Radio Synchrotron Emission from a Bow Shock around the Gas Cloud G2
  Heading toward the Galactic Center
  A dense ionized cloud of gas has been recently discovered to be moving
directly toward the supermassive black hole, Sgr A*, at the Galactic Center. In
June 2013, at the pericenter of its highly eccentric orbit, the cloud will be
approximately 3100 Schwarzschild radii from the black hole and will move
supersonically through the ambient hot gas with a velocity of v_p ~ 5400 km/s.
A bow shock is likely to form in front of the cloud and could accelerate
electrons to relativistic energies. We estimate via particle-in-cell
simulations the energy distribution of the accelerated electrons and show that
the non-thermal synchrotron emission from these electrons might exceed the
quiescent radio emission from Sgr A* by a factor of several. The enhanced radio
emission should be detectable at GHz and higher frequencies around the time of
pericentric passage and in the following months. The bow shock emission is
expected to be displaced from the quiescent radio emission of Sgr A* by ~33
mas. Interferometric observations could resolve potential changes in the radio
image of Sgr A* at wavelengths < 6 cm.
