Supernova remnants in the Local Group – I. A model for the radio luminosity function and visibility times of supernova remnants

Abstract

Supernova remnants (SNRs) in Local Group galaxies offer unique insights into the origin of different types of supernovae. In order to take full advantage of these insights, one must understand the intrinsic and environmental diversity of SNRs in the context of their host galaxies. We introduce a semi-analytic model that reproduces the statistical properties of a radio continuum-selected SNR population, taking into account the detection limits of radio surveys, the range of SN kinetic energies, the measured ISM and stellar mass distribution in the host galaxy from multi-wavelength images and the current understanding of electron acceleration and magnetic field amplification in SNR shocks from first-principle kinetic simulations. Applying our model to the SNR population in M33, we reproduce the SNR radio luminosity function with a median SN rate of ∼ 3.1 × 10 −3 per year and an electron acceleration efficiency, e ∼ 4.2 × 10 −3 . We predict that the radio visibility times of ∼ 70% of M33 SNRs will be determined by their Sedov-Taylor lifetimes, and correlated with the measured ISM column density, N H (t vis ∝ N −a H , with a ∼ 0.33) while the remaining will have visibility times determined by the detection limit of the radio survey. These observational constraints on the visibility time of SNRs will allow us to use SNR catalogs as 'SN surveys' to calculate SN rates and delay time distributions in the Local Group.

Observational Constraints on Late-time Radio Rebrightening of GRB/Supernovae

“…For GRB afterglows, it has been shown that e is fairly narrowly distributed around 0.1 (e.g., Beniamini & van der Horst 2017), and e = 0.1 is also commonly used for SNe Ib/c (Chevalier & Fransson 2006). We note that for the slower shocks in "normal" SNRs (with velocities around a few thousand km s −1 ), e and B can be one to two orders of magnitude lower than assumed here (e.g., Sarbadhicary et al 2017). The ejecta of the GRB/SNe have high kinetic energies and should therefore maintain large velocities (around an order of magnitude faster than the velocities seen in typical SNRs), even as they transition to the Sedov-Taylor phase (Kathirgamaraju et al 2016).…”

“…Because of the likeness to typical SN remnants (SNRs), we refer to GRB/SN radio emission on decades-long scales as "SNR emission" throughout the rest of this paper. After peaking at the Sedov-Taylor time, the radio emission will decline throughout the Sedov-Taylor phase, as the SNR blast wave decelerates (Berezhko & Völk 2004;Barniol Duran & Giannios 2015;Kathirgamaraju et al 2016;Sarbadhicary et al 2017).…”

Supernova remnants in M33: X-ray properties as observed by XMM–Newton

“…M33 has perhaps the best-characterized SNR population of any spiral galaxy (Sabbadin 1979;Dodorico et al 1980;Gordon et al 1998;Long et al 2010;Sarbadhicary et al 2017), making it a prime target to extend these previous works characterizing extragalactic SNRs. In particular, M33, a late-type Sc spiral, is well-suited for X-ray studies of SNRs because of its proximity to the Milky Way at 817±58 kpc (Freedman et al 2001), its close to face-on angle of inclination, i = 56 • ±1 • (Zaritsky et al 1989), and its low foreground absorption (N H ≈6×10 20 cm −2 , Stark et al 1992).…”

Spectrum of Electrons Accelerated in Supernova Remnants

“…Electron Spectrum-Once the instantaneous proton spectrum, f p (p), has been calculated, the instantaneous electron spectrum, f e (p) is calculated as in [45] using the analytical approximation provided by [46]: f e (p) = K ep f p (p) 1 + 0.523(p/p e,max ) 9/4 2 e −p 2 /p 2 e,max , (5) where p e,max is the maximum electron momentum determined by equating the acceleration and synchrotron loss timescales. K ep is the normalization of the electron spectrum relative to that of protons; its value ranges between 10 −2 and 10 −4 [16,47,48] but has no bearing on the spectrum slope.…”