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GCN Circular 33465

Subject
GRB 230307A: Swift-XRT afterglow detection
Date
2023-03-13T11:21:46Z (a year ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU) and P.A. Evans (U.
Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has conducted further observations of the field of the
Fermi/GBM-detected burst GRB 230307A (Dalessi et al. GCN Circ. 33407).
The observations now extend from T0+83.6 ks to T0+437.2 ks. 

Of the sources reported by Burrows et al. (GCN Circ. 33429), "Source 2"
is fading with >3-sigma significance, and is therefore likely the GRB
afterglow. Using 1252 s of PC mode data and 1 UVOT image, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 60.85935, -75.37884
which is equivalent to:

RA (J2000): 04h 03m 26.24s
Dec(J2000): -75d 22' 43.8"

with an uncertainty of 3.2 arcsec (radius, 90% confidence). This
position is 13.3 arcsec from the IPN improved position (Kozyrev et al.
GCN Circ. 33461). 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.1 (+0.6, -0.5).

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021537.
The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00110.

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