Understanding hadronic gamma-ray emission from supernova remnants

Caprioli, Damiano

doi:10.1088/1475-7516/2011/05/026

Cited by 35 publications

(22 citation statements)

References 154 publications

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“…1 in [32]), which is consistent with the γ-ray emission observed from young supernova remnants ( Fig. 3 in [32]). The typical injection 2 Arbutina et al [31] argue that K is smaller if the injection energy is comparable to or larger than the electron's rest mass energy.…”

Section: Basic Assumptionssupporting

confidence: 88%

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Revisiting the Equipartition Assumption in Star-Forming Galaxies

Seta¹,

Beck

2019

Galaxies

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Energy equipartition between cosmic rays and magnetic fields is often assumed to infer magnetic field properties from the synchrotron observations of star-forming galaxies. However, there is no compelling physical reason to expect the same. We aim to explore the validity of the energy equipartition assumption. After describing popular arguments in favour of the assumption, we first discuss observational results that support it at large scales and how certain observations show significant deviations from equipartition at scales smaller than ≈ 1 kpc , probably related to the propagation length of the cosmic rays. Then, we test the energy equipartition assumption using test-particle and magnetohydrodynamic (MHD) simulations. From the results of the simulations, we find that the energy equipartition assumption is not valid at scales smaller than the driving scale of the ISM turbulence (≈ 100 pc in spiral galaxies), which can be regarded as the lower limit for the scale beyond which equipartition is valid. We suggest that one must be aware of the dynamical scales in the system before assuming energy equipartition to extract magnetic field information from synchrotron observations. Finally, we present ideas for future observations and simulations to investigate in more detail under which conditions the equipartition assumption is valid or not.

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Section: Basic Assumptionssupporting

confidence: 88%

“…2 For strong shocks and an adiabatic index of 5/3, the energy spectrum is predicted to have an initial (injection) spectral index of = 2.0 − 2.4 ( Fig. 1 in [32]), which is consistent with the γ-ray emission observed from young supernova remnants ( Fig. 3 in [32]).…”

Section: Basic Assumptionssupporting

confidence: 68%

Revisiting the Equipartition Assumption in Star-Forming Galaxies

Seta¹,

Beck

2019

Galaxies

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“…The photon energy density for the CMB is u CM B = 0.25 eV cm −3 and for the starlight photons can be computed from equation (5) to be u SL (r) = hν 2 0 n SL (ν 0 , r), where ν 0 is taken to be the peak frequency. Finally,n e in equation (8) refers to the average thermal electron density and is taken to bē n e ≈ 0.01 cm −3 [65][66][67][68][69].…”

Section: Solution To the Diffusion Equationmentioning

confidence: 99%

“…with β = 0.49 and r c = 54 [104] and assuming n e,0 ∼ 0.1 cm −3 [68,69]. The neutral pion mass is m π 0 = 135 GeV, ξ gives the pion multiplicity taken to be ξ = 2 for π 0 , and σ pp = 32 mbarn is the proton collision cross-section.…”

Section: B Emissions From Cosmic Rays Of Hadronic Originmentioning

confidence: 99%

Exploring a cosmic-ray origin of the multiwavelength emission in M31

2019

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A recent detection of spatially extended gamma-ray emission in the central region of the Andromeda galaxy (M31) has led to several possible explanations being put forth, including dark matter annihilation and millisecond pulsars. Another possibility is that the emission in M31 can be accounted for with a purely astrophysical cosmic-ray (CR) scenario. This scenario would lead to a rich multi-wavelength emission that can, in turn, be used to test it. Relativistic cosmic-ray electrons (CRe) in magnetic fields produce radio emission through synchrotron radiation, while X-rays and gamma rays are produced through inverse Compton scattering. Additionally, collisions of primary cosmic-ray protons (CRp) in the interstellar medium produce charged and neutral pions that then decay into secondary CRe (detectable through radiative processes) and gamma-rays. Here, we explore the viability of a CR origin for multi-wavelength emission in M31, taking into consideration three scenarios: a CR scenario dominated by primary CRe, one dominated by CRp and the resulting secondary CRe and gamma rays from neutral pion decay, and a final case in which both of these components exist simultaneously. We find that the multi-component model is the most promising, and is able to fit the multi-wavelength spectrum for a variety of astrophysical parameters consistent with previous studies of M31 and of cosmic-ray physics. However, the CR power injection implied by our models exceeds the estimated CR power injection from typical astrophysical cosmic-ray sources such as supernovae.

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“…As η increases, so too does the efficiency of magnetic field amplification and thus the velocity of magnetic perturbations responsible for scattering CRs. Since Alfvén waves generated by CRs tend to travel against the fluid, this increase in magnetic field corresponds to a decrease in the effective compression ratio felt by CRs, resulting in a steepening of their spectrum [see 29,49,50].…”

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confidence: 99%

Spectrum of Electrons Accelerated in Supernova Remnants

Diesing

Caprioli

2019

Phys. Rev. Lett.

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Using a semi-analytic model of non-linear diffusive shock acceleration, we model the total spectrum of cosmic ray (CR) electrons accelerated by supernova remnants (SNRs). Because electrons experience synchrotron losses in the amplified magnetic fields characteristic of SNRs, they exhibit substantially steeper spectra than protons. In particular, we find that the difference between the electron and proton spectral index (power law slope) ranges from 0.1 to 0.4. Our findings must be reckoned with theories of Galactic CR transport, which often assume that electrons and protons are injected with the same slope, and may especially have implications for the observed "positron excess."

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Understanding hadronic gamma-ray emission from supernova remnants

Cited by 35 publications

References 154 publications

Revisiting the Equipartition Assumption in Star-Forming Galaxies

Revisiting the Equipartition Assumption in Star-Forming Galaxies

Exploring a cosmic-ray origin of the multiwavelength emission in M31

Spectrum of Electrons Accelerated in Supernova Remnants

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