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GCN Circular 27331

Subject
GRB 200306A: Swift-XRT refined Analysis
Date
2020-03-07T00:38:06Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (ASDC), B.
Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore
(U. Leicester) and K.K. Simpson report on behalf of the Swift-XRT team:

We have analysed 2.1 ks of XRT data for GRB 200306A (Simpson et al. GCN
Circ. 27320), from 66 s to 6.2 ks after the  BAT trigger. The data
comprise 186 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 2051 s of PC mode data and 6 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 = 101.10233, -62.00654
which is equivalent to:

RA (J2000): 06h 44m 24.56s
Dec(J2000): -62d 00' 23.5"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=4.05 (+/-0.21).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.93 (+/-0.14). The
best-fitting absorption column is  5.2 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 8.6 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.89 (+0.19, -0.18)
and a best-fitting absorption column of 4.3 (+1.1, -0.9) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.2 x 10^-11 (6.3 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.3 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 8.6 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     1.89 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
4.05, the count rate at T+24 hours will be 3.6 x 10^-11 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x
10^-21 (2.3 x 10^-21) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00959917.

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