Persistent X-ray emission from ASASSN-15lh

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The persistent soft X-ray emission from the location of the so-far most luminous supernova (SN), ASASSN-15lh (or SN 2015L), with L ~ 1E42 erg/s, is puzzling. We show that it can be explained by radiation from the SN-shock accelerated electrons inverse-Compton scattering the intense UV photons. The non-detection in radio requires strong free-free absorption in the dense medium.

Huang Y., Li Z., 2018, ApJ, 859, 123
Full Paper: https://arxiv.org/

The persistent soft X-ray emission from the location of the so-far most luminous supernova (SN), ASASSN-15lh (or SN 2015L), with L ~ 1E42 erg/s, is puzzling. We show that it can be explained by radiation from the SN-shock accelerated electrons inverse-Compton scattering the intense UV photons. The non-detection in radio requires strong free-free absorption in the dense medium.

  • In these interpretations, the circumstellar medium is derived to be a wind ($n\propto R^{-2}$) with mass-loss rate of $\dot M \ga 3 \times10^{-3}M_\odot(v_{\rm w}/10^3 \rm km,s^{-1}) yr^{-1}$, and the initial velocity of the bulk SN ejecta is $\la 0.02c$.

  • These constraints imply a massive ejecta mass of $\ga60(E_0/2\times10^{52} \unit{erg}) M_\odot$ in ASASSN-15lh, and a strong wind ejected by the progenitor star within $\sim8 (v_{\rm w}/10^3 \rm km,s^{-1})^{-1}$ yrs before explosion.