# How bright are fast optical bursts associated with fast radio bursts?

## TL;DR

This paper assesses the likelihood of detecting fast optical bursts associated with FRBs, concluding that detection is unlikely unless extreme conditions are present, but such detections could reveal critical environmental insights.

## Contribution

It explores the potential brightness of FOBs via inverse Compton processes and evaluates the detectability under various extreme astrophysical conditions.

## Key findings

- Detectable FOBs require very special conditions in FRB environments.
- Most electrons must have finely tuned energy distributions for optical IC emission.
- Detection prospects are low unless extreme magnetic fields or young SNRs are involved.

## Abstract

The origin of fast radio bursts (FRBs) is still unknown. Multi-wavelength observations during or shortly after the FRB phase would be essential to identify the counterpart of an FRB and to constrain its progenitor and environment. In this work, we investigate the brightness of the "fast optical bursts" (FOBs) associated with FRBs and the prospects of detecting them. We investigate several inverse Compton (IC) scattering processes that might produce an FOB, including both the one-zone and two-zone models. We also investigate the extension of the same mechanism of FRB emission to the optical band. We find that a detectable FOB with the current and forthcoming telescopes is possible under the IC scenarios with very special conditions. In particular, the FRB environment would need to invoke a neutron star with an extremely strong magnetic field and an extremely fast spin, or an extremely young supernova remnant (SNR) surrounding the FRB source. Furthermore, most electrons in the source are also required to have a fine-tuned energy distribution such that most of the IC energy is channeled in the optical band. We conclude that the prospect of detecting FOBs associated with FRBs is low. On the other hand, if FOBs are detected from a small fraction of FRBs, these FOBs would reveal extreme physical conditions in the FRB environments.