[vsnet-grb-info 13892] GRB 130828A: Further Swift XRT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15206
SUBJECT: GRB 130828A: Further Swift XRT observations  
DATE:    13/09/09 21:13:13 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <dxg35 at psu.edu>

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

We report on two follow-up observations of the field of GRB 130828A
which was discovered by the FERMI LAT as reported by Vianello & 
Sonbas (GCN circ 15128). The first Swift observation was performed 
on 2013-09-04 (obsID 20293) for 2.6ks and was centered on the 
X-ray source reported in Grupe et al. (GCN circ. 15135). This X-ray
source is still present in the new observation suggesting that 
these X-rays are emitted from the Seyfert 1.9 galaxy 
SDSS J171855.44+275947.4 as suggested by Grupe et al. Support
for this assumption comes from new IPN measurements by 
Hurley et al. (GCN circ. 15138) who published a new IPN error box. 
The X-ray source associated with SDSS J171855.44+275947.4 is 
significantly outside this error box.

We re-examined the Swift observation of the field which contains 
the IPN error box (obsID 20289) and found enhanced X-ray emission 
within the IPN error  box reported by Hurley et al. Applying the 
Bayesian statistics as  described by Kraft et al. (1991, ApJ, 374, 
344) suggesting a source  detection at the 3sigma level of 
(2.4+4.2-2.1)e-3 counts/s. The position of this marginally 
detected source is:

RA(hh mm ss.s) = 17h19m09.24s
Dec(dd mm ss.s) = +28:13:14.05

with an uncertainty of 8".

We re-observed the position of this source with Swift on 2013-09-07 
for a total of 5157s (obsID 20295). No source was detected in this
observation. The 3sigma upper limit at the position of the 
previously detected X-ray source within the IPN error box is 
1.3e-3 counts/s. This may suggest that the X-ray source found 
within the IPN error box during observation 20289 is the X-ray 
afterglow of GRB 130828A. Note, however, that considering the
3sigma errors given above, this upper limit is non-conclusive. 

No further Swift  observations are planned of this GRB.

This circular is an official product of the Swift team.