# Radio Emission from Sgr A*: Pulsar Transits Through the Accretion Disc

## TL;DR

This paper proposes a model where a pulsar orbiting Sgr A* injects non-thermal particles into the accretion disc during transits, explaining observed radio emissions at GHz frequencies.

## Contribution

It introduces a novel mechanism involving pulsar transits to produce non-thermal particles in the accretion flow around Sgr A*.

## Key findings

- Relativistic pairs are injected into the disc during pulsar transits.
- The model produces steady synchrotron emission matching observed GHz luminosities.
- Periodic pulsar transits can sustain the observed radio emission levels.

## Abstract

Radiatively inefficient accretion flow models have been shown to accurately account for the spectrum and luminosity observed from Sgr A* in the X-ray regime down to mm wavelengths. However, observations at a few GHz cannot be explained by thermal electrons alone but require the presence of an additional non-thermal particle population. Here, we propose a model for the origin of such a population in the accretion flow via means of a pulsar orbiting the supermassive black hole in our Galaxy. Interactions between the relativistic pulsar wind with the disc lead to the formation of a bow shock in the wind. During the pulsar's transit through the accretion disc, relativistic pairs, accelerated at the shock front, are injected into the disc. The radio-emitting particles are long-lived and remain within the disc long after the pulsar's transit. Periodic pulsar transits through the disc result in regular injection episodes of non-thermal particles. We show that for a pulsar with spin-down luminosity $L_{\rm sd} \sim 3\times 10^{35}$ erg s$^{-1}$ and a wind Lorentz factor of $\gamma_{\rm w} \sim 10^4$ a quasi-steady synchrotron emission is established with luminosities in the $1-10$ GHz range comparable to the observed one.