[vsnet-grb-info 28255] GRB 210702A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30358
SUBJECT: GRB 210702A: Swift-XRT refined Analysis
DATE:    21/07/03 08:49:45 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A.
Melandri (INAF-OAB) and A.Y. Lien report on behalf of the Swift-XRT
team:

We have analysed 6.3 ks of XRT data for GRB 210702A (Lien et al. GCN
Circ. 30351), from 84 s to 38.4 ks after the  BAT trigger. The data
comprise 310 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 4559 s of PC mode data and 10 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 = 168.57877, -36.74715
which is equivalent to:

RA (J2000): 11h 14m 18.91s
Dec(J2000): -36d 44' 49.7"

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=1.005 (+0.014, -0.013), followed by a break at T+7161 s
to an alpha of 1.68 (+0.11, -0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.570 (+0.018, -0.015). The
best-fitting absorption column is  consistent with the Galactic value
of 1.2 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.95 (+/-0.07) and a best-fitting absorption column
of 1.8 (+/-1.0) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.5 x
10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.2 x 10^21 cm^-2
Intrinsic column:    1.8 (+/-1.0) x 10^21 cm^-2 at z=1.16
Photon index:	     1.95 (+/-0.07)

If the light curve continues to decay with a power-law decay index of
1.68, the count rate at T+24 hours will be 0.044 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-12 (2.0 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01058804.

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