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Abstract:
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Supernova (SN) explosions disperse the different heavy elements across the Uni
verse. These elements are the building blocks which make up the world around and
inside us. Supernova remnants (SNRs) are extraordinary astronomical objects that
are also of high scientific interest, because they provide insights into aforementioned
supernova explosion mechanisms, and because they are important sources of Galac
tic cosmic rays (CRs). Radio observations are among the oldest means to study these
objects. The radio luminosity and spectra of SNRs, especially young ones, requires
active acceleration of electrons by the SNR shocks. In this doctoral dissertation,
radio evolution of SNRs is investigated by using three-dimensional hydrodynamic
modelling and non-linear diffusive shock acceleration of CRs in SNRs.
Hydrodynamic simulations, developed and adopted in this dissertation, allow us
to explicitly account for the shock modification by CRs. We also include consistent
numerical treatment of magnetic field amplification (MFA) due to CR resonant and
non-resonant streaming instabilities. We modelled the peculiar nature of radio evo
lution of the youngest known Galactic SNR G1.9+0.3 and concluded that increasing
radio emission is a common occurrence among very young SNRs. Our model ena
bled us to make important conclusions about the present and predictions about the
future properties of radio emission from this SNR. We also developed more general
model of the radio evolution of SNRs, by performing simulations for wide range of
the relevant physical parameters, such as the ambient density, the supernova ex
plosion energy, the acceleration efficiency and the MFA efficiency. We confirm the
reliability of our radio evolutionary tracks on a observation sample consisting of
Galactic and extragalactic SNRs.
This dissertation also deals with one of the most important questions surroun
ding our current understanding of the magnetic fields in SNRs. We conclude that
equipartition is a justified assumption especially between the CR electrons and the
magnetic fields in evolved SNRs, in the Sedov-Taylor phase of evolution. Our work
also offers a possible explanation how can equipartition between CRs and magnetic
field in the interstellar medium be achieved.
Type of modeling, presented in this thesis, is expected to be a useful tool for fu
ture observers working on powerful radio telescopes such as ALMA, MWA, ASKAP,
SKA and FAST. Simulations should provide important information about the evolu
tionary stage of the observed SNRs, as well as to characterize the physical conditions
in the shocks where the relativistic particles are accelerated. Simulations could help
us to predict the science output of future large scale surveys, as well as to explain
new, often unexpected results obtained by observations. |