GCN Circular 30416

D.N. Burrows (PSU), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), T. Sbarrato (INAF-OAB), P.
D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), J. D. Gropp (PSU) and
B. Sbarufatti report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 210708A (Sbarufatti et al.
GCN Circ. 30413
Not found
 
 
), from 85 s to 22.8 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The refined XRT position is
RA, Dec = 173.7372, -49.1515 which is equivalent to:

RA (J2000): 11 34 56.92
Dec(J2000): -49 09 05.4

with an uncertainty of 7.0 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.76 (+0.30, -0.65).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+0.4, -0.3). The
best-fitting absorption column is  3.0 (+1.2, -1.0) x 10^21 cm^-2, in
excess of the Galactic value of 1.6 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.0 x 10^-11 (5.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.0 (+1.2, -1.0) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: 2.2 sigma
Photon index:	     2.5 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
1.76, the count rate at T+24 hours will be 8.8 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x
10^-16 (5.1 x 10^-16) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01059460.

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