An Expanding Shell of Neutral Hydrogen Associated with SN 1006: Hints for the Single-Degenerate Origin and Faint Hadronic Gamma-Rays

TL;DR

This study reveals an expanding neutral hydrogen shell around SN 1006, supporting a single-degenerate supernova origin and indicating faint hadronic gamma-ray emission consistent with cosmic-ray acceleration models.

Contribution

It provides new HI observations of SN 1006, proposes a wind-blown bubble scenario for its explosion environment, and estimates the cosmic-ray proton energy, linking it to supernova remnant evolution.

Findings

Detected an expanding HI shell with ~4 km/s velocity and ~1000 solar masses.

Supported the single-degenerate progenitor model for SN 1006.

Estimated cosmic-ray proton energy to be ~1.2-2.0 x 10^{47} erg.

Abstract

We report new HI observations of the Type Ia supernova remnant SN 1006 using the Australia Telescope Compact Array with an angular resolution of $4.5' \times 1.4'$ ($\sim$2 pc at the assumed SNR distance of 2.2 kpc). We find an expanding gas motion in position-velocity diagrams of HI with an expansion velocity of $\sim$4 km s$^{-1}$ and a mass of $\sim$1000 $M_\odot$. The spatial extent of the expanding shell is roughly the same as that of SN 1006. We here propose a hypothesis that SN 1006 exploded inside the wind-blown bubble formed by accretion winds from the progenitor system consisting of a white dwarf and a companion star, and then the forward shock has already reached the wind wall. This scenario is consistent with the single-degenerate model. We also derived the total energy of cosmic-ray protons $W_\mathrm{p}$ to be only $\sim$1.2-$2.0 \times 10^{47}$ erg by adopting the averaged interstellar proton density of $\sim$25 cm$^{-3}$. The small value is compatible with the relation between the age and $W_\mathrm{p}$ of other gamma-ray supernova remnants with ages below $\sim$6 kyr. The $W_\mathrm{p}$ value in SN 1006 will possibly increase up to several 10$^{49}$ erg in the next $\sim$5 kyr via the cosmic-ray diffusion into the HI wind-shell.