The type Ib supernova 2010O: an explosion in a Wolf-Rayet X-ray binary?
  The type Ib supernova 2010O was recently discovered in the interacting
starburst galaxy Arp 299. We present an analysis of two archival Chandra X-ray
observations of Arp 299, taken before the explosion and show that there is a
transient X-ray source at a position consistent with the supernova. Due to the
diffuse emission, the background is difficult to estimate. We estimate the flux
of the transient from the difference of the two X-ray images and conclude that
the transient can be described by a 0.225 keV black body with a luminosity of
2.5+/-0.7 10^{39} erg/s for a distance of 41 Mpc. These properties put the
transient in between the Galactic black hole binary XTE J1550-564 and the
ultra-luminous X-ray binaries NGC 1313 X-1 and X-2. The high level of X-ray
variability associated with the active starburst makes it impossible to rule
out a chance alignment. If the source is associated with the supernova, it
suggests SN2010O is the explosion of the second star in a Wolf-Rayet X-ray
binary, such as Cyg X-3, IC 10 X-1 and NGC 300 X-1.
