Observations of ionized carbon towards the $\gamma$-ray-bright supernova remnant RX J1713.7-3946

Abstract

The origin of Galactic Cosmic Rays (CRs), particularly at sub-GeV energies, remains uncertain due to their difficulty in being traced. One possible tracer of low-energy CRs is ionised carbon ([C II]), which may be enhanced in regions affected by CR-induced ionisation. We present observations of [C II] 158 $\mu$m line emission across the $\gamma$-ray-bright supernova remnant (SNR) RX J1713.7-3946 obtained with SOFIA. These data are compared with molecular and atomic gas from Mopra (${}^{12}$CO), Nanten (${}^{12}$CO) and SGPS (HI), and high-energy emission from TeV $\gamma$-ray H.E.S.S. and X-ray XMM-Newton. We find [C II] emission follows the atomic gas more closely than molecular gas, particularly in regions near the SNR shock front. Ratios of [C II] intensity to gas column density vary across the remnant, with peak values coinciding with regions of enhanced TeV $\gamma$-ray emission. To put the [C II] in a wider context, we examined pointings from the Herschel GOT C+ survey. Our analysis of the GOT C+ data shows no significant difference in the I[C II]/I[${}^{12}$CO] ratio for observations towards star formation regions, HII regions and SNRs. To assess the origin of carbon ionisation, we model [C II] emissivity using the photoionisation code CLOUDY. We find UV photons and CRs can produce comparable levels of [C II] emission, assuming low-energy CRs (< 1 GeV) are accelerated and trapped within the SNR shock. These results highlight the potential of [C II] as a tracer of CR ionisation and the importance of combining multi-wavelength observations to probe CR interactions in SNRs.

arXiv comment22 pages, 29 figures

References in corpus (41)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• A model for atomic and molecular interstellar gas: The Meudon PDR code
• Photodissociation and photoionisation of atoms and molecules of astrophysical interest
• The H.E.S.S. Galactic plane survey
• The WISE Catalog of Galactic HII Regions
• Massive Stars: Their Environment and Formation
• The Southern Galactic Plane Survey: HI Observations and Analysis
• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• A PDR-Code Comparison Study
• A detailed spectral and morphological study of the gamma-ray supernova remnant RX J1713.7-3946 with H.E.S.S
• The First VERITAS Telescope
• The origin of Galactic cosmic rays: challenges to the standard paradigm
• Collisional Excitation of the [CII] Fine Structure Transition in Interstellar Clouds
• A Herschel [C II] Galactic plane survey II: CO-dark H2 in clouds
• XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source
• A Detailed Study of the Molecular and Atomic Gas Toward the γ-ray SNR RX J1713.7-3946: Spatial TeV γ-ray and ISM Gas Correspondence
• Gamma ray emission from SNR RX J1713.7-3946 and the origin of galactic cosmic rays
• H.E.S.S. observations of RX J1713.7-3946 with improved angular and spectral resolution; evidence for gamma-ray emission extending beyond the X-ray emitting shell
• GREAT/SOFIA atmospheric calibration
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• Low velocity shocks: signatures of turbulent dissipation in diffuse irradiated gas
• The Mopra Southern Galactic Plane CO Survey
• Fine-structure in the nonthermal X-ray emission of SNR RX J1713.7-3946 revealed by Chandra
• A Detailed Study of Molecular Clouds toward the TeV Gamma-Ray SNR G347.3-0.5
• Chemistry in Cosmic-Ray Dominated Regions (CRDRs)
• [CII] observations of H${}_2$ molecular layers in transition clouds
• The Mopra Southern Galactic Plane CO Survey - Data Release 3
• [C II] emission from galactic nuclei in the presence of X-rays
• Spectral properties of nonthermal X-ray emission from the shell-type SNR RX J1713.7-3946 as revealed by XMM-Newton
• A Statistical Analysis of Galactic Radio Supernova Remnants
• Ionized carbon as a tracer of the assembly of interstellar clouds
• Cosmic-ray-induced ionization in molecular clouds adjacent to supernova remnants - Tracing the hadronic origin of GeV gamma radiation
• Far UV and Optical Emissions from Three Very Large Supernova Remnants Located at Unusually High Galactic Latitudes
• Pursuing the origin of the gamma rays in RX J1713.7$-$3946 quantifying the hadronic and leptonic components
• Tracers of the ionization fraction in dense and translucent gas: I. Automated exploitation of massive astrochemical model grids
• The impact of cosmic-ray attenuation on the carbon cycle emission in molecular clouds
• The SOFIA Telescope
• 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
• Dense Gas Towards the RXJ1713.7-3946 Supernova Remnant
• Sub-mm/mm studies of the molecular gas in the Galactic disk; the TeV gamma ray SNR RXJ1713.7-3946 and the W28 high mass star forming region
• Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud