Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 23474

GRB 181201A: Swift-XRT afterglow detection
2018-12-01T14:17:02Z (5 years ago)
Kim Page at U.of Leicester <>
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia
(ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), S. J. LaPorte
(PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU) and P.A. Evans
(U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the INTEGRAL-detected
burst GRB 181201A (Mereghetti et al. GCN Circ. 23469), collecting 5.0
ks of Photon Counting (PC) mode data between T0+14.3 ks and T0+26.4 ks.

Five uncatalogued X-ray sources are detected, of which one ("Source 5")
is above the RASS limit, and is therefore likely the GRB afterglow.
Using 4968 s of PC mode data and 3 UVOT images, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 319.29666, -12.63082 which is
equivalent to:

RA (J2000): 21h 17m 11.20s
Dec(J2000): -12d 37' 51.0"

with an uncertainty of 2.0 arcsec (radius, 90% confidence). This
position is 28 arcsec from the INTEGRAL position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.44 (+/-0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.74 (+0.08, -0.07). The
best-fitting absorption column is  6.1 (+2.0, -0.9) x 10^20 cm^-2,
consistent with the Galactic value of 5.2 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 3.8 x 10^-11 (4.2 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.1 (+2.0, -0.9) x 10^20 cm^-2
Galactic foreground: 5.2 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.74 (+0.08, -0.07)

If the light curve continues to decay with a power-law decay index of
1.44, the count rate at T+24 hours will be 0.30 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-11 (1.3 x 10^-11) erg cm^-2 s^-1.

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

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