Probing magnetohydrodynamic shocks with high-J CO observations: W28F

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 10 4 cm -3, with the magnetic field strength varying between 45 and 100 μG, and a slightly higher shock velocity for the so-called blue-shock (∼25 km s -1) than for the red one (∼20 km s -1). Our models also satisfactorily account for the pure rotational H 2 emission that is observed with Spitzer. © 2012 ESO.