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 performed follow-up observations of the
Fermi/GBM-detected burst GRB 230307A (Dalessi et al. GCN Circ. 33407)
in a series of observations tiled on the sky. The total exposure time
is 8.6 ks, distributed over 32 tiles; the maximum exposure at a single
sky location was 1.6 ks. The data were collected between T0+76.4 ks and
T0+100.9 ks, and are entirely in Photon Counting (PC) mode.
Two X-ray sources have been detected within the improved IPN error box
(Kozyrev et al., GCN Circ. 33425), that has been fully covered by
RA (J2000): 04h 03m 26.24s = 60.85935��
Dec (J2000): -75�� 22��� 43.8��� = -75.3788��
Error: 3.4��� (radius, 90% conf., enhanced)
Count-rate: 0.019 (��0.004) ct s-1
Distance: 36.6 arcsec from IPN position
RA (J2000): 04h 03m 57.93s = 60.99137��
Dec (J2000): -75�� 21��� 26.8��� = -75.3574��
Error: 7.1��� (radius, 90% conf.)
Count-rate: 2.6 (+1.9, -1.3) ��10-3 ct s-1
Distance: 175 arcsec from IPN position
Source 2 is below the RASS limit and shows no definitive signs of
fading. Therefore, at the present time we cannot confirm this as the
afterglow. Source 3 is at a position consistent with a QSO candidate
(Wu et al., 2023, RAA, 23, 025006) and therefore is likely unrelated to
GRB 230307A. Further observations are ongoing.
The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00110.
This circular is an official product of the Swift-XRT team.