Molecular and atomic gas toward HESS J1745-303 in the Galactic center: Further support for the hadronic scenario

Abstract

We compared TeV γ-rays with new 12CO J = 2-1 data toward HESS J1745-303 in the Galactic center, and confirmed that the molecular cloud MG358.9-0.5 toward (l, b) = (358.°9, - 0.°5) at VLSR = - 100-0 km s-1 shows a reasonable positional agreement with the primary peak (northern part) of the y-ray source. For the southern part of HESS J1745-303, we have seen no CO counterpart, whereas HI gas in the SGPS HI dataset shows a possible counterpart to the γ-ray source. This HI gas may be optically thick, as supported by the HI line shape similar to the optically thick 12CO. We estimate the total mass of interstellar protons including both the molecular and atomic gas to be 2 × 106M ⊙ and the cosmic-ray proton energy to be 6 × 10 48erg in the hadronic scenario. We discuss possible origins of the cosmic-ray protons including the nearby SNR G359.1-0.5. The SNR may be able to explain the northern γ-ray source, but the southern source seems to be too far to be energized by the SNR. As an alternative, we argue that the second-order Fermi acceleration in the inter-clump space surrounded by randomly moving highvelocity clumps may offer a possible mechanism to accelerate protons across the entire HESS source. The large turbulent motion with a velocity dispersion of ∼ 15kms-1 has an energy density two orders of magnitude higher than in the solar vicinity, and is viable as the energy source. © 2012. Astronomical Society of Japan.