Skip to main content
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 22726

GRB 180514A: Swift-XRT refined Analysis
2018-05-14T21:07:55Z (6 years ago)
Phil Evans at U of Leicester <>
A. Tohuvavohu (PSU), Z. Liu (NAOC / U. Leicester), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), V. D'Elia (ASDC), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), S. J. LaPorte (PSU), J.A. Kennea
(PSU) and S.J. LaPorte report on behalf of the Swift-XRT team:

We have analysed 7.0 ks of XRT data for GRB 180514A (LaPorte et al. GCN
Circ. 22723), from 84 s to 18.0 ks after the  BAT trigger. The data
comprise 88 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Goad et al. (GCN Circ. 22725).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.4 (+0.5, -0.8). At T+135 s  the decay
steepens to an alpha of 4.9 (+1.0, -0.4) before breaking again at T+414
s to a final decay with index alpha=0.38 (+0.15, -0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.7 (+0.4, -0.3). The
best-fitting absorption column is  2.9 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 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 2.1 x 10^-11 (9.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     2.9 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 7.0 sigma
Photon index:	     3.7 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
0.38, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 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