TITLE:   GCN CIRCULAR
NUMBER:  27704
SUBJECT: GRB 200509A: Swift-XRT refined Analysis
DATE:    20/05/09 18:28:52 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto),
B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB) and E. Troja report on behalf of the Swift-XRT
team:

We have analysed 9.4 ks of XRT data for GRB 200509A (Troja et al. GCN
Circ. 27701), from 104 s to 34.9 ks after the  BAT trigger. The data
comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Evans et al. (GCN Circ.
27703). The late-time light curve (from T0+5.0 ks) is consistent with a
constant source of mean count rate 1.8e-01 ct/sec. A power-law fit
gives an index of -0.2 (+/-1.2).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.725 (+/-0.020). The
best-fitting absorption column is  1.89 (+0.08, -0.07) x 10^21 cm^-2,
in excess of the Galactic value of 1.6 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.55 (+0.10, -0.08)
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 4.5 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.58 (+0.17, -0.00) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.55 (+0.10, -0.08)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00970886.

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