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GCN Circular 6520

SWIFT J195509.6+261406 / GRB 070610: SWIFT continued observations
2007-06-12T16:02:08Z (17 years ago)
Claudio Pagani at PSU/Swift-XRT <>
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 

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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