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TIME RESOLVED RADIO POLARIMETRY OF V404 CYGNI'S 2015 OUTBURST

  • Author / Creator
    Hughes, Andrew
  • Relativistic jets are an ubiquitous element of systems with accreting black holes. These jets carry away a large fraction of the accreted energy which later energizes their surrounding media. On the largest scales, the jets from supermassive black holes found in the center of galaxies provide a powerful feedback mechanism that regulates star formation. Black hole X-ray binaries are their small scale analogs, consisting of a stellar mass black hole accreting from a companion star. The underlying physical processes are fairly (length) scale invariant; however, they evolve on a humanly accessible time-scale due to their smaller size. As synchrotron radiation is the predominant emission mechanism the resulting (radio) waves are linearly polarized with respect to the magnetic field orientation and the local absorption conditions. Here I present VLA observations and a polarimetric analysis of the black hole X-ray binary V404 Cygni taken on June 22nd during its 2015 outburst. The multi-frequency data included simultaneous C (4-8 GHz) and K (20-26 GHz) band radio observations across ~4 continuous hours. The radio frequencies probed the conditions in the radio-loud accretion-powered relativistic jets. After a brief introduction of the emission mechanisms and past observations of similar sources, the evolution of the polarization properties and the frequency-dependent delays are discussed. The high time-resolution light curves showed a tri-peaked temporal structure across all of the observing frequencies. Each peak was delayed to later times at lower frequencies and qualitatively followed the predicted behaviour of the van der Laan synchrotron plasmoid model. The delays were directly measured from the cross-correlation function between light curves of differing central frequencies. The polarization images were made with a regular ~14-min window, constituting one of the highest resolution studies of time-resolved radio polarimetry in flaring black hole X-ray binaries. The polarization properties were extracted from each time bin using both the techniques of rotation measure synthesis and a custom Bayesian forward-modelling approach. The source was observed to be weakly polarized with a polarization angle, fractional linear polarization and rotation measure that was variable in time. The variability points to a rapidly evolving emission environment. However, the system exhibited irregularity during the variability that inhibited the attribution of the observed behaviour to simple jet geometries. The analysis of the weakly polarized emission was limited by the capabilities of the VLA. Future multi-frequency observations will be planned to mitigate these limitations. The routines developed for this thesis can be applied to future observations of rapidly evolving polarized sources, both in black hole X-ray binaries and beyond. Further interpretation will require a more detailed theoretical model that combines the effect of optical depth on observed polarization angle with predictions from a precessing compact steady jet and its ballistic ejecta.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-h8ee-hw29
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.