A search for optical bursts from the repeating fast radio burst FRB 121102

TL;DR

This study searched for optical bursts associated with the repeating FRB 121102 using simultaneous optical and radio observations, finding no optical counterparts and setting upper limits on optical flux and spectral index.

Contribution

First simultaneous optical and radio observations of FRB 121102, establishing upper limits on optical emission and constraining spectral properties of the burst.

Findings

No optical bursts detected during radio bursts.

Set upper limit on optical flux density at 0.33 mJy.

Constrained spectral index to alpha < -0.2.

Abstract

We present a search for optical bursts from the repeating fast radio burst FRB 121102 using simultaneous observations with the high-speed optical camera ULTRASPEC on the 2.4-m Thai National Telescope and radio observations with the 100-m Effelsberg Radio Telescope. A total of 13 radio bursts were detected, but we found no evidence for corresponding optical bursts in our 70.7-ms frames. The 5-sigma upper limit to the optical flux density during our observations is 0.33 mJy at 767nm. This gives an upper limit for the optical burst fluence of 0.046 Jy ms, which constrains the broadband spectral index of the burst emission to alpha < -0.2. Two of the radio pulses are separated by just 34 ms, which may represent an upper limit on a possible underlying periodicity (a rotation period typical of pulsars), or these pulses may have come from a single emission window that is a small fraction of a possible period.