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

We report new H I observations of the Type Ia supernova remnant (SNR) SN 1006 using the Australia Telescope Compact Array with an angular resolution of 4,.5 x 1'.4 (similar to 2 pc at the assumed SNR distance of 2.2 kpc). We find an expanding gas motion in position-velocity diagrams of H I with an expansion velocity of similar to 4 km s(-1) and a mass of similar to 1000 M-circle dot. 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-p to be only similar to 1.2-2.0 x 10(47) erg by adopting the averaged interstellar proton density of similar to 25 cm(-3). The small value is compatible with the relation between the age and W p of other gamma-ray SNRs with ages below similar to 6 kyr. The W-p value in SN 1006 will possibly increase up to several 10(49) erg in the next similar to 5 kyr via the cosmic-ray diffusion into the H I wind shell.