Searches for Radio Pulsars & Fast Transients and Multiwavelength Studies of Single-pulse Emission

Pulsars are excellent tools for studying a wide array of astrophysical phenomena (e.g. gravitational waves, the interstellar medium, general relativity), yet they are still not fully understood. What are their emission processes and how do they change at different energies? How is giant pulse emission different from regular emission? How are different classes of pulsars (RRATs, magnetars, nulling pulsars, etc.) related? Answering these questions will not only help us to understand pulsars in general, but will also help improve techniques for pulsar searches and timing, gravitational wave searches, and single-pulse searches. The work we present here aims to answer these questions through studies of giant pulse emission, the discovery of new pulsars, and single-pulse studies of a large population of pulsars and RRATs.;We took advantage of open telescope time on the 43-m telescope in Green Bank, WV to conduct a long-term study of giant pulses from the Crab pulsar at 1.2 GHz and 330 MHz. Over a timespan of 15 months, we collected a total of 95000 giant pulses which we correlated with both gamma-ray photons from the Fermi satellite and giant pulses collected at 8.9 GHz. Statistics of these pulses show that their amplitudes follow power-law distributions, with indices in the range of 2.1 to 3.1. The correlation with giant pulses at 8.9 GHz showed that the emission processes at 1.2 GHz and 8.9 GHz are related, despite significant profile differences. The correlation with Fermi gamma-ray photons was to test if increased pair production in the magnetosphere was the cause of giant pulses. Our findings suggest that, while it may play a role, increased pair production is not the dominant cause of giant pulses.;As part of a single-pulse study, we reprocessed the archival Parkes Multibeam Pulsar Survey, discovering six previously unknown pulsars. PSR J0922-52 has a period of 9.68 ms and a DM of 122.4 pc cm-3. PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm-3. PSR J1227-6208 has a period of 34.53 ms, a DM of 362.6 pc cm-3, is in a 6.7 day binary orbit. PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm-3. PSR J1725-3853 is an isolated 4.79-ms pulsar with a DM of 158.2 pc cm-3. PSR J1753-2822 has a period of 18.62 ms, a DM of 298.4 pc cm-3, and is in a 9.3 hour binary orbit. These pulsars were likely missed in earlier processing efforts due to the fact that they have both high DMs and short periods, and also the large number of candidates that needed to be looked through. These discoveries suggest that further pulsars are awaiting discovery in the multibeam survey data.;We also searched for single pulses out to a DM of 5000 pc cm-3 with widths of up to two seconds in our reprocessing of the PMPS data. We recorded single pulses from 264 known pulsars and 15 RRATs. We fit amplitude distributions of the pulsars with lognormal distributions and power-law tails, finding that some pulsars show a deviation from a lognormal distribution in the form of an excess of high-energy pulses. Fitting lognormal distributions to the amplitudes of pulses from RRATs showed similar behavior for most RRATs. Here, however, there seem to be two distinct populations of pulses, with the first population being consistent with noise. For pulsars that were detected in a periodicity search, we computed the ratio of their single-pulse S/N to their FFT S/N and looked for correlations between this ratio and physical parameters of the pulsars. We found a few strong correlations, but they all seem to be due to the strongest correlation between the ratio and spin period

A Study of Single Pulses in the Parkes Multibeam Pulsar Survey

We reprocessed the Parkes Multibeam Pulsar Survey, searching for single pulses out to a DM of 5000 pc cm$^{-3}$ with widths of up to one second. We recorded single pulses from 264 known pulsars and 14 Rotating Radio Transients. We produced amplitude distributions for each pulsar which we fit with log-normal distributions, power-law tails, and a power-law function divided by an exponential function, finding that some pulsars show a deviation from a log-normal distribution in the form of an excess of high-energy pulses. We found that a function consisting of a power-law divided by an exponential fit the distributions of most pulsars better than either log-normal or power-law functions. For pulsars that were detected in a periodicity search, we computed the ratio of their single-pulse signal-to-noise ratios to their signal-to-noise ratios from a Fourier transform and looked for correlations between this ratio and physical parameters of the pulsars. The only correlation found is the expected relationship between this ratio and the spin period. Fitting log-normal distributions to the amplitudes of pulses from RRATs showed similar behaviour for most RRATs. Here, however, there seem to be two distinct distributions of pulses, with the lower-energy distribution being consistent with noise. Pulse-energy distributions for two of the RRATS processed were consistent with those found for normal pulsars, suggesting that pulsars and RRATs have a common emission mechanism, but other factors influence the specific emission properties of each source class.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in MNRA

Spectro-temporal analysis of a sample of bursts from FRB 121102

FRB~121102 was the first Fast Radio Burst (FRB) that was shown to repeat. Since its discovery in 2012, more than two hundred bursts have been detected from the source. These bursts exhibit a diverse range of spectral and temporal characteristics and many questions about their origin and form remain unanswered. Here, we present a sample of radio bursts from FRB 121102 detected using the Lovell telescope at Jodrell Bank Observatory. We show four examples of bursts that show peculiar spectro-temporal characteristics and compare them with properties of bursts of FRB~121102 detected at other observatories. We report on a precursor burst that is separated by just 17~ms from the main burst, the shortest reported separation between two individual bursts to date. We also provide access to data for all the detections of FRB~121102 in this campaign.Comment: 3 pages, 1 Figure, to be published in RNAA

Limits on Absorption from a 332-MHz survey for Fast Radio Bursts

Fast Radio Bursts (FRBs) are bright, extragalactic radio pulses whose origins are still unknown. Until recently, most FRBs have been detected at frequencies greater than 1 GHz with a few exceptions at 800 MHz. The recent discoveries of FRBs at 400 MHz from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope has opened up possibilities for new insights about the progenitors while many other low frequency surveys in the past have failed to find any FRBs. Here, we present results from a FRB survey recently conducted at the Jodrell Bank Observatory at 332 MHz with the 76-m Lovell telescope for a total of 58 days. We did not detect any FRBs in the survey and report a 90$\%$ upper limit of 5500 FRBs per day per sky for a Euclidean Universe above a fluence threshold of 46 Jy ms. We discuss the possibility of absorption as the main cause of non-detections in low frequency (< 800 MHz) searches and invoke different absorption models to explain the same. We find that Induced Compton Scattering alone cannot account for absorption of radio emission and that our simulations favour a combination of Induced Compton Scattering and Free-Free Absorption to explain the non-detections. For a free-free absorption scenario, our constraints on the electron density are consistent with those expected in the post-shock region of the ionized ejecta in Super-Luminous SuperNovae (SLSNe).Comment: 12 pages, 9 Figures, 2 Tables, Second revision submitted to MNRA

A Giant Sample of Giant Pulses from the Crab Pulsar

We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses (GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken with the same telescope and backend and analyzed as one data set. We calculated power-law fits to amplitude distributions for main pulse (MP) and interpulse (IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9 GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2 GHz and 39900 GPs from the GBT were recorded during these contemporaneous observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at 8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP GPs were detected within one spin period of high-frequency IP GPs, with a chance probability of 9%. This indicates that the emission processes at high and low radio frequencies are related, despite significant pulse profile shape differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to see if increased pair production in the magnetosphere is the mechanism responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons were used in this correlation analysis. No significant correlations were found between GPs and gamma-ray photons. This indicates that increased pair production in the magnetosphere is likely not the dominant cause of GPs. Possible methods of GP production may be increased coherence of synchrotron emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap

A search for planetary companions around 800 pulsars from the Jodrell Bank pulsar timing programme

We have searched for planetary companions around 800 pulsars monitored at the Jodrell Bank Observatory, with both circular and eccentric orbits of periods between $20$ days and $17$ years and inclination-dependent planetary masses from $10^{-4}$ to $100\,\mathrm{M}_{\oplus}$. Using a Bayesian framework, we simultaneously model pulsar timing parameters and a stationary noise process with a power-law power spectral density. We put limits on the projected masses of any planetary companions, which reach as low as 1/100th of the mass of the Moon ($\sim 10^{-4}\,\mathrm{M}_{\oplus}$). We find that two-thirds of our pulsars are highly unlikely to host any companions above $2-8\,\mathrm{M}_{\oplus}$. Our results imply that fewer than $0.5\%$ of pulsars could host terrestrial planets as large as those known to orbit PSR B1257$+$12 ($\sim4\,\mathrm{M}_{\oplus}$); however, the smaller planet in this system ($\sim0.02\,\mathrm{M}_{\oplus}$) would be undetectable in $95\%$ of our sample, hidden by both instrumental and intrinsic noise processes, although it is not clear if such tiny planets could exist in isolation. We detect significant periodicities in 15 pulsars, however we find that intrinsic quasi-periodic magnetospheric effects can mimic the influence of a planet, and for the majority of these cases we believe this to be the origin of the detected periodicity. Notably, we find that the highly periodic oscillations in PSR B0144$+$59 are correlated with changes in the pulse profile and therefore can be attributed to magnetospheric effects. We believe the most plausible candidate for planetary companions in our sample is PSR J2007$+$3120.Comment: Accepted for publication in MNRA

The slow rise and recovery of the 2019 Crab pulsar glitch

We present updated measurements of the Crab pulsar glitch of 2019 July 23 using a dataset of pulse arrival times spanning $\sim$5 months. On MJD 58687, the pulsar underwent its seventh largest glitch observed to date, characterised by an instantaneous spin-up of $\sim$1 $\mu$Hz. Following the glitch the pulsar's rotation frequency relaxed exponentially towards pre-glitch values over a timescale of approximately one week, resulting in a permanent frequency increment of $\sim$0.5 $\mu$Hz. Due to our semi-continuous monitoring of the Crab pulsar, we were able to partially resolve a fraction of the total spin-up. This delayed spin-up occurred exponentially over a timescale of $\sim$18 hours. This is the sixth Crab pulsar glitch for which part of the initial rise was resolved in time and this phenomenon has not been observed in any other glitching pulsars, offering a unique opportunity to study the microphysical processes governing interactions between the neutron star interior and the crust.Comment: 5 pages, 3 figure