Radio Synchrotron Emission from a Bow Shock around the Gas Cloud G2 Heading toward the Galactic Center

TL;DR

This paper predicts that a gas cloud approaching the Galactic Center will create a bow shock that accelerates electrons, leading to detectable non-thermal radio emission that surpasses Sgr A*'s quiescent emission.

Contribution

It provides the first estimate of radio emission from a bow shock around G2, predicting observable signals during its pericenter passage.

Findings

Radio emission may exceed Sgr A*'s quiescent level by several times.

Enhanced emission should be detectable at GHz frequencies around pericenter.

The bow shock emission will be spatially displaced from Sgr A* by ~33 mas.

Abstract

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.