Source properties and population distributions of Fast radio bursts




Bhattacharya, Mukul

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Fast radio bursts (FRBs) are bright millisecond duration transients that are primarily detected from high Galactic latitudes with large dispersion measures which indicates their cosmological origin. Although their observed population has grown rapidly over the past few years, the physical nature of these bursts still remains largely unknown due to the sparse arcminute localisations from current radio transient surveys that hinders their host galaxy identification. Characterising underlying distributions will not just help optimize future searches, but also potentially identify observational sub-classes and provide valuable insights regarding their progenitors, source environment and host galaxy properties.

In this thesis, we investigate the physical properties of FRB sources and further study the binary population classes of these events. First, we discuss a general formalism that we have developed in order to estimate the source properties of FRB progenitors directly from the radio observations. We consider dispersion measure contributions from a Milky Way-type spiral host galaxy, temporal broadening models for pulse propagation through turbulent plasma and a relatively flat FRB energy density spectrum. We then present the results from our Monte Carlo population synthesis code that allows us to directly constrain the properties of the FRB source, its host galaxy and scattering in the intervening plasma from the current observations. We show that the repeating FRB 121102 is likely to be representative of the entire FRB population based on its energy distribution function and the published FRB follow-up observations at present.

We further extend our analysis to constrain the spatial density of these energetic bursts from their observed flux density distributions. We show that these events most likely originate from a relatively young stellar population which is consistent with the theoretical predictions of the coherent curvature radiation model. Lastly, we discuss the astrophysical implications of future FRB detections including a unified emission mechanism for both non-repeating and repeating FRB population classes, empirical constraints on the source intrinsic variability timescales from observed light curves and the wide-ranging applications of localised FRB sources as cosmological probes and independent distance measures in the near future.



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