A detailed study of the interstellar protons toward the TeV $\gamma$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.); a third case of the $\gamma$-rays and ISM spatial correspondence

Abstract

We present a new analysis of the interstellar protons toward the TeV $\gamma$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.). We used the NANTEN2 ${}^{12}$CO($J$ = 1-0) and ATCA & Parkes HI datasets in order to derive the molecular and atomic gas associated with the TeV $\gamma$-ray shell of the SNR. We find that atomic gas over a velocity range from $V_{\mathrm{LSR}}$ = $-4$ km s${}^{-1}$ to 50 km s${}^{-1}$ or 60 km s${}^{-1}$ is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the HI is ascribed to the expanding motion of a few HI shells overlapping toward the SNR but is not due to the Galactic rotation. The total masses of the associated HI and molecular gases are estimated to be $\sim 2.5\times 10^4$ $M_{\odot }$ and $\sim 10^3$ $M_{\odot }$, respectively. A comparison with the H.E.S.S. TeV $\gamma$-rays indicates that the interstellar protons have an average density around 100 cm${}^{-3}$ and shows a good spatial correspondence with the TeV $\gamma$-rays. The total cosmic ray proton energy is estimated to be $\sim 10^{48}$ erg for the hadronic $\gamma$-ray production, which may still be an underestimate by a factor of a few due to a small filling factor of the SNR volume by the interstellar protons. This result presents a third case, after RX J1713.7$-$3946 and HESS J1731$-$347, of the good spatial correspondence between the TeV $\gamma$-rays and the interstellar protons, lending further support for a hadronic component in the $\gamma$-rays from young TeV $\gamma$-ray SNRs.

22 pages, 2 tables, 14 figures, accepted for publication in The Astrophysical Journal (ApJ)

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• The "Carina Flare" Supershell: Probing the Atomic and Molecular ISM in a Galactic Chimney
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• ALMA CO Observations of the Gamma-Ray Supernova Remnant RX J1713.7-3946: Discovery of Shocked Molecular Cloudlets and Filaments at 0.01 pc scales
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• SRG/eROSITA and XMM-Newton observations of Vela Jr
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• Absorption Line Observations of H${}_3^{+}$ and CO in Sight Lines Toward the Vela and W28 Supernova Remnants
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