[vsnet-grb-info 14699] GRB 140320B: Swift-XRT detection of the afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16013
SUBJECT: GRB 140320B: Swift-XRT detection of the afterglow
DATE:    14/03/20 21:57:31 GMT
FROM:    Claudio Pagani at U of Leicester  <cp232 at star.le.ac.uk>

C. Pagani, K.L. Page, R.L.C. Starling, (U. Leicester) report on behalf 
of the Swift-XRT team:

We have analysed 4 ks of XRT data for the INTEGRAL detected GRB 140320B 
(Mereghetti et al. GCN Circ. 16004), from 11.6 s to 23.1 ks after the 
trigger. The data are entirely in Photon Counting (PC) mode. An 
uncatalogued, fading X-ray source is detected inside the INTEGRAL error 
circle.

Using 3683 s of XRT PC data and 4 UVOT images, we find an 
astrometrically corrected X-ray position (using the XRT-UVOT alignment 
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 
145.55932, 60.26822 which is equivalent to:

RA (J2000):  09 42 14.24
Dec (J2000): +60 16 05.6

with an uncertainty of 1.7 arcsec (radius, 90% confidence). This is 
consistent with the optical position reported by Guidorzi et al. (GCN 
16003) and Elenin et al. (GCN 16005).

The light curve can be modelled with a power-law decay with an index of 
alpha=1.12 (+1.21, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 2.3 (+0.4, -0.3). The 
best-fitting absorption column is  6 (+8, -6) x 10^20 cm^-2, consistent 
with the Galactic value of 2.4 x 10^20 cm^-2 (Kalberla et al. 2005). The 
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor 
deduced from this spectrum  is 2.8 x 10^-11 (3.0 x 10^-11) erg cm^-2 
count^-1.

If the light curve continues to decay with a power-law decay index of 
1.12, the count rate at T+24 hours will be 7.8 x 10^-3 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x 
10^-14 (2.3 x 10^-14) erg cm^-2 s^-1.

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