Exploring the link between neutron stars and fast radio bursts

Fast Radio Bursts (FRBs) are extremely bright extragalactic radio flashes, and some of the shortest known astrophysical transients. Most FRBs are only seen once (one-offs), while others repeat. Despite the astounding advances over the last five years, the origin of FRBs remains a mystery, and no multi-wavelength counterparts have been observed. Since extraordinary amounts of energy are required to produce FRBs, compact objects such as neutron stars are potential progenitors. In this thesis, I investigated the properties of repeater and one-off FRBs to study their links to neutron stars with extreme magnetic fields, known as magnetars. To this end, I performed multi-frequency observations and searches of both neutron stars and FRBs. First, I observed high-energy neutron stars at low radio-frequencies, to understand how bright radio bursts could be produced (Ch. 2). I further developed an algorithm to detect faint X-ray transients in an attempt to search for high-energy counterparts to FRBs (Ch. 3). Next, I carried out multi-frequency radio observations of an FRB with a periodic activity cycle, and show that our detections strongly favour an ultra-long period magnetar interpretation (Ch. 4). Finally, I present the discoveries from the Apertif FRB survey, where we found 24 new one-off FRBs that allow us to better characterise the properties of the FRB population (Ch. 5,6). The emission and environment around extragalactic magnetars can explain the complex morphology and propagation properties observed in our FRB sample. Therefore, the results of this thesis strengthen the association of both one-off and repeater FRBs to magnetars.