[vsnet-grb-info 28488] GRB 210802A: Swift-XRT afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30591
SUBJECT: GRB 210802A: Swift-XRT afterglow detection
DATE:    21/08/03 19:23:02 GMT
FROM:    Valerio D'Elia at ASDC  <valerio.delia at ssdc.asi.it>

B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , D.N. Burrows (PSU), J. D. Gropp (PSU) and P.A.
Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 210802A (Longo et al. GCN Circ. 30589) in
a series of observations tiled on the sky. The total exposure time is
5.2 ks, distributed over 4 tiles; the maximum exposure at a single sky
location was 2.3 ks. The data were collected between T0+41.7 ks and
T0+43.0 ks, and are entirely in Photon Counting (PC) mode. 

Twenty-eight uncatalogued X-ray sources are detected. Many of these
sources are in the bottom tile (likely a high background effect), and
in the left tile (possibly an extended emission related to a nearby
cluster of galaxies). One of the most significant sources ("Source 7")
is above the 2SXPS 3-sigma upper limit at this position, and is
therefore likely the GRB afterglow. Using 1246 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 = 230.72285, +29.90180 which is equivalent to:

RA (J2000): 15h 22m 53.48s
Dec(J2000): +29d 54' 06.5"

with an uncertainty of 3.5 arcsec (radius, 90% confidence). This
position is 9.8 arcmin from the Fermi/LAT position.  While we cannot
determine at the present time whether the source is fading, we note
that a previous 1 ks Swift-XRT visit of the field showed no sign of
Source 7 (https://www.swift.ac.uk/2SXPS/Fields/10000004351).

The results of the XRT-team automatic analysis of the likely afterglow
are at https://www.swift.ac.uk/xrt_products/TILED_GRB00100/Source7.php.

The results of the full analysis of the tiled XRT observations are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00100.

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