The search for pulsed radio and gamma-ray emission from the cataclysmic variable system AE Aquarii using MeerKAT and Fermi-LAT data
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Date
2021-12
Authors
Madzime, Spencer Tendai
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The nova-like AE Aquarii was extensively studied using 11 years of data and contemporaneous optical data with the aim to establish pulsed gamma-ray emission at the rotational period (33.08 s) of the white dwarf and the first harmonic (16.54 s). In addition the study was also aimed at identifying pulsed radio emissions at or near the fundamental frequency. Therefore the search of pulsed radio and gammaray emission using MeerKAT (radio) data and upgraded Fermi-LAT pass 8 (gammaray) datasets is presented.
The L-band 45 mins observation of AE Aquarii resulted in the first detection of this source by the MeerKAT telescope. Also, the pulsed radio emission search resulted in the first detection of pulsed emission modulated at the white dwarf’s rotational period (33.08 s). Further investigation resulted in no indication of any pulsations at the first harmonic (16.54 s). The pulsed signal’s overall strength is confined to lower L-band frequencies at the onset of the flare event. No pulsations were significant at the peak of the flare-like event. The spectral variation investigations revealed an optically thin spectrum. This optically thin spectrum observed in the MeerKAT data appears to be uncorrelated to the overall radio spectrum up to 1000 GHz. Hence, a correlation between the MeerKAT data and observations at higher frequencies could
be an exciting topic for in-depth follow-up studies. Investigation for gamma-ray emission from AE Aquarii was conducted using an 11-year baseline of the archived upgraded Fermi-LAT pass 8 dataset. The standard binned and unbinned analyses techniques resulted in no detection of any significant gamma-ray excess in the region of AE Aquarii. However, the search for transient burst-like gamma-ray emission through a light curve revealed sections of the data with an excess significance of 2 s. A search for pulsed gamma-ray emission from these sections resulted in substantial evidence of pulsed signal from some of these sections with excess significance. An additional search for pulsed gamma-ray emission using shorter time bins resulted in detecting more significant pulsations at both the fundamental (33.08 s) and the first harmonic (16.54 s) frequencies. The stacked periodogram displayed clear evidence of particle acceleration from two polar zones of the white dwarf in AE Aquarii, which resulted in a double pulse. Periods contemporaneous to observed optical flares displayed weak pulsations in the noise level. After stacking the periodograms, a significance of over 4 s is seen at the fundamental frequency (33.08 s). A further search for evidence of sporadic burst-like gamma-ray emission from AE Aquarii using refined or more selective filtered data resulted in the detection of AE Aquarii with a significance of 14 s from both the binned and unbinned analyses techniques. The gamma-rays detected from a more constrained refined filtered dataset show clear gamma-ray spectral hardening above the galactic gamma-ray emission. These results have significant implications for follow-up studies of AE Aquarii using ground-based Cherenkov telescopes.
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Keywords
MeerKAT, Dissertation (M.Sc. (Physics))--University of the Fee State, 2021, Gamma-ray emission, Fermi-LAT, Pulsed radio emission