We reported the first detections of the repeating fast radio burst source FRB 121102 across 4 -- 8 GHz receiver of the GBT with the Breakthrough Listen digital backend. We found 21 bursts within the first 60 minutes of a total of 6 hr of observations. At the time of these detection, these observations were the highest burst density reported in the literature, with 18 bursts being detected in the first 30 minutes. A few bursts clearly show temporal sub-structure with distinct spectral properties. These sub-structures superimpose to provide an enhanced peak signal-to-noise ratio at higher trial DM. The most important finding was that the bursts exhibit nearly 100% linear polarization, and a large average rotation measure of around 10^5 rad m^-2 (in the observer’s frame). No circular polarization was found for any burst. These detections were combined with another set of detection made with the Arecibo telescope which was published in Michilli et al. (2018) and created quite a flurry of news.
I have deployed a GPU-accelerated FRB searching pipeline at the GMRT and we have been searching for FRBs from various pulsar surveys. We carried out dedicated DDT observations of
periodic repeating FRB, named FRB 20180916B, which repeats every 16.3 days. We reported the detection of four and seven bursts from observations spanning 3 days using the upgraded GMRT (300-500 MHz) and the GBT (600-1000 MHz), respectively. These detections were the first reported detection of any FRB with the GMRT and first detection of any FRB at the frequency range of 800 MHz to 1 GHz. We identify 30 μs wide structures in one of the bursts at 800 MHz, making it the lowest frequency detection of such structures for this FRB thus far. There is also a clear indication of high activity of the source at a higher frequency during earlier phases of the activity cycle. We identify a gradual decrease in the rotation measure over two years and no significant variations in the dispersion measure.
In Zhang et al. (2018), we reported the detection of 72 new pulses from the repeating fast radio burst FRB 121102 from the GBT using the Breakthrough Listen backend. The new pulses were found with a convolutional neural network in data taken on 2017 August 26, where 21 bursts have been previously detected. Our technique combines neural network detection with dedispersion verification. For the current application, we demonstrate its advantage over a traditional brute-force dedispersion algorithm in terms of higher sensitivity, lower false-positive rates, and faster computational speed. Together with the 21 previously reported pulses, this observation marks the highest number of FRB 121102 pulses from a single observation, totaling 93 pulses in five hours, including 45 pulses within the first 30 minutes. The number of data points reveals trends in pulse fluence, pulse detection rate, and pulse frequency structure. We introduce a new periodicity search technique, based on the Rayleigh test, to analyze the time of arrivals (TOAs), with which we exclude with 99% confidence periodicity in TOAs with periods larger than 5.1 times the model-dependent timestamp uncertainty. In particular, we rule out constant periods ≳10 ms in the barycentric arrival times, though intrinsic periodicity in the time of emission remains plausible.
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