entirely in Photon Counting
(PC) mode. We find an uncatalogued fading X-ray source. Using 1975 s of
PC mode data and 2 UVOT images, we find an enhanced XRT position (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 215.95979, +25.93224 which is equivalent to:

RA (J2000): 14h 23m 50.35s
Dec(J2000): +25d 55' 56.1"

with an uncertainty of 4.4 arcsec (radius, 90% confidence). This
position is 3.1 arcmin from the SVOM/ECLAIRs position and 1.6 arcsec
from the IR/optical afterglow candidate (Schneider et al., GCN 39919;
Schneider et al., GCN 39920; Li et al., GCN 39923; Li et al, GCN 39936;
Kumar et al., GCN 39946).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.67 (+0.24, -0.18).

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019661.

This circular is an official product of the Swift-XRT team.