Strong evidence for hadron acceleration in Tycho’s supernova remnant

By G. Morlino, D. Caprioli. 2011

250 citations recorded by the source corpus.

Context. Very recent gamma-ray observations of G120.1+1.4 (Tycho’s) supernova remnant (SNR) by Fermi-LAT and VERITAS have provided new fundamental pieces of information for understanding particle acceleration and nonthermal emission in SNRs. Aims. We want to outline a coherent description of Tycho’s properties in terms of SNR evolution, shock hydrodynamics, and multiwavelength emission by accounting for particle acceleration at the forward shock via first-order Fermi mechanism. Methods. We adopt here a quick and reliable semi-analytical approach to nonlinear diffusive shock acceleration. It includes magnetic field amplification due to resonant streaming instability and the dynamical backreaction on the shock of both cosmic rays (CRs) and self-generated magnetic turbulence. Results. We find that Tycho’s forward shock accelerates protons up to at least 500 TeV, channelling into CRs about 10% of its kinetic energy. Moreover, the CR-induced streaming instability is consistent with all the observational evidence of very efficient magnetic field amplification (up to ∼300 μG). In such a strong magnetic field, the velocity of the Alfven waves scattering CRs in the upstream is expected to be enhanced and to make accelerated particles feel an effective compression factor lower than 4, in turn leading to an energy spectrum steeper than the standard prediction ∝E −2 .T his effect is crucial for explaining GeV-to-TeV gamma-ray spectrum as the result of neutral pions decay produced in nuclear collisions between accelerated nuclei and the background gas. Conclusions. The self-consistency of such hadronic scenario, along with the inability of the concurrent leptonic mechanism (inverse Compton scattering of relativistic electrons on several photon backgrounds) to reproduce both the shape and the normalization of the detected gamma-ray emission, represents the first clear and direct radiative evidence that hadron acceleration occurs efficiently in young Galactic SNRs.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b47d580e7634912fe3fa9c59b0421a49b29b3af3

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In Astronomy and Astrophysics

1. A. Spitkovsky
2. D. Caprioli
3. L. Sironi
4. J. Arons
5. D. Giannios
6. A. N. Timokhin
7. M. Petropoulou
8. A. Philippov

In Nuclear and High Energy Physics

1. A. Spitkovsky
2. D. Caprioli
3. L. Sironi
4. J. Arons
5. D. Giannios
6. M. Petropoulou
7. Bing Zhang
8. U. Keshet

Citations in the corpus

• Cosmic-ray acceleration in supernova remnants: non-linear theory revised (2012, background): “NR, whose emission is likely due to the decay of neutral pions produced in nuclear collisions between relativistic nuclei (with energies – 1 – as high as ∼500 TeV, at least) and the background plasma [10]. With a terminology that has become rather popular, we refer to these scenarios as leptonic or ”
• SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY (2013, background): “Also, γ-rays from SNRs are often interpreted to be of hadronic origin (see, e.g., Caprioli 2011; Ackermann et al. 2013), suggesting that nuclei acceleration can be efficient at SNR forward shocks (about 10% in Tycho, see Morlino & Caprioli 2012).”
• SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS (2013, unknown): “Second, ζe/ζp ∼ 1 is inconsistent with the observed ratio for Galactic CRs, which has a differential energy ratio of Ke/p ≃ 0.01 at 10 GeV (Schlickeiser 2002) and observations of supernova remnants constrain the ratio ζe/ζp ∼ 0.001 (Edmon et al. 2011; Morlino & Caprioli 2012).”
• SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. II. MAGNETIC FIELD AMPLIFICATION (2014, background): “…the synchrotron emission produced by relativistic electrons suggest that in young SNRs magnetic fields are 50–100 times larger than in the interstellar medium (ISM; see, e.g., Parizot et al. 2006; Uchiyama et al. 2007; Morlino & Caprioli 2012; Reynoso et al. 2013 for diverse observational facts).”
• The origin of galactic cosmic rays (2013, unknown): “2011) in the TeV range can only be compatible with a hadronic origin (Morlino and Caprioli 2012).”