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GCN Circular 6520

Subject
SWIFT J195509.6+261406 / GRB 070610: SWIFT continued observations
Date
2007-06-12T16:02:08Z (17 years ago)
From
Claudio Pagani at PSU/Swift-XRT <pagani@astro.psu.edu>
C. Pagani (PSU), C. B. Markwardt (CRESST/U.Md./GSFC), P. Evans (U. Leicester), 
F. Gavriil (NPP/GSFC), J. A. Kennea (PSU), A. D. Falcone (PSU), W. Landsman 
(NASA/GSFC) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift 
Team:

We report on the continued SWIFT observations of the BAT trigger 281993, 
originally designated GRB 070610.
 
We have collected 13.2 ks of XRT Photon Counting data in the T+3.1 ks to T+122 
ks time interval.  The X-ray light curve shows evidence of rapid variability, 
with intense flaring activity and a possible late rebrightening.
Unlike a typical GRB afterglow, the lightcurve has shown no evidence of 
overall fading.

We can exclude at this point a GRB afterglow origin of the counterpart 
observed by the narrow field instruments.  The BAT trigger 281993 is probably 
a Galactic X-ray Transient, but we can not completely discard the possibility 
of a GRB origin with an undetected X-ray counterpart.
In particular, an undetected afterglow from a short GRB (the T90 for 
this trigger is 4.6 sec, GCN Circ. 6491) would not be unusual considering the 
XRT observations started at T+3.1 ks.  The flaring behavior reported by 
ground based observations (GCN Circ. 6492, GCN Circ. 6501, GCN Circ. 6505, 
GCN Circ. 6508) also favors the fast X-ray transient origin of the 
counterpart. For additional details on the interpretations on the origin of 
the source, refer to Markwardt et al. ATEL #1102.

The X-ray spectrum of the PC data in the T+3.1 ks to T+122 ks time interval, 
modeled with an absorbed power law, gives a photon index of 1.8+/-0.3 with the 
total column density consistent with the Galactic value of 1.01e22 cm**-2. 
The absorbed (unabsorbed) 0.3-10.0keV average flux in the T+3.1 ks - T+122 ks 
time interval is 2.4E-12 (3.9E-12) ergs cm^-2 s^-1.

We also note that in the XRT field of view we detect an additional X-ray 
source 4.3 arcmin from the BAT refined position (and outside of the BAT 1.8 
arcmin 90% error circle) that is most probably an X-ray active star.  The 
analysis of this source (designated SWIFT J195456.7+261301) will be reported 
in a separate ATEL.
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