Skip to main content
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 17965

GRB 150626A: Swift-XRT refined Analysis
2015-06-26T14:32:33Z (9 years ago)
Phil Evans at U of Leicester <>
V. Mangano (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'ai
(INAF-IASFPA), A. Maselli  (INAF-IASFPA), M.C. Stroh (PSU), D.N.
Burrows (PSU) and T.G.R. Roegiers report on behalf of the Swift-XRT

We have analysed 9.2 ks of XRT data for GRB 150626A (Roegiers et al.
GCN Circ. 17960), from 77 s to 31.2 ks after the  BAT trigger. The data
comprise 206 s in Windowed Timing (WT) mode (the first 9 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 Evans et
al. (GCN Circ. 17961).

The late-time light curve (from T0+6.3 ks) can be modelled with a
power-law decay with a decay index of alpha=0.65 (+/-0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.08 (+/-0.06). The
best-fitting absorption column is  3.74 (+0.31, -0.24) x 10^21 cm^-2,
consistent with the Galactic value of 3.5 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 2.06 (+0.19,
-0.18) and a best-fitting absorption column of 4.5 (+1.0, -0.9) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.9 x 10^-11 (6.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.5 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 3.5 x 10^21 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.06 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
0.65, the count rate at T+24 hours will be 0.018 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x
10^-13 (1.1 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at

This circular is an official product of the Swift-XRT team.
Looking for U.S. government information and services? Visit