Gamma-ray emission from middle-aged supernova remnants interacting with molecular clouds: the challenge for current models

Abstract

We compare the $\gamma$-ray spectra from 10 middle-aged supernova remnants (SNRs), which are interacting with molecular clouds (MCs), with the model prediction from widely used escaping scenario and direct interaction scenario. It is found that the $\gamma$-ray data is inconsistent with the escaping scenario statistically, as it predicts a diversity of spectral shape which is not observed. The inconsistency suggests that the free escape boundary adopted in the escaping model is not a good approximation, which challenges our understanding of cosmic ray (CR) escaping in SNRs. In addition, we show that ambient CRs is potentially important for the $\gamma$-ray emission of illuminated MCs external to W28 and W44. In direct interaction scenario, the model involving re-acceleration of pre-existing CRs and adiabatic compression is able to explain the emission from most SNRs. The dispersion shown in the TeV data is naturally explained by different acceleration time of CR particles in SNRs. Re-acceleration of pre-existing CRs suggests a transition of seed particles, which is from thermal injected seed particle in young SNRs to ambient CRs in old SNRs. The transition needs to be tested by future multi-wavelength observation. In the end, we propose that radiative SNR without MC interaction is also able to produce a significant amount of $\gamma$-ray emission. A good candidate is S147. With accumulated Fermi data and CTA in future we expect to detect more remnants like S147.

15 pages and 7 figures. Accepted by MNRAS

References in corpus (15)

• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• Parameterization of Gamma, e^+/- and Neutrino Spectra Produced by p-p Interaction in Astronomical Environment
• Search for extended sources in the Galactic Plane using 6 years of Fermi-Large Area Telescope Pass 8 data above 10 GeV
• Mechanism for spectral break in cosmic ray proton spectrum from Supernova remnant W44
• GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the Galaxy
• Supernova Remnants Interacting with Molecular Clouds: X-ray and Gamma-ray Signatures
• Detailed Investigation of the Gamma-Ray Emission in the Vicinity of SNR W28 with FERMI-LAT
• Modeling Bright Gamma-ray and Radio Emission at Fast Cloud Shocks
• Cosmic ray spectrum in the local Galaxy
• Radio spectral properties and the magnetic field of the SNR S147
• H.E.S.S. detection of TeV emission from the interaction region between the supernova remnant G349.7+0.2 and a molecular cloud
• Probing the gamma-ray emission from HESS J1834-087 using H.E.S.S. and Fermi LAT observations
• Gamma-Ray Emission from Supernova Remnant Interaction with Molecular Clumps
• Time-dependent Diffusive Shock Acceleration in Slow Supernova Remnant Shocks

Cited by in corpus (10)

• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Multiple emission components in the Cygnus cocoon detected from Fermi-LAT observations
• SNR G39.2-0.3, an Hadronic Cosmic Rays Accelerator
• Interaction between Molecular Clouds and MeV-TeV Cosmic-ray Protons Escaped from Supernova Remnants
• Interstellar anatomy of the TeV gamma-ray peak in the IC443 supernova remnant
• And then they were two: detection of non-thermal radio emission from the bow shocks of two runaway stars
• The GeV emission in the field of the star-forming region W30 revisited
• Disclosing the catalog pulsars dominating the Galactic positron flux
• Supernova remnant G46.8-0.3, a new case of interaction with molecular material
• Limits on compression of cosmic rays in supernova remnants