Interstellar protons in the TeV gamma-ray SNR HESS J1731-347:Possible evidence for the coexistence of hadronic and leptonic gamma-rays

Abstract

HESS J1731-347 (G353.6-0.7) is one of the TeV gamma-ray SNRs which shows the shell-like morphology. We have made a new analysis of the interstellar protons toward the SNR by using both the 12CO(J=1-0) and HI datasets. The results indicate that the TeV gamma-ray shell shows significant spatial correlation with the interstellar protons at a velocity range from -90 km/s to -75 km/s, and the distance corresponding to the velocity range is ~5.2 kpc, a factor of 2 larger than the previous figure 3 kpc. The total mass of the interstellar protons is estimated to be 6.4x10^4 M_sun, 25 % of which is atomic gas. We have identified the cold HI gas observed as self-absorption which shows significant correspondence with the northeastern gamma-ray peak. While the good correspondence between the interstellar protons and TeV gamma-rays in the north of the SNR lends support to the hadronic scenario for the TeV gamma-rays, the southern part of the shell shows a break in the correspondence; in particular, the southwestern rim of the SNR shell shows a significant decrease of the interstellar protons by a factor of 2. We argue that this discrepancy can be explained as due to leptonic gamma-rays, because this region well coincides with the bright shell which emit non-thermal radio continuum emission and non-thermal X-rays, suggesting that the gamma-rays of HESS J1713-347 consist of both the hadronic and leptonic components. The leptonic contribution then corresponds to ~20 % of the total gamma-rays. The total energy of cosmic-ray protons is estimated to be 10^49 erg for the gamma-ray energy range of 1 GeV - 100 TeV by assuming that 80 % of the total gamma-ray is of the hadronic origin.

35 pages, 9 figures, 1 table, accepted for publication in The Astrophysical Journal

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• The Mopra Southern Galactic Plane CO Survey - Data Release 3
• 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
• Probing The Local Environment of the Supernova Remnant HESS J1731-347 with CO and CS Observations
• Where are Milky Way's Hadronic PeVatrons?
• ALMA CO Observations of the Mixed-Morphology Supernova Remnant W49B: Efficient Production of Recombining Plasma and Hadronic Gamma-rays via Shock-Cloud Interactions
• Pursuing the origin of the gamma rays in RX J1713.7$-$3946 quantifying the hadronic and leptonic components
• TeV cosmic ray nuclei acceleration in shell-type supernova remnants with hard $\gamma$-ray spectra
• Detection of GeV $\gamma$-ray emission in the direction of HESS J1731-347 with Fermi-LAT
• An Expanding Shell of Neutral Hydrogen Associated with SN 1006: Hints for the Single-Degenerate Origin and Faint Hadronic Gamma-Rays
• XMM-Newton observations of the non-thermal supernova remnant HESS J1731-347 (G353.6-0.7)
• Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources
• Recombining Plasma & Gamma-ray Emission in the Mixed-morphology Supernova Remnant 3C 400.2
• Expansion and ongoing cosmic ray acceleration in HESS J1731-347