Hydrodynamical and radio evolution of young supernova remnant G1.9+0.3 based on the model of diffusive shock acceleration

Abstract

The radio evolution of, so far the youngest known, Galactic supernova remnant (SNR) G1.9+0.3 is investigated by using three-dimensional (3D) hydrodynamic modelling and non-linear kinetic theory of cosmic ray (CR) acceleration in SNRs. We include consistent numerical treatment of magnetic field amplification (MFA) due to resonant streaming instability. Under the assumption that SNR G1.9+0.3 is the result of a Type Ia supernova explosion located near the Galactic Centre, using widely accepted values for explosion energy 10 51 erg and ejecta mass 1.4 M ⊙ , the non-thermal continuum radio emission is calculated. The main purpose of this paper is to explain radio flux brightening measured over recent decades and also predict its future temporal evolution. We estimate that the SNR is now ∼ 120 yr old, expanding in an ambient density of 0.02 cm −3 , and explain its steep radio spectral index only by means of efficient non-linear diffusive shock acceleration (NLDSA). We also make comparison between simulations and observations of this young SNR, in order to test the models and assumptions suggested. Our model prediction of a radio flux density increase of ∼ 1.8 per cent yr −1 during the past two decades agrees well with the measured values. We synthesize the synchrotron spectrum from radio to X-ray and it fits well the Very Large Array, Molonglo Observatory Synthesis Telescope, Effelsberg, Chandra and NuSTAR measurements. We also propose a simplified evolutionary model of the SNR in gamma rays and suggest it may be a promising target for gamma-ray observations at TeV energies with the future generation of instruments like Cherenkov Telescope Array. SNR G1.9+0.3 is the only known Galactic SNR with the increasing flux density and we present here the prediction that the flux density will start to decrease approximately 500 yr from now. We conclude that this is a general property of SNRs in free expansion phase.

Radio observations of supernova remnant G1.9+0.3

“…Such a steep spectral index is characteristic of young SNRs (Urošević 2014). The steep spectra of young SNRs can be caused by quasi-perpendicular magnetic field geometry (Bell et al 2011), turbulent magnetic field amplification (Bell et al 2019), Alfvenic drift effect (Jiang et al 2013), and by pure NLDSA effects which efficiently produce strong magnetic field amplification (Pavlović 2017).…”

“…The SNR G1.9+0.3 is believed to be the youngest in the Milky Way (MW) with an age (calculated from its expansion rate) of ∼150 years (Borkowski et al 2017;De Horta et al 2014;Reynolds et al 2009Reynolds et al , 2008Green et al 2008;Carlton et al 2011). Pavlović (2017) estimated the age of G1.9+0.3 as ∼120 years, based on an analysis of the hydrodynamical and radio evolution of this young SNR. Previous studies suggest G1.9+0.3 is a Type Ia SNR (Borkowski et al 2013).…”

“…Murphy et al (2008) found that the flux density of G1.9+0.3 at 843 MHz increased by (1.22± 0.24 0.16 ) per cent per yr over the last two decades. From simulations based on the non-linear diffuse shock acceleration (NLDSA) model, Pavlović (2017) found that the radio flux density should have increased by ∼ 1.8 per cent per yr over the past two decades. Such behaviour would be consistent with a SNR sweeping up the surrounding Interstellar Medium (ISM) increasing number of particles which can be injected into the NLDSA process, gaining ultra-relativistic energies and emitting synchrotron radiation.…”

“…The beginning of Sedov phase will start around 1700 years after the initial SN explosion. Pavlović (2017) emphasised that in this stage of evolution of G1.9+0.3, we are witnessing the fastest increase in radio brightness this SNR will ever produce. Moreover the steep radio continuum spectrum of G1.9+0.3 obtained from various observations can be explained as a result of the efficient NLDSA accompanying with strong magnetic field amplification (Pavlović 2017).…”

Particle acceleration in interstellar shocks

“…modeling the radio synchrotron emission of astrophysical sources such as supernova remnants (e.g. Berezhko & Völk 2004, Pavlović 2017, Pavlović et. al 2018, besides proton spectrum it is also crucial to know electron spectrum.…”