Abstract
We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in AGN in a temporary steady state. The new model implementations are used to fit snap-shot spectral energy distributions of a representative set of Fermi-LAT detected blazars from the first LAT AGN catalogue. We find that the leptonic model is capable of producing acceptable fits to the SEDs of almost all blazars with reasonable parameters close to equipartition between the magnetic field and the relativistic electron population. If charge neutrality in leptonic models is provided by cold protons, our fits indicate that the kinetic energy carried by the jet should be dominated by protons. We also find satisfactory representations of the snapshot SEDs of most blazars in our sample with the hadronic model presented here. All of our hadronic model fits require powers in relativistic protons in the range 1047 – 1049 erg/s. As a potential way to distinguish between the leptonic and hadronic high-energy emission models considered here, we suggest diagnostics based on the predicted X-ray and γ -ray polarization, which are drastically different for the two types of models.
Highlights
The spectral energy distributions (SEDs) of blazars are characterized by non-thermal continuum spectra with a broad low-frequency component in the radio – UV or Xray frequency range and a highfrequency component from X-rays to γ-rays
Blazars are sub-divided based on the location of their synchrotron peak: Low-Synchrotron-Peaked (LSP) blazars, consisting of FSRQs and Low-frequency-peaked BL Lac objects (LBLs) have νsy < 1014 Hz; Intermediate-SynchrotronPeaked (ISP) blazars
The radiative output throughout the electromagnetic spectrum is assumed to be dominated by leptons, while any protons that are likely present in the outflow, are not accelerated to sufficiently high energies to contribute significantly to the radiative output
Summary
The spectral energy distributions (SEDs) of blazars are characterized by non-thermal continuum spectra with a broad low-frequency component in the radio – UV or Xray frequency range (generally agreed to be due to synchrotron radiation of relativistic electrons) and a highfrequency component from X-rays to γ-rays. While it is generally accepted that the low-frequency emission component in blazars SEDs is synchrotron emission from relativistic electrons in the jet, the origin of the high-energy emission is still controversial. The high-energy emission is most plausibly explained by Compton scattering of low-energy photons by the same electrons producing the synchrotron emission at lower frequencies [3, 4, 11, 16, 24] In hadronic models, both primary electrons and protons are accelerated to ultrarelativistic energies, with protons exceeding the threshold for pγ photopion production on the soft photon field in the emission region.
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