GCN Circular 18448.5
Subject
GRB 151022A: Swift-XRT refined Analysis
Date
2015-10-23T02:22:04Z (9 years ago)
Edited On
2024-03-27T19:59:02Z (a month ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>
S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), B.
Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU)
and P. D'Avanzo report on behalf of the Swift-XRT team:
We have analysed 6.4 ks of XRT data for GRB 151022A (D'Avanzo et al.
GCN Circ. 18436), from 286 s to 31.4 ks after the BAT trigger. The
data comprise 17 s in Windowed Timing (WT) mode (the first 7 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. The enhanced XRT position for this burst was given by
Beardmore et al. (GCN Circ. 18438).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.82 (+0.17, -0.14).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.39 (+0.26, -0.24). The
best-fitting absorption column is 6.2 (+2.6, -1.5) x 10^21 cm^-2,
consistent with the Galactic value of 4.7 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 6.1 x 10^-11 (7.7 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 6.2 (+2.6, -1.5) x 10^21 cm^-2
Galactic foreground: 4.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.39 (+0.26, -0.24)
If the light curve continues to decay with a power-law decay index of
1.82, the count rate at T+24 hours will be 7.2 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.4 x
10^-15 (5.5 x 10^-15) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00661036.
This circular is an official product of the Swift-XRT team.
[GCN OPS NOTE(15Jun16): Because of a processing error, two circulars
received the same ID Number. The second was given an "a' suffix.]
GCN OPS NOTE: The new GCN database requires the GCN Circular ID to be a number. Therefore, the previous GCN number assigned as 18448a was modified to 18448.5 during the GCN Circulars migration in April 2023.