GCN Circular 15734

Dirk Grupe (Swift MOC, PSU) and Phil Evans (U Leicester) report
on behalf  of the  Swift team:

We report on further Swift XRT observations of the field of the
Fermi GBM and LAT detected GRB 140104B (Xiong, GCN Circ. 15687
Not found
 
 
, 
G. Vianello GCN Circ. 15684
Not found
 
 
, respectively). 
We detected an uncatalogued X-ray source in the first Swift 
observation of the field of GRB 140104B starting at 15.5 hours
after the Fermi trigger (Grupe, GCN circ 15691) at

Ra-2000  =  14 35 01.0
Dec-2000 = -09 01 40.7

with an uncertainty of 4.0". The XRT count rate of this source
was (8.1+/-1.6)e-3 counts s^-1. Note that we misidentified this
source in the previous circular (15691) with the star TYC
5564-19-1, which however, is 2.2' away from this X-ray position. 

We re-observed this source on 2014-01-14 for 4.6 ks again with
Swift (9.5 days after the trigger). We do not detect this source
in the XRT any more, suggesting that this may be the X-ray
afterglow of GRB 140104B. The 3sigma upper limit at the position
of this source is 1.3e-3 counts s^-1. Note, however, that this is
not conclusive. This source can still be a highly variable
background AGN (see e.g. Grupe et al. 2010, ApJS, 187, 64). 

If this source is the X-ray afterglow of GRB 140104B, the X-ray
spectrum appears to be rather soft. A spectral analysis of the
X-ray data shows that the X-ray photon index is Gamma =
2.7+/-0.68 which is rather steep (see Grupe et al. 2013, ApJS,
209, 20; Evans et al., 2009, MNRAS, 397, 1177). 
The absorption column density is consistent with the
Galactic value (5.63e20 cm^-2). This steep X-ray spectral index
and the steep energy spectral index and the high fluence in the
10-1000 keV band of the burst reported by Xiong (GCN circular 
15687
Not found
 
 
) suggests a low redshift nature of the burst (see Grupe et
al. 2013, ApJ, 209, 20).

However, the steep X-ray photon index of Gamma = 2.7
does not exclude a possible AGN nature of the source. In a 
matter of fact, if this is a background AGN then the steep X-ray 
spectrum suggest that this is most-likely a Narrow Line 
Seyfert 1 galaxy. This is also the type of AGN with the 
strongest X-ray variability  (e.g. Boller et al. 1996, 
Leighly 1999, Grupe et al. 2010). 



This report is an official product of the Swift team.