Could the interaction of jet and SN ejecta be the cause of X-ray knots observed in a radio galaxy?

TL;DR

This study models jet and supernova ejecta interactions in radio galaxies, finding jet shocks can produce observed X-ray knots and potentially accelerate particles to ultra-high energies, unlike ejecta shocks.

Contribution

It provides a detailed dynamical and spectral modeling of jet-ejecta interactions, demonstrating jet shocks as a plausible origin of X-ray knots and UHECR acceleration in radio galaxies.

Findings

Jet shocks can reproduce the observed size of X-ray knots in M87.

Ejecta shocks are too small to match observed knot scales.

Jets can accelerate protons up to EeV energies, supporting UHECR origin hypotheses.

Abstract

We investigate the interaction between relativistic jets and supernova (SN) ejecta as a potential origin of X-ray knots in radio galaxies, employing knot A in M 87 as a test case. By modeling the dynamical evolution of the interaction, we evaluate this scenario based on particle acceleration efficiency and spatial morphology. Our modeling indicates that the ejecta shock expands to only ~ 30 pc, which is inconsistent with the observed spatial scale of knot A (~ 60 pc). In contrast, the jet shock can successfully reproduce the observed scale after approximately 3000 yr, with the ejecta being accelerated to a bulk velocity of \beta~ 0.43. We fit the multi-wavelength spectral energy distribution (SED) using a one-zone leptonic framework, attributing the X-rays to synchrotron radiation from electrons accelerated up to~1 PeV at the jet shock. The derived magnetic field is approximately 70 uG in the SN ejecta rest frame, which is significantly below the equipartition value. Protons may be accelerated up to ~ EeV, supporting the hypothesis that the jets of radio galaxies (RGs) may be the potential site for ultra-high-energy cosmic-ray (UHECR) acceleration within the framework of the jet-ejecta interaction.