[vsnet-grb-info 26241] GRB 200901A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28341
SUBJECT: GRB 200901A: Swift-XRT refined Analysis
DATE:    20/09/01 18:09:03 GMT
FROM:    Boris Sbarufatti at PSU  <bxs60 at psu.edu>

J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , A. Tohuvavohu (U. Toronto), B. Sbarufatti
(PSU) and K. K. Simpson (PSU) report on behalf of the Swift-XRT team:

We have analysed 2.5 ks of XRT data for GRB 200901A (Simpson et al. GCN
Circ. 28335), from 3.1 ks to 11.1 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. Using 1707 s of PC mode data
and 4 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 = 61.78319, -59.89084 which is equivalent to:

RA (J2000): 04h 07m 07.97s
Dec(J2000): -59d 53' 27.0"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.95 (+0.28, -0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.31 (+0.30, -0.28). The
best-fitting absorption column is  2.2 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 x 10^20 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 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: 4.2 sigma
Photon index:	     2.31 (+0.30, -0.28)

If the light curve continues to decay with a power-law decay index of
0.95, the count rate at T+24 hours will be 7.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-13 (3.8 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00994143.

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