A bright, high rotation-measure FRB that skewers the M33 halo

We report the detection of a bright fast radio burst, FRB\,191108, with Apertif on the Westerbork Synthesis Radio Telescope (WSRT). The interferometer allows us to localise the FRB to a narrow 5\arcsec\times7\arcmin ellipse by employing both multibeam information within the Apertif phased-array feed (PAF) beam pattern, and across different tied-array beams. The resulting sight line passes close to Local Group galaxy M33, with an impact parameter of only 18\,kpc with respect to the core. It also traverses the much larger circumgalactic medium of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute $\sim$10\% of its dispersion measure of 588\,pc\,cm$^{-3}$. FRB\,191108 has a Faraday rotation measure of +474\,$\pm\,3$\,rad\,m$^{-2}$, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetised plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with $\Delta\nu\approx40$\,MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data

Studying fast radio bursts through population synthesis

Fast Radio Bursts (FRBs) are cosmological transients of unknown origin. While first discovered just over 10 years ago, the enigmatic nature of FRBs is yet to be understood. As exceedingly bright radio emitters, FRBs are visible over immense, cosmological distances. Many are over a billion light years from Earth. If we knew more about FRBs, we could use such bursts to study the evolution of the universe and the extremes of space. This thesis focuses on determining properties of FRBs. Rather than investigating the properties of specific FRBs, we chose to determine properties of the full FRB population. To do so, we use a computational and statistical method called population synthesis. This method involves modelling an intrinsic population, applying selection effects, and then trying to match simulated results to real detections. By taking all of the factors behind a single FRB detection into account, this type of simulation can help to uncover the true nature of FRBs. Recent research suggests FRBs could be powered by neutron stars with strong magnetic fields. We also study the behaviour of neutron stars in other systems, called Low Mass X-ray Binaries (LMXBs). Such systems feature a neutron star accreting mass from a companion star via a so-called accretion disk

Inclination dependence of QPO phase lags in black hole X-ray binaries

Quasi-periodic oscillations (QPOs) with frequencies from $\sim0.05$-$30$ Hz are a common feature in the X-ray emission of accreting black hole binaries. As the QPOs originate from the innermost accretion flow, they provide the opportunity to probe the behaviour of matter in extreme gravity. In this paper, we present a systematic analysis of the inclination dependence of phase lags associated with both Type-B and Type-C QPOs in a sample of 15 Galactic black hole binaries. We find that the phase lag at the Type-C QPO frequency strongly depends on inclination, both in evolution with QPO frequency and sign. Although we find that the Type-B QPO soft lags are associated with high inclination sources, the source sample is too small to confirm this as a significant inclination dependence. These results are consistent with a geometrical origin of Type-C QPOs and a different origin for Type-B and Type-C QPOs. We discuss the possibility that the phase lags originate from a pivoting spectral power law during each QPO cycle, while the inclination dependence arises from differences in dominant relativistic effects. We also search for energy dependences in the Type-C QPO frequency. We confirm this effect in the three known sources (GRS 1915+105, H1743-322 and XTE J1550-564) and newly detect it in XTE J1859+226. Lastly, our results indicate that the unknown inclination sources XTE J1859+226 and MAXI J1543-564 are most consistent with a high inclination.Comment: 16 pages, 10 figures; accepted for publication in MNRA