arXiv subjects

Bojan Arbutina

Publications and source records attributed to Bojan Arbutina.

28 records · Page 2Linked to original sources

arXiv2018

On the foundation of equipartition in supernova remnants

A widely accepted paradigm is that equipartition (eqp) between the energy density of cosmic rays (CRs) and the energy density of the magnetic field cannot be sustained in supernova remnants (SNRs). However, our 3D hydrodynamic supercomputer simulations, coupled with a non-linear diffusive shock acceleration model (NLDSA), provide evidence that eqp may be established at the end of the Sedov phase of evolution in which most SNRs spend the longest portions of their lives. We introduce term "constant partition" for any constant ratio between the CR energy density and the energy density of magnetic field in an SNR, while term "equipartition" should be reserved for the case of approximately the same values of the energy density (also, it is {constant partition} in the order of magnitude) of ultrarelativistic electrons only (or CRs in total) and the energy density of magnetic field. Our simulations suggest that this approximate constant partition does exist in all but the youngest SNRs. We speculate that since evolved SNRs at the end of the Sedov phase of evolution can reach eqp between CRs and magnetic fields, they may be responsible for initializing this type of eqp in the interstellar medium. Additionally, we show that eqp between the electron component of CRs and magnetic field may be used for calculating the magnetic field strength directly from observations of synchrotron emission from SNRs. The values of magnetic field strengths in SNRs given here are approximately 2.5 times lower than values calculated by Arbutina et al. (2012, 2013).

astro-ph.HE↗

arXiv2017

Radio Evolution of Supernova Remnants Including Non-linear Particle Acceleration: Insights from Hydrodynamic Simulations

We present a model for the radio evolution of supernova remnants (SNRs) obtained by using three-dimensional (3D) hydrodynamic simulations, coupled with nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. We model the radio evolution of SNRs on a global level, by performing simulations for wide range of the relevant physical parameters, such as the ambient density, the supernova (SN) explosion energy, the acceleration efficiency and the magnetic field amplification (MFA) efficiency. We attribute the observed spread of radio surface brightnesses for corresponding SNR diameters to the spread of these parameters. In addition to our simulations of type Ia SNRs, we also considered SNR radio evolution in denser, nonuniform circumstellar environment, modified by the progenitor star wind. These simulations start with the mass of the ejecta substantially higher than in the case of a type Ia SN and presumably lower shock speed. The magnetic field is understandably seen as very important for the radio evolution of SNRs. In terms of MFA, we include both resonant and non-resonant modes in our large scale simulations, by implementing models obtained from first-principles, particle-in-cell (PIC) simulations and non-linear magnetohydrodynamical (MHD) simulations. We test the quality and reliability of our models on a sample consisting of Galactic and extragalactic SNRs. Our simulations give $Σ-D$ slopes between -4 and -6 for the full Sedov regime. Recent empirical slopes obtained for the Galactic samples are around -5, while for the extragalactic samples are around -4.

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arXiv2017

Statistical Analysis of Supernova Remnants in the Large Magellanic Cloud

We construct the most complete sample of supernova remnants (SNRs) in any galaxy - the Large Magellanic Cloud (LMC) SNR sample. We study their various properties such as spectral index ($α$), size and surface-brightness. We suggest an association between the spatial distribution, environment density of LMC SNRs and their tendency to be located around supergiant shells. We find evidence that the 16 known type Ia LMC SNRs are expanding in a lower density environment compared to the Core-Collapse (CC) type. The mean diameter of our entire population (74) is 41 pc, which is comparable to nearby galaxies. We didn't find any correlation between the type of SN explosion, ovality or age. The $N(<D)$ relationship of $a={0.96}$ implies that the randomised diameters are readily mimicking such an exponent. The rate of SNe occurring in the LMC is estimated to be $\sim$1 per 200 yr. The mean $α$ of the entire LMC SNR population is $α=-0.52$, which is typical of most SNRs. However, our estimates show a clear flattening of the synchrotron $α$ as the remnants age. As predicted, our CC SNRs sample are significantly brighter radio emitters than the type Ia remnants. We also estimate the $Σ- D$ relation for the LMC to have a slope $\sim3.8$ which is comparable with other nearby galaxies. We also find the residency time of electrons in the galaxy ($4.0-14.3$ Myr), implying that SNRs should be the dominant mechanism for the production and acceleration of CRs.

astro-ph.HE↗

arXiv2016

Interstellar medium structure and the slope of the radio $Σ-D$ relation of supernova remnants

We analyze the influence of fractal structure of the interstellar matter (ISM) density on the parameter values for the radio surface brightness to diameter ($Σ-D$) relation for supernovae remnants (SNRs). We model a dense ISM as a molecular cloud with fractal density structure. SNRs are modelled as spheres of different radius scattered in the modelled ISM. The surface brightness of the SNRs is calculated from the simple relation $Σ\propto ρ^{0.5}D^{-3.5}$ and also from the parametrized more general form $Σ\propto ρ^ηD^{-β_0}$. Our results demonstrate that empirical $Σ-D$ slopes that are steeper than the ones derived from theory, might be partly explained with the fractal structure of the ambient medium into which SNRs expand. The slope of the $Σ-D$ relation steepens if the density of the regions where SNRs are formed is higher. The simple geometrical effects combined with the fractal structure of the ISM can contribute to a steeper empirical $Σ-D$ slopes, especially for older remnants, and this is more pronounced if $Σ$ has a stronger dependence on ambient density.

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arXiv2013

Relativistic Non-Thermal Bremsstrahlung Radiation

By applying a method of virtual quanta we derive formulae for relativistic non-thermal bremsstrahlung radiation from relativistic electrons as well as from protons and heavier particles with power-law momentum distribution $N(p)dp = k p^{-q} dp.$ We show that emission which originates from an electron scattering on an ion, represents the most significant component of relativistic non-thermal bremsstrahlung. Radiation from an ion scattering on electron, known as inverse bremsstrahlung, is shown to be negligible in overall non-thermal bremsstrahlung emission. These results arise from theory refinement, where we introduce the dependence of relativistic kinetic energy of an incident particle, upon the energy of scattered photon. In part, it is also a consequence of a different mass of particles and relativistic effects.

astro-ph.HE↗

arXiv2012

Numerical Code for Fitting Radial Emission Profile of a Shell Supernova Remnant

Expressions for surface brightness distribution and for flux density have been theoretically derived in the case of two simple models of a shell supernova remnant. The models are: a homogenous optically thin emitting shell with constant emissivity and a synchrotron shell source with radial magnetic field. Interactive Data Language (IDL) codes for fitting theoretically derived emission profiles assuming these two models to mean profiles of shell supernova remnants obtained from radio observations have been written.

astro-ph.HE↗

arXiv2007

Radial Dependence of Extinction in Parent Galaxies of Supernovae

The problem of extinction is the most important issue to be dealt with in the process of obtaining true absolute magnitudes of core-collapse (including stripped-envelope) supernovae (SNe). The plane-parallel model, widely used in the past, was shown not to describe extinction adequately. We try to apply an alternative model which introduces radial dependance of extinction in parent galaxies of supernovae. For calculating extinction in our Galaxy we use two different methods and compare the results obtained. Our analysis is primarily focused on a chosen sample of stripped-envelope SNe (Ib/c) for which we find intrinsic peak absolute magnitude $\mathrm{M}_{\mathrm{B}}^{0}=-17.80\pm 0.43$.

astro-ph↗

arXiv2007

Radial Dependence of Extinction in Parent Galaxies of Supernovae

The problem of extinction is the most important issue to be dealt with in the process of obtaining true absolute magnitudes of core-collapse supernovae (SNe). The plane-parallel model which gives absorption dependent on galaxy inclination, widely used in the past, was shown not to describe extinction adequately. We try to apply an alternative model which introduces radial ependence of extinction. A certain trend of dimmer SNe with decreasing radius from the center of a galaxy was found, for a chosen sample of stripped-envelope SNe.

astro-ph↗

arXiv2007

Constraints on the Massive Supernova Progenitors

Generally accepted scheme distinguishes two main classes of supernovae (SNe): Ia resulting from the old stellar population (deflagration of a white dwarf in close binary systems), and SNe of type II and Ib/c whose ancestors are young massive stars (died in a core-collapse explosion). Concerning the latter, there are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to further separate SNe Ib from Ic. We have used assumed SN rates for different SN types in spiral galaxies in an attempt to perform this task. If isolated progenitor hypothesis is correct, our analysis indicates that SNe Ib result from stars of main-sequence mass $23 \mathcal{M}_{\odot} \lesssim \mathcal{M} \lesssim 30 \mathcal{M}_{\odot}$, while the progenitors of SNe Ic are more massive stars with $\mathcal{M} \gtrsim 30 \mathcal{M}_{\odot}$. Alternatively, if the majority of SNe Ib/c appear in close binary systems (CBs) then they would result from the same progenitor population as most of the SNe II, i.e. early B stars with initial masses of order $\mathcal{M} \sim 10 \mathcal{M}_{\odot}$. Future observations of SNe at high-redshift ($z$) and their rate will provide us with unique information on SN progenitors and star-formation history of galaxies. At higher-$z$ (deeper in the cosmic past) we expect to see the lack of type Ia events, i.e. the dominance of core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c), and their potential use as distance indicators at high-$z$, would therefore be of great practical importance.

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arXiv2006

On the magnetic field evolution in shell-like supernova remnants

In this paper we apply and discuss a method for the determination of the magnetic field ($H$) evolution in supernova remnants (SNRs) from radio luminosity at given frequency $ν$ to diameter ($L_\mathrmν-D$) correlation. We assumed that $H$ evolves as $H\propto D^{-δ}$, where $D$ is the diameter of the remnant. Value $δ\approx1.2$ is obtained under the equipartition assumption from the equations for revised equipartition calculation (REC) and by using the data sample from the nearby starburst galaxy M82. We try to investigate whether or not SNRs in M82 are in the equipartition state. This is done by comparison of our empirically obtained $δ$ with the theoretical value expected for the equipartition conditions. Inconsistence between the value obtained for equipartition conditions and adiabatic expansion $(δ=1.5)$ and the value empirically obtained herein, can be explained mainly by the influence of sensitivity selection effects which tend to flatten the slope of the $L_ν-D$ relations for extragalactic samples.

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