Probing MHD Shocks with high-J CO observations: W28F

TL;DR

This study combines new CO observations with advanced shock models to analyze supernova remnant W28F, revealing that stationary C-type shocks best explain the observed molecular emissions and constraining shock parameters.

Contribution

It introduces a method integrating high-J CO observations with MHD shock and radiative transfer models to characterize shocks in supernova remnants.

Findings

Stationary C-type shock models reproduce CO emission levels.

Best-fit pre-shock density is 10^4 cm^-3 with magnetic fields of 45-100 μG.

Shock velocities are approximately 25 km/s for blue and 20 km/s for red components.

Abstract

Context. Observing supernova remnants (SNRs) and modelling the shocks they are associated with is the best way to quantify the energy SNRs re-distribute back into the Interstellar Medium (ISM). Aims. We present comparisons of shock models with CO observations in the F knot of the W28 supernova remnant. These comparisons constitute a valuable tool to constrain both the shock characteristics and pre-shock conditions. Methods. New CO observations from the shocked regions with the APEX and SOFIA telescopes are presented and combined. The integrated intensities are compared to the outputs of a grid of models, which were combined from an MHD shock code that calculates the dynamical and chemical structure of these regions, and a radiative transfer module based on the 'large velocity gradient' (LVG) approximation. Results. We base our modelling method on the higher J CO transitions, which unambiguously trace the passage of a shock wave. We provide fits for the blue- and red-lobe components of the observed shocks. We find that only stationary, C-type shock models can reproduce the observed levels of CO emission. Our best models are found for a pre-shock density of 104 cm-3, with the magnetic field strength varying between 45 and 100 {\mu}G, and a higher shock velocity for the so-called blue shock (\sim25 km s-1) than for the red one (\sim20 km s-1). Our models also satisfactorily account for the pure rotational H2 emission that is observed with Spitzer.