Limits on Simultaneous and Delayed Optical Emission from Well-localized Fast Radio Bursts

Abstract

We present the largest compilation to date of optical observations during and following fast radio bursts (FRBs). The data set includes our dedicated simultaneous and follow-up observations, as well as serendipitous archival survey observations, for a sample of 15 well-localized FRBs: eight repeating and seven one-off sources. Our simultaneous (and nearly simultaneous with a 0.4 s delay) optical observations of 13 (1) bursts from the repeating FRB 20220912A provide the deepest such limits to date for any extragalactic FRB, reaching a luminosity limit of ν L ν ≲ 1042 erg s−1 (≲2 × 1041 erg s−1) with 15–400 s exposures; an optical-flux-to-radio-fluence ratio of f opt/F radio ≲ 10−7 ms−1 (≲10−8 ms−1); and a flux ratio of f opt/f radio ≲ 0.02–≲2 × 10−5 (≲10−6) on millisecond to second timescales. These simultaneous limits provide useful constraints in the context of FRB emission models, such as the pulsar magnetosphere and pulsar nebula models. Interpreting all available optical limits in the context of the synchrotron maser model, we find that they constrain the flare energies to ≲1043–1049 erg (depending on the distances of the various repeating FRBs, with ≲1039 erg for the Galactic SGR 1935+2154). These limits are generally at least an order of magnitude larger than those inferred from the FRBs themselves, although in the case of FRB 20220912A our simultaneous and rapid follow-up observations severely restrict the model parameter space. We conclude by exploring the potential of future simultaneous and rapid-response observations with large optical telescopes.

Limits on Optical Counterparts to the Repeating Fast Radio Burst 20180916B from High-speed Imaging with Gemini-North/‘Alopeke

“…It remains open whether FRB 20180916B is representative of the known FRB population or if there can be multiple progenitor and emission channels with a variety of optical-to-radio fluence ratios. Hiramatsu et al (2023) found that targeted follow-up within 3 days of a new burst from a repeating FRB yielded observations coincident with a subsequent burst ≈40% of the time. As opposed to our strategy of targeting the periodic FRB 20180916B near the peak of its expected activity period, this strategy makes it possible to obtain new optical burst detections across a variety of sources and deeper luminosity limits for those at closer distances (e.g., the repeating FRB in the globular cluster of M81 at 3.6 Mpc, FRB 20200120E; Kirsten et al 2022).…”

“…Another potential local analog to FRB progenitors is the Galactic magnetar SGR 1935+2154, from which FRB-like pulses have been observed (Bochenek et al 2020b;CHIME/ FRB Collaboration et al 2020). Located in the Galactic center, it is severely affected by dust extinction, and thus despite some efforts to observe their putative optical and infrared counterparts, these have been unsuccessful (e.g., De et al 2020;Zampieri et al 2022;Hiramatsu et al 2023). However, some of these radio pulses have presented simultaneous X-ray emission (Mereghetti et al 2020;Ridnaia et al 2021;Tavani et al 2021).…”

“…This model has been explored in detail in the literature (Lyubarsky 2014;Beloborodov 2017;Waxman 2017;Lu & Kumar 2018;Metzger et al 2019;Margalit et al 2020). It is a promising model for optical counterparts, because some emission mechanisms predict a longer-lived afterglow that can in principle be detected by untargeted surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time (Yang et al 2019), or the targeted follow-up of FRBs (Kilpatrick et al 2021;Hiramatsu et al 2023;Trudu et al 2023). Given the timescale of our observations, we consider a prompt optical counterpart with a millisecond timescale, which in general will have a fluence ≈2 × 10 −6 times that of the radio (Yang et al 2019).…”