Modeling Bright Gamma-ray and Radio Emission at Fast Cloud Shocks

Abstract

Recent observations by the Large Area Telescope (LAT) onboard the Fermi satellite have revealed bright gamma-ray emission from middle-aged supernova remnants (SNRs) inside our Galaxy. These remnants, which also possess bright non-thermal radio shells, are often found to be interacting directly with surrounding gas clouds. We explore the non-thermal emission mechanism at these dynamically evolved SNRs by constructing a hydrodynamical model. Two scenarios of particle acceleration, either a re-acceleration of Galactic cosmic rays (CRs) or an efficient nonlinear diffusive shock acceleration (NLDSA) of particles injected from downstream, are considered. Using parameters inferred from observations, our models are contrasted with the observed spectra of SNR W44. For the re-acceleration case, we predict a significant enhancement of radio and GeV emission as the SNR undergoes a transition into the radiative phase. If sufficiently strong magnetic turbulence is present in the molecular cloud, the re-acceleration scenario can explain the observed broadband spectral properties. The NLDSA scenario also succeeds in explaining the $\gamma$-ray spectrum but fails to reproduce the radio spectral index. Efficient NLDSA also results in a significant post-shock non-thermal pressure that limits the compression during cooling and prevents the formation of a prominent dense shell. Some other interesting differences between the two models in hydrodynamical behavior and resulting spectral features are illustrated.

13 pages, 5 figures, accepted for publication at The Astrophysical Journal

References in corpus (15)

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• Constraints on spinning dust towards Galactic targets with the VSA: a tentative detection of excess microwave emission towards 3C396
• An XMM-Newton study of the mixed-morphology supernova remnant W28 (G6.4-0.1)
• 3-D Model of Broadband Emission from Supernova Remnants Undergoing Non-linear Diffusive Shock Acceleration
• Gamma-Ray Emission from Supernova Remnant Interaction with Molecular Clumps
• Reverse and Forward Shock X-ray Emission in an Evolutionary Model of Supernova Remnants undergoing Efficient Diffusive Shock Acceleration

Cited by in corpus (16)

• ASTRI Mini-Array Core Science at the Observatorio del Teide
• Numerical Simulations of Supernova Remnant Evolution in a Cloudy Interstellar Medium
• Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 GHz and 7 GHz
• Radiative Supernova Remnants and Supernova Feedback
• The Impact of Progenitor Mass Loss on the Dynamical and Spectral Evolution of Supernova Remnants
• Shock-Cloud Interaction in the Southwestern Rim of RX J1713.7$-$3946 Evidenced by Chandra X-ray Observations
• Time evolution of broadband non-thermal emission from supernova remnants in different circumstellar environments
• 3D modeling from the onset of the SN to the full-fledged SNR: Role of an initial ejecta anisotropy on matter mixing
• SNR G39.2-0.3, an Hadronic Cosmic Rays Accelerator
• The Important Role of Cosmic-Ray Re-Acceleration
• Long-term evolution of non-thermal emission from Type Ia and core-collapse supernova remnants in a diversified circumstellar medium
• Multiwavelength studies of G298.6$-$0.0: An old GeV supernova remnant interacting with molecular clouds
• High Energy Gamma Rays from Nebulae Associated with Extragalactic Microquasars and Ultra-Luminous X-ray Sources
• On the Origin of the Gamma-Ray Emission toward SNR CTB 37A with $Fermi$-LAT
• Limits on compression of cosmic rays in supernova remnants
• Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk