[vsnet-grb-info 26015] GRB 200715A: Swift-XRT afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28115
SUBJECT: GRB 200715A: Swift-XRT afterglow detection
DATE:    20/07/16 08:44:31 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.
Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and P.A. Evans (U.
Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the INTEGRAL-detected
burst GRB 200715A (Mereghetti et al. GCN Circ. 28110), collecting 3.3
ks of Photon Counting (PC) mode data between T0+7.5 ks and T0+26.2 ks. 


An uncatalogued X-ray source is detected consistent with being within
266 arcsec of the INTEGRAL position and is above the RASS limit, and is
therefore likely the GRB afterglow.  The position of this source is RA,
Dec=248.5377, -51.8356 which is equivalent to:

RA (J2000): 16:34:9.04
Dec(J2000): -51:50:08.0

with an uncertainty of 3.7 arcsec (radius, 90% confidence).  This
position is 13 arcsec from the INTEGRAL position (Mereghetti et al. GCN
Circ. 28110). 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.06 (+0.32, -0.27).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.5). The
best-fitting absorption column is  1.06 (+0.60, -0.29) x 10^22 cm^-2,
consistent with the Galactic value of 7.6 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 4.8 x 10^-11 (9.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.06 (+0.60, -0.29) x 10^22 cm^-2
Galactic foreground: 7.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.1 (+/-0.5)

If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 6.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-13 (5.8 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/00021018.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021018.

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