Highest Frequency Detection of FRB 121102 at 4–8 GHz Using the Breakthrough Listen Digital Backend at the Green Bank Telescope

Abstract

We report the first detections of the repeating fast radio burst source FRB 121102 above 5.2 GHz. Observations were performed using the 4−8 GHz receiver of the Robert C. Byrd Green Bank Telescope with the Breakthrough Listen digital backend. We present the spectral, temporal and polarization properties of 21 bursts detected within the first 60 minutes of a total 6-hour observations. These observations comprise the highest burst density yet reported in the literature, with 18 bursts being detected in the first 30 minutes. A few bursts clearly show temporal sub-structures with distinct spectral properties.These sub-structures superimpose to provide enhanced peak signal-to-noise ratio at higher trial dispersion measures. Broad features occur in ∼ 1 GHz wide subbands that typically differ in peak frequency between bursts within the band.Finer-scale structures (∼ 10 − 50 MHz) within these bursts are consistent with that expected from Galactic diffractive interstellar scintillation. The bursts exhibit nearly 100% linear polarization, and a large average rotation measure of 9.359±0.012 × 10 4 rad m −2 (in the observer's frame). No circular polarization was found for any burst. We measure an approximately constant polarization position angle in the 13 brightest bursts. The peak flux densities of the reported bursts have average values (0.2±0.1 Jy), similar to those seen at lower frequencies (< 3 GHz), while the average burst widths (0.64±0.46 ms) are relatively narrower.Subject headings:

A Sample of Low-energy Bursts from FRB 121102

“…In a large sample of FRB 121102 bursts detected within 4 hours, Gajjar et al (2018) and Zhang et al (2018) found bursts to occur at preferred frequencies in their 4 − 8 GHz band. We show that this behaviour is present at 1.4 GHz as well (Figure 3).…”

“…The detection of a large sample of bursts from FRB 121102, at observing frequencies ranging from 1 to 8 GHz (e.g. Spitler et al 2016;Scholz et al 2016;Law et al 2017;Michilli et al 2018a;Gajjar et al 2018;Spitler et al 2018;Zhang et al 2018;Hessels et al 2019), has led to a variety of observed spectra. For instance, they cannot be consistently described by a single spectral index, some bursts exhibit a frequency dependent profile evolution, and burst spectra from Law et al (2017) are typically limited to 500-MHz wide Gaussian envelopes.…”

On the FRB luminosity function – – II. Event rate density

“…We postpone the spectrum modelling to future work, when a wider frequency coverage is available. The flat-spectrum assumption is driven by the repeater FRB 121102, for which an apparently flat spectrum with ∼ 1 GHz bandwidth was observed (Gajjar et al 2018).…”

FRB coherent emission from decay of Alfvén waves

“…It is firmly established that at least a few milli-second duration, very bright, radio signals that have been detected between about 400 MHz and 7 GHz (known as Fast Radio Bursts or FRBs) are coming from a distance of about a Gpc or more, eg. Lorimer et al 2007; Thornton et al 2013;Spitler et al 2014;Petroff et al 2016;Bannister et al 2017;Law et al 2017;Chatterjee et al 2017;Marcote et al 2017;Tendulkar et al 2017;Gajjar et al 2018;Michilli et al 2018;Farah et al 2018;Shannon et al 2018;Oslowski et al 2019;Kocz et al 2019;Bannister et al 2019;CHIME Collaboration 2019a and2019b;Ravi 2019aRavi , 2019bRavi et al 2019. Many mechanisms have been suggested for the generation of high luminosity coherent radio waves from Fast Radio Bursts (FRBs), eg. Katz (2014Katz ( , 2016, Murase et al (2016;, Kumar et al (2017), Metzger et al (2017), Zhang (2017), Beloborodov (2017), Cordes (2017), Ghisellini & Locatelli (2018), Lu & Kumar (2018), Metzger et al (2019), Thompson (2019), Wang & Lai (2019), ; for a recent review see Katz (2018).…”