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
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.