GCN Circular 29449

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
Not found
 
 
), 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
Not found
 
 
).

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.