Radio Synchrotron Emission from the Bow Shock of G2

TL;DR

This paper models the radio synchrotron emission from G2's bow shock, predicting it to be faint if G2 is a stellar wind, contrasting with brighter emissions expected if G2 is a gas cloud, aiding in understanding G2's nature.

Contribution

It provides detailed calculations of radio emission from G2's bow shock under different models, offering a method to distinguish G2's true nature before periapsis.

Findings

Radio flux from stellar wind model is below Sgr A*'s quiescent flux.

Cloud model predicts detectable radio emission already observed.

Radio measurements can identify G2's nature before periapsis.

Abstract

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.