# SUBARU HDS Observations of a Balmer-Dominated Shock in Tycho's Supernova Remnant

## TL;DR

This study uses Subaru Telescope HDS observations to analyze a Balmer-dominated shock in Tycho's supernova remnant, revealing a precursor region likely heated by cosmic rays or fast neutrals, with detailed line profile variations.

## Contribution

First spatially resolved spectroscopic evidence of a precursor in Tycho's supernova remnant, supporting cosmic-ray or neutral precursor models.

## Key findings

- Detection of a broadening and shift in the Ha line profile.
- Identification of a spatial gradient in Ha intensity and line width.
- Evidence consistent with a cosmic-ray precursor.

## Abstract

We present an Ha spectral observation of a Balmer-dominated shock on the eastern side of Tycho's supernova remnant using the Subaru Telescope. Utilizing the High Dispersion Spectrograph (HDS), we measure the spatial variation of the line profile between preshock and postshock gas. Our observation clearly shows a broadening and centroid shift of the narrow-component postshock Ha line relative to the Ha emission from the preshock gas. The observation supports the existence of a thin precursor where gas is heated and accelerated ahead of the shock. Furthermore, the spatial profile of the emission ahead of the Balmer filament shows a gradual gradient in the Ha intensity and line width ahead of the shock. We propose that this region (~10^16 cm) is likely to be the spatially resolved precursor. The line width increases from ~30 up to ~45 km/s, and its central velocity shows a redshift of ~5 km/s across the shock front. The characteristics of the precursor are consistent with a cosmic-ray precursor, although the possibility of a fast neutral precursor is not ruled out.