![]() Although several astrophysical coherent emission mechanisms are identified with Galactic sources (Melrose 2017), these mechanisms encounter difficulties with the energy scales of FRBs. The high brightness temperatures (∼10 35 K) of FRBs require a coherent emission process. The exact FRB emission mechanism(s) and engine(s) remain elusive. 2020), indicating that at least some FRBs originate from noncatastrophic events (see also Ravi 2019). Repeat bursts have been observed from 20 FRB sources (Spitler et al. Five FRB sources have been directly associated with host galaxies, revealing a range of galaxy classes and source environments (Chatterjee et al. 2016), and the estimated rate is (Bhandari et al. ![]() There have been nearly a hundred FRBs reported (Petroff et al. Although our technique is robust to the present uncertainty in the FRB fluence distribution, its ultimate application to accurately estimate or bound η will require the careful analysis of all candidate fast transient events in multiwavelength survey data sets.įast radio bursts (FRBs) are short (∼ms) and luminous (∼10 42 erg s −1) radio pulses detected at extragalactic distances. However, it is possible that FRB counterparts are lurking among catalogs of unclassified transient events. In some scenarios for the FRB engine and emission mechanism, we find that FRB counterparts should have already been detected, thus demonstrating that our technique can successfully test predictions for η. We present constraints on η that improve upon previous observations even in the case where all unclassified transient events in existing surveys are FRB counterparts. Our technique combines the fluence distribution of the FRB population with results from several wide-field blind surveys for fast transients from the optical to the TeV bands. In this work, we demonstrate a technique to estimate the ratio, η, between the energy outputs of FRB counterparts at various wavelengths and the radio-wavelength emission. However, several previous targeted searches for prompt FRB counterparts have yielded no detections and have additionally not reached sufficient sensitivity with respect to the predictions. Many FRB models predict prompt multiwavelength counterparts, which can be used to refine our knowledge of these fundamentals of the FRB phenomenon. The engines that produce extragalactic fast radio bursts (FRBs), and the mechanism by which the emission is generated, remain unknown.
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