H$\alpha$ Imaging spectroscopy of Balmer-dominated shocks in Tycho's supernova remnant

TL;DR

This study uses high-resolution Fabry-Pérot spectroscopy to analyze the shock front in Tycho's supernova remnant, revealing broadening of the Hα line and evidence for cosmic-ray and broad-neutral precursors, advancing understanding of shock physics.

Contribution

It provides detailed spatially-resolved measurements of Hα line profiles in Tycho's remnant, confirming broadening and identifying precursor mechanisms with Bayesian analysis.

Findings

Confirmed broadening of the narrow Hα line beyond 20 km/s

Detected widespread intermediate-line emission around 150 km/s

Provided evidence for cosmic-ray and broad-neutral precursors

Abstract

We present Fabry-P\'erot interferometric observations of the narrow H$\alpha$ component in the shock front of the historical supernova remnant Tycho (SN 1572). Using GH$\alpha$FaS (Galaxy H$\alpha$ Fabry-P\'erot Spectrometer) on the William Herschel Telescope, we observed a great portion of the shock front in the northeastern (NE) region of the remnant. The angular resolution of $\sim$1$^{\prime\prime}$ and spectral resolving power of R$\sim$21 000 together with the large field-of-view (3.4$^{\prime}$ $\times$ 3.4$^{\prime}$) of the instrument allow us to measure the narrow H$\alpha$-line width in 73 bins across individual parts of the shock simultaneously and thereby study the indicators of several shock precursors in a large variety of shock front conditions. Compared to previous studies, the detailed spatial resolution of the filament also allows us to mitigate possible artificial broadening of the line from unresolved differential motion and projection. Covering one quarter of the remnant's shell, we confirm the broadening of the narrow H$\alpha$ line beyond its intrinsic width of $\sim$20 km/s and report it to extend over most of the filament, not only the previously investigated dense 'knot g'. Similarly, we confirm and find additional strong evidence for wide-spread intermediate-line ($\sim$150 km/s) emission. Our Bayesian analysis approach allows us to quantify the evidence for this intermediate component as well as a possible split in the narrow line. Suprathermal narrow line widths point toward an additional heating mechanism in the form of a cosmic-ray precursor, while the intermediate component, previously only qualitatively reported as a small non-Gaussian contribution to the narrow component, reveals a broad-neutral precursor.