Targeted Fast Radio Burst Searches with the Efflesberg 100-m Radio Telescope

Abstract

Fast radio bursts (FRBs) are bright, energetic, millisecond duration radio bursts of extragalactic origin. The source of FRBs still remains an open problem. Since the discovery of FRBs in 2007, over 100 FRBs have been detected. Most FRBs are single-burst events, while others are observed to be repeating sources. Due to their cosmological origin, FRBs can be used as probes of the intergalactic medium and the medium of their host galaxies. <br /> Roughly ten FRBs have been localised to a host galaxy. Of those, FRB121102 was both the first discovered repeating FRB and the first FRB localised to a host galaxy, and was the primary motivation for the vast majority of the observations performed in this thesis. The FRB121102 bursting source has been proposed to originate from a magnetar within a supernova remnant (SNR), a scenario that can account for repeating bursts, an associated persistent radio source (PRS), and large Faraday rotation measures (RMs). <br /> Large, single-dish telescopes have high sensitivities and small fields of view, making them ideal for targeted and follow-up surveys. This thesis focuses on targeted FRB searches with single-dish telescopes, with the Effelsberg 100-m radio telescope at the forefront. The surveys in this thesis were performed in order to obtain a better understanding of the origin of FRBs, specifically repeating ones, by observing known FRBs and potential hosts of FRB sources, with each scientific chapter being a different approach to that goal. <br /> The commissioning of a phased array feed (PAF) receiver at Effelsberg is presented in Chapter 3. With PAFs, highly customisable beams can be formed on the sky, providing more flexibility than typical multi-beam receivers while also having a larger field of view. PAFs and their use cases are introduced, along with a detailed discussion on the Effelsberg PAF observations at 1.4 GHz. The main observing targets were PRSs associated with galactic disks or star formation regions to search for FRB121102-like bursting sources, and other FRBs such as two of the repeating FRBs, FRB121102 and FRB180814.J0422+73. No bursts were detected, so upper limits (ULs) to the burst rates were calculated based on the observations. The burst rate of RB121102 was also scaled to each PRS. The scaled rates of five of the eleven PRSs were constrained by the UL rates at the 95% confidence level (CL), rejecting the hypothesis of an FRB121102-like source associated with those PRSs. <br /> Chapter 4 presents the observations of ten superluminous supernovae (SLSNe) and long gamma-ray bursts (LGRBs) with Effelsberg using the S45-mm receiver at 5.3-9.3 GHz. SLSNe and LGRBs were targeted due to the similarities between their host galaxies and the host galaxy of FRB121102, and were therefore observed to search for FRB121102-like sources. As no bursts were detected, UL burst rates and scaled FRB121102 rates to each target were calculated. None of the scaled rates were constrained by the ULs at the 95% CL. Furthermore, a PRS concident with the SLSN PTF10hgi was added as a target and observed with the PAF at Effelsberg and the ultra-wideband-low (UWL) receiver at the Parkes 64-m radio telescope in Australia. The FRB121102 rate scaled to PTF10hgi was excluded at the 99% CL. The apparent clustering of bursts from FRB121102 can be explained with a Weibull distribution. For such a distribution, a non-detection probability of 14% and 16% was calculated for the PAF and UWL observations, respectively. <br /> Chapter 5 investigates the temporal RM evolution of FRB121102. Faraday rotation is the rotation of the linearly polarised plane of a signal induced by the line of sight magnetic field. The rate of this rotation across frequency is quantified by the RM. The first RM measurements of FRB121102 was exceptionally high, 1.46 x 10^5 rad/m^2 in the source reference frame, decreasing down to 1.33 x 10^5 rad/m^2 in seven months. In Chapter 5, sixteen additional FRB121102 RM measurements are presented from burst detections with the Arecibo 305-m radio telescope, the Effelsberg 100-m radio telescope, and the Karl G. Jansky Very Large Array, showing a continued decreasing trend in RM over time down to 9.7 x 10^4 rad/m^2 at the most recent epoch of August 2019. Erratic, short-term RM variations of 10^3 rad/m^2 per week were seen from multiple detections within a 30-day window. The complete RM sample of FRB121102, spanning 2.5 years, was compared to theoretical RM evolution models of magnetars within SNRs. The data were inconsistent with model varieties where the remnant magnetar is surrounded by a constant density interstellar medium. However, the data agree with model varieties where the magnetar is surrounded by a magnetar wind nebula. The age of the FRB121102 bursting source was also estimated based on the RM evolution models and was found to be 6-17 years old at the time of the first FRB121102 RM measurement (at the end of 2016). The RM evolution of FRB121102 is also compared to the Galactic center magnetar, PSR J1745-2900, which has shown a similarly drastic decrease in its absolute RM over time.