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GCN Circular 24919

Subject
GRB 190630B: Swift-XRT refined Analysis
Date
2019-06-30T17:37:06Z (5 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
K.L. Page (U. Leicester), P.A. Evans (U. Leicester) and F.E. Marshall
(NASA/GSFC) report on behalf of the Swift-XRT team:

We have analysed 2.4 ks of XRT data for GRB 190630B, from 47 s to 28.2
ks after the  BAT trigger. The data comprise 8 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. Using 307 s of PC mode data and 1 UVOT image, we
find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
223.70024, +41.52614 which is equivalent to:

RA (J2000): 14h 54m 48.06s
Dec(J2000): +41d 31' 34.1"

with an uncertainty of 3.1 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.32 (+0.08, -0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.0 (+1.1, -0.4). The
best-fitting absorption column is  consistent with the Galactic value
of 1.4 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 (3.3 x 10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1 (+/-20) x 10^20 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     3.0 (+1.1, -0.4)

If the light curve continues to decay with a power-law decay index of
1.32, the count rate at T+24 hours will be 6.5 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x
10^-14 (2.1 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00912102.

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