[vsnet-grb-info 27346] GRB 210209A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29449
SUBJECT: GRB 210209A: Swift-XRT refined Analysis
DATE:    21/02/10 08:13:33 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai
(INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea
(PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P.
Osborne (U. Leicester) and S. Laha report on behalf of the Swift-XRT
team:

We have analysed 6.3 ks of XRT data for GRB 210209A (Laha et al. GCN
Circ. 29442), from 122 s to 24.0 ks after the  BAT trigger. The data
comprise 139 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 29443).

The late-time light curve (from T0+4.3 ks) can be modelled with a
power-law decay with a decay index of alpha=0.88 (+/-0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.81 (+0.07, -0.04). The
best-fitting absorption column is  consistent with the Galactic value
of 3.7 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.91 (+0.07, -0.05) and a best-fitting absorption
column consistent with the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.0 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.67 (+0.14, -0.00) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.91 (+0.07, -0.05)

If the light curve continues to decay with a power-law decay index of
0.88, the count rate at T+24 hours will be 0.046 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x
10^-12 (2.6 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/01031636.

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