Radio Synchrotron Emission from the Bow Shock of G2

The radio flux from the synchrotron emission of electrons accelerated in the forward bow shock of G2 is expected to peak when the forward shock passes pericenter, possibly 7 to 9 months before the center of mass of G2 reaches pericenter ~3x10^15 cm from the Galactic Center (Narayan et al. 2012; Sadowski et al. 2013a,b). In this letter, we calculate the radio emission from the forward and reverse shock if G2 is a momentum-supported bow shock of a faint star with a high mass-loss rate as suggested by Scoville & Burkert (2013); Ballone et al. (2013). We show that the radio flux lies well below the quiescent radio flux of Sgr A* and will be difficult to detect. By contrast, in the cloud model of G2, the radio flux of the forward shock is predicted to be much larger than the quiescent radio flux and therefore should have already been detected (Narayan et al. 2012; Sadowski et al. 2013b). Therefore, radio measurements can reveal the nature of G2 well before G2 completes its periapsis passage.