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

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 $4.5^{\prime }\times 1.4^{\prime }$ ($\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.

12 pages, 4 figures, 1 table, accepted for publication in The Astrophysical Journal (ApJ)