The discovery that at least some Fast Radio Bursts (FRBs) repeat has ruled out cataclysmic events as the progenitors of these particular bursts. FRB 121102 is the most well-studied repeating FRB but despite extensive monitoring of the source, no underlying pattern in the repetition has previously been identified. Here, we present the results from a radio monitoring campaign of FRB 121102 using the 76 m Lovell telescope. Using the pulses detected in the Lovell data along with pulses from the literature, we report a detection of periodic behaviour of the source over the span of 5 yr of data. We predict that the source is currently ‘off’ and that it should turn ‘on’ for the approximate MJD range 59002−59089 (2020 June 2 to 2020 August 28). This result, along with the recent detection of periodicity from another repeating FRB, highlights the need for long-term monitoring of repeating FRBs at a high cadence. Using simulations, we show that one needs at least 100 h of telescope time to follow-up repeating FRBs at a cadence of 0.5–3 d to detect periodicities in the range of 10–150 d. If the period is real, it shows that repeating FRBs can have a large range in their activity periods that might be difficult to reconcile with neutron star precession models.

We report on a search for fast radio bursts (FRBs) with the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointings amounting to a total on-sky time of 61 days were searched to a dispersion measure (DM) of 3000 pc cm −3 , while the rest (23 days; 29% of the total time) were searched to a DM of 500 pc cm −3 . No FRBs were detected in the pointings observed through 2016 May. We estimate a 95% confidence upper limit on the FRB rate of 3.6 10 3FRBs sky −1 day −1 above a peak flux density of 0.63 Jy at 350 MHz for an intrinsic pulse width of 5 ms. We place constraints on the spectral index α by running simulations for different astrophysical scenarios and cumulative flux density distributions. The nondetection with GBNCC is consistent with the 1.4 GHz rate reported for the Parkes surveys for α>+0.35 in the absence of scattering and free-free absorption and α>−0.3 in the presence of scattering, for a Euclidean flux distribution. The constraints imply that FRBs exhibit either a flat spectrum or a spectral turnover at frequencies above 400 MHz. These constraints also allow estimation of the number of bursts that can be detected with current and upcoming surveys. We predict that CHIME may detect anywhere from several to ∼50 FRBs per day (depending on model assumptions), making it well suited for interesting constraints on spectral index, the log N-log S slope, and pulse profile evolution across its bandwidth (400-800 MHz).

We present Monte-Carlo simulations of a cosmological population of repeating fast radio burst (FRB) sources whose comoving density follows the cosmic star formation rate history. We assume a power-law model for the intrinsic energy distribution for each repeating FRB source located at a randomly chosen position in the sky and simulate their dispersion measures (DMs) and propagation effects along the chosen lines-of-sight to various telescopes. In one scenario, an exponential distribution for the intrinsic wait times between pulses is chosen, and in a second scenario we model the observed pulse arrival times to follow a Weibull distribution. For both models we determine whether the FRB source would be deemed a repeater based on the telescope sensitivity and time spent on follow-up observations. We are unable to rule out the existence of a single FRB population based on comparisons of our simulations with the longest FRB follow-up observations performed. We however rule out the possibility of FRBs 171020 and 010724 repeating with the same rate statistics as FRB 121102 and also constrain the slope of a power-law fit to the FRB energy distribution to be −2.0 < γ < −1.0. All-sky simulations of repeating FRB sources imply that the detection of singular events correspond to the bright tail-end of the adopted energy distribution due to the combination of the increase in volume probed with distance, and the position of the burst in the telescope beam.

Discoveries of rotating radio transients and fast radio bursts (FRBs) in pulsar surveys suggest that more of such transient sources await discovery in archival data sets. Here we report on a single-pulse search for dispersed radio bursts over a wide range of Galactic latitudes (|b| < 60• ) in data previously searched for periodic sources by Burgay et al. We re-detected 20 of the 42 pulsars reported by Burgay et al. and one rotating radio transient reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into account this result, and other recent surveys at Parkes, we corrected for detection sensitivities based on the search software used in the analyses and the different backends used in these surveys and find that the all-sky FRB event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be R = 4.43 FRBs day −1 sky −1 , where the uncertainties represent a 99% confidence interval. While this rate is lower than inferred from previous studies, as we demonstrate, this combined event rate is consistent with the results of all systematic FRB searches at Parkes to date and does not require the need to postulate a dearth of FRBs at intermediate latitudes.

We present 11 detections of FRB 121102 in ∼3 h of observations during its ‘active’ period on the 10th of 2019 September. The detections were made using the newly deployed MeerTRAP system and single pulse detection pipeline at the MeerKAT radio telescope in South Africa. Fortuitously, the Nançay radio telescope observations on this day overlapped with the last hour of MeerKAT observations and resulted in four simultaneous detections. The observations with MeerKAT’s wide band receiver, which extends down to relatively low frequencies (900–1670 MHz usable L-band range), have allowed us to get a detailed look at the complex frequency structure, intensity variations, and frequency-dependent sub-pulse drifting. The drift rates we measure for the full-band and sub-banded data are consistent with those published between 600 and 6500 MHz with a slope of −0.147 ± 0.014 ms−1. Two of the detected bursts exhibit fainter ‘precursors’ separated from the brighter main pulse by ∼28 and ∼34 ms. A follow-up multi-telescope campaign on the 6th and 8th of 2019 October to better understand these frequency drifts and structures over a wide and continuous band was undertaken. No detections resulted, indicating that the source was ‘inactive’ over a broad frequency range during this time.

A new 1.4 GHz 19-element, dual-polarization, cryogenic phased array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of FLAG (Focal L-band Array for the GBT) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beamformed system temperature (T sys ) normalized by aperture efficiency (η) of any phased array receiver to date. The measured T sys /η is 25.4 ± 2.5 K near 1350 MHz for the boresight beam, which is comparable to the performance of the current 1.4 GHz cryogenic single feed receiver on the GBT. The degradation in T sys /η at ∼ 4 (required for Nyquist sampling) and ∼ 8 offsets from the boresight is, respectively, ∼ 1% and ∼ 20% of the boresight value. The survey speed of the PAF with seven formed beams is larger by a factor between 2.1 and 7 compared to a single beam system depending on the observing application. The measured performance, both in frequency and offset from boresight, qualitatively agree with predictions from a rigorous electromagnetic model of the PAF. The astronomical utility of the receiver is demonstrated by observations of the pulsar B0329+54 and an extended H ii region, the Rosette Nebula. The enhanced survey speed with the new PAF receiver will enable the GBT to carry out exciting new science, such as more efficient observations of diffuse, extended neutral hydrogen emission from galactic in-flows and searches for Fast Radio Bursts.

Although high-sensitivity surveys have revealed a number of highly dispersed pulsars in the inner Galaxy, none have so far been found in the Galactic centre (GC) region, which we define to be within a projected distance of 1 pc from Sgr A*. This null result is surprising given that several independent lines of evidence predict a sizable population of neutron stars in the region. Here, we present a detailed analysis of both the canonical and millisecond pulsar populations in the GC and consider free-free absorption and multi-path scattering to be the two main sources of flux density mitigation. We demonstrate that the sensitivity limits of previous surveys are not sufficient to detect GC pulsar population, and investigate the optimum observing frequency for future surveys. Depending on the degree of scattering and free-free absorption in the GC, current surveys constrain the size of the potentially observable population (i.e. those beaming towards us) to be up to 52 canonical pulsars and 10000 millisecond pulsars. We find that the optimum frequency for future surveys is in the range of 9-13 GHz. We also predict that future deeper surveys with the Square Kilometer array will probe a significant portion of the existing radio pulsar population in the GC.

Pulsars are known to emit non-thermal radio emission that is generally a powerlaw function of frequency. In some cases, a turnover is seen at frequencies around 100 MHz. Kijak et al. have reported the presence of a new class of "Gigahertz Peaked Spectrum" (GPS) pulsars that show spectral turnovers at frequencies around 1 GHz. We apply a model based on free-free thermal absorption to explain these turnovers in terms of surrounding material such as the dense environments found in H II regions, Pulsar Wind Nebulae (PWNe), or in cold, partially ionized molecular clouds. We show that the turnover frequency depends on the electron temperature of the environment close to the pulsar, as well as the emission measure along the line of sight. We fitted this model to the radio fluxes of known GPS pulsars and show that it can replicate the GHz turnover. From the thermal absorption model, we demonstrate that normal pulsars would exhibit a GPS-like behaviour if they were in a dense environment. We discuss the application of this model in the context of determining the population of neutron stars within the central parsec of the Galaxy. We show that a non-negligible fraction of this population might exhibit high-frequency spectral turnovers, which has implications on the detectability of these sources in the Galactic centre.