The pre-shock gas of SN1006 from HST/ACS observations

TL;DR

This study uses high-resolution HST/ACS images to determine the pre-shock density and structure of SN1006's shock front, providing insights into shock dynamics and interstellar turbulence effects.

Contribution

It offers new measurements of pre-shock density and filament scale length in SN1006 using deep imaging and updated models, testing X-ray emission models and turbulence predictions.

Findings

Pre-shock density estimated between 0.25 and 0.4 cm^{-3}.

Filament ripples consistent with interstellar turbulence with ~20% density fluctuations.

Interaction with interstellar cloud causes blast wave deceleration.

Abstract

We derive the pre-shock density and scale length along the line of sight for the collisionless shock from a deep HST image that resolves the H alpha filament in SN1006 and updated model calculations. The very deep ACS high-resolution image of the Balmer line filament in the northwest (NW) quadrant shows that 0.25 < n_0 < le$ 0.4 cm-3 and that the scale along the line of sight is about 2 x 10^{18} cm, while bright features within the filament correspond to ripples with radii of curvature less than 1/10 that size. The derived densities are within the broad range of earlier density estimates, and they agree well with the ionization time scale derived from the Chandra X-ray spectrum of a region just behind the optical filament. This provides a test for widely used models of the X-ray emission from SNR shocks. The scale and amplitude of the ripples are consistent with expectations for a shock propagating though interstellar gas with ~ 20% density fluctuations on parsec scales as expected from studies of interstellar turbulence. One bulge in the filament corresponds to a knot of ejecta overtaking the blast wave, however. The interaction results from the rapid deceleration of the blast wave as it encounters an interstellar cloud.