LEPTONIC AND HADRONIC MODELING OFFERMI-DETECTED BLAZARS

Abstract

We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in active galactic nuclei in a temporary steady state. For the leptonic model, a temporary equilibrium between particle injection/acceleration, radiative cooling, and escape from a spherical emission region is evaluated, and the self-consistent radiative output is calculated. For the hadronic model, a temporary equilibrium between particle injection/acceleration, radiative and adiabatic cooling, and escape is evaluated for both primary electrons and protons. A new, semianalytical method to evaluate the radiative output from cascades initiated by internal γ γ pair production is presented. We use our codes to fit snapshot spectral energy distributions (SEDs) of a representative set of Fermi-LAT-detected blazars. We find that the leptonic model provides acceptable fits to the SEDs of almost all blazars with parameters close to equipartition between the magnetic field and the relativistic electron population. However, the hard γ -ray spectrum of AO 0235+164, in contrast to the very steep IR-optical-UV continuum, poses a severe problem for the leptonic model. If charge neutrality in leptonic models is provided by cold protons, the kinetic energy carried by the jet should be dominated by protons. We find satisfactory representations of the snapshot SEDs of most blazars in our sample with the hadronic model presented here. However, in the case of two quasars the characteristic break at a few GeV energies cannot be well modeled. All of our hadronic model fits require powers in relativistic protons in the range L p ∼ 10 47 -10 49 erg s −1 .

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

“…In summary, we prefer a strongly magnetized emission region, in which fast disturbances can be the driver of the flaring activities. Observations and spectral variability fittings have shown that the typical Lorentz factor of the blazar emission region is within a few tens (e.g., Jorstad et al 2005;Böttcher et al 2013). This is likely to be the upper limit of the shock speed.…”

“…Several papers have demonstrated that the observed polarization signatures may indicate a helical magnetic structure (Lyutikov et al 2005;Pushkarev et al 2005;Zhang et al 2015). The high-energy component, from X-rays to γ-rays, is usually interpreted as originating from inverse Compton scattering by the same nonthermal electrons of soft seed photons (e.g., Marscher & Gear 1985;Dermer et al 1992;Sikora et al 1994), but a hadronic origin cannot be ruled out (e.g., Mannheim & Biermann 1992;Mücke & Protheroe 2001;Böttcher et al 2013). Both spectral components of blazars exhibit fast variability.…”

“…Based on the causality relation, R  δct, where δ is the Doppler factor and t is the observed flaring timescale, the size of the emission region R in the comoving frame of the emission region should generally be within 0.1 pc. Therefore, it is often argued in the blazar spectral variability fittings that the blazar emission region is a small region near the broad line region of the blazar jet (e.g., Tavecchio et al 2010;Böttcher et al 2013;Barnacka et al 2014).…”

MULTIWAVELENGTH STUDY OF QUIESCENT STATES OF Mrk 421 WITH UNPRECEDENTED HARD X-RAY COVERAGE PROVIDED BY NuSTAR IN 2013

“…We can constrain the properties of the jet emission region more precisely by directly modeling the multiwavelength SED data shown in Figure 13 with a standard one-zone SSC model. Specifically, we apply an equilibrium version of the SSC model from Böttcher & Chiang (2002), fully described in Böttcher et al (2013). This model has already been used to represent Mrk 421 in two different states (Acciari et al 2009).…”

Jet Signatures in the Spectra of Accreting Black Holes

“…Here, we limit our analysis to leptonic models in which the electrons are the primary radiators. For a review of the features of both leptonic and hadronic models as applied to blazars, see e.g., Böttcher (2010), Böttcher et al (2013).…”