Title: A search for optical bursts from the repeating fast radio burst FRB 121102,
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.