TITLE:   GCN CIRCULAR
NUMBER:  15683
SUBJECT: GRB 131209A: Further Swift XRT  observations 
DATE:    14/01/05 03:06:33 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <dxg35@psu.edu>

Dirk Grupe (Swift MOC, PSU)  reports on behalf of the 
Swift team:

We report on further Swift XRT observations of the field of the 
FERMI/LAT-discovered GRB 131209A (Vianello et al., GCN circ. 
15587). As reported in GCN circular 15592 (Grupe & Breeveld) 
there was one uncatalogued X-ray source found within the IPN error
box reported by Hurley et al. (GCN circ. 15588). We followed this
source  with Swift on 2013-December 17. This observation 
suggested a decaying source with a decay slope of about 1. 
Although this is a rather flat decay slope during the normal decay 
phase of a GRB X-ray afterglow, it is not uncommon (e.g. Grupe et 
al. 2013, ApJS, 209, 20). Nevertheless, it is also consistent with
a variability by a factor of 2.5 which is quite common for an AGN
(e.g. Grupe et al. 2010, ApJS, 187, 64). Therefore the data were
not conclusive. We therefore performed two additional observations
which were performed on 2014-January 02 and 03. During the
2014-January 02 observation the source had brightened again to a
count rate in the XRT of (6.4+2.2-1.7)e-3 counts s^-1 and then 
dropped again down to (1.8+1.1-0.8)e-3 counts s^-1 during the
January 03 observation. These observations suggest that the
uncatalogued source in the IPN error box is not the X-ray
afterglow of GRB 131209A. The rapid X-ray variability may suggest
that this is either a Narrow Line Seyfert 1 Galaxy or a blazar if
this is a background AGN. 


This report is an official product of the Swift team.