Aris Karastergiou

Abstract:

We present the data analysis pipeline, commissioning observations, and initial results from the GREENBURST fast radio burst (FRB) detection system on the Robert C. Byrd Green Bank Telescope (GBT) previously described by Surnis et al., which uses the 21-cm receiver observing commensally with other projects. The pipeline makes use of a state-of-the-art deep learning classifier to winnow down the very large number of false-positive single-pulse candidates that mostly result from radio frequency interference. In our observations, totalling 156.5 d so far, we have detected individual pulses from 20 known radio pulsars that provide an excellent verification of the system performance. We also demonstrate, through blind injection analyses, that our pipeline is complete down to a signal-to-noise threshold of 12. Depending on the observing mode, this translates into peak flux sensitivities in the range 0.14–0.89 Jy. Although no FRBs have been detected to date, we have used our results to update the analysis of Lawrence et al. to constrain the FRB all-sky rate to be 1150+200−180 per day above a peak flux density of 1 Jy. We also constrain the source count index α = 0.84 ± 0.06, which indicates that the source count distribution is substantially flatter than expected from a Euclidean distribution of standard candles (where α = 1.5). We discuss this result in the context of the FRB redshift and luminosity distributions. Finally, we make predictions for detection rates with GREENBURST, as well as other ongoing and planned FRB experiments.

Abstract:

Pulsar radio emission and its polarization are observed to evolvewith frequency. This frequency dependence is key to the emission mechanism and the structure of the radio beam.With the new ultra-wideband receiver (UWL) on the Parkes radio telescope we are able, for the first time, to observe how pulsar profiles evolve over a broad continuous bandwidth of 700-4000 MHz.We describe here a technique for processing broad-band polarimetric observations to establish a meaningful alignment and visualize the data across the band.We apply this to observations of PSRs J1056-6258 and J1359-6038, chosen due to previously unresolved questions about the frequency evolution of their emission. Application of our technique reveals that it is possible to align the polarization position angle (PA) across a broad frequency range when constrained to applying only corrections for dispersion and Faraday rotation to do so. However, this does not correspond to aligned intensity profiles for these two sources. We find that it is possible to convert these misalignments into emission height range estimates that are consistent with published and simulated values, suggesting that they can be attributed to relativistic effects in the magnetosphere. We discuss this work in the context of the radio beam structure and prepare the ground for a wider study of pulsar emission using broad-band polarimetric data.

Abstract:

© 2020 The Author(s). We report here on initial results from the Thousand-Pulsar-Array (TPA) programme, part of the Large Survey Project 'MeerTime' on the MeerKAT telescope. The interferometer is used in the tied-array mode in the band from 856 to 1712 MHz, and the wide band coupled with the large collecting area and low receiver temperature make it an excellent telescope for the study of radio pulsars. The TPA is a 5 year project, which aims at to observing (a) more than 1000 pulsars to obtain high-fidelity pulse profiles, (b) some 500 of these pulsars over multiple epochs, and (c) long sequences of single-pulse trains from several hundred pulsars. The scientific outcomes from the programme will include the determination of pulsar geometries, the location of the radio emission within the pulsarmagnetosphere, the connection between the magnetosphere and the crust and core of the star, tighter constraints on the nature of the radio emission itself, as well as interstellar medium studies. First, results presented here include updated dispersion measures, 26 pulsars with Faraday rotation measures derived for the first time, and a description of interesting emission phenomena observed thus far.