Blazar Sheath Illumination of the Outer Molecular Torus: A Resolution of the Seed Photon Problem for the far-GeV Blazar flares

Abstract

Recent multi-wavelength work led by the Boston University blazar group (e.g., Marscher et al. 2010) strongly suggests that a fraction of the blazar flares seen by the Fermi Large Area Telescope (LAT) take place a few to several pc away from the central engine. However, at such distances from the central engine, there is no adequate external photon field to provide the seed photons required for producing the observed GeV emission under leptonic inverse Compton (IC) models. A possible solution is a spine-sheath geometry for the emitting region (MacDonald et al. 2015, but see Nalewajko et al. 2014). Here we use the current view of the molecular torus (e.g., Elitzur, 2012; Netzer 2015) in which the torus extends a few pc beyond the dust sublimation radius with dust clouds distributed with a declining density for decreasing polar angle. We show that for a spine-sheath blazar jet embedded in the torus, the wide beaming pattern of the synchrotron radiation of the relatively slow sheath will heat molecular clouds whose subsequent IR radiation will be seen highly boosted in the spine comoving frame, and that under reasonable conditions this photon field can dominate over the sheath photons directly entering the spine. If the sheath is sufficiently luminous it will sublimate the dust, and if the sheath synchrotron radiation extends to optical-UV energies (as may happen during flares), this will illuminate the sublimated dust clouds to produce emission lines that will vary in unison with the optical-UV continuum, as has been very recently reported for blazar CTA 102 (Jorstad et al. 2017).

Accepted for Publishing in the Astrophysical Journal

References in corpus (11)

• Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
• Reverberation Measurements of the Inner Radius of the Dust Torus in 17 Seyfert Galaxies
• High-Velocity Bipolar Molecular Emission from an AGN Torus
• Constraining the Location of Gamma-Ray Flares in Luminous Blazars
• A multi-zone model for simulating the high energy variability of TeV blazars
• Through The Ring Of Fire: $\gamma$-Ray Variability In Blazars By A Moving Plasmoid Passing A Local Source Of Seed Photons
• Multifrequency Studies of the Peculiar Quasar 4C +21.35 During the 2010 Flaring Activity
• A mid-infrared statistical investigation of clumpy torus model predictions
• The dusty tori of nearby QSOs as constrained by high-resolution mid-IR observations
• Investigating the dusty torus of Seyfert galaxies using SOFIA/FORCAST photometry
• On the Structure of the AGN Torus through the Fraction of Optically-Selected Type 1 AGNs

Cited by in corpus (4)

• The ASKAP-EMU Early Science Project: 888 MHz Radio Continuum Survey of the Large Magellanic Cloud
• Broadband variability and correlation study of 3C 279 during flare of 2017-2018
• Investigation of the Gamma-ray Spectrum of CTA 102 During the Exceptional Flaring State in 2016-2017
• Constraining the $\gamma$-ray Emission Region for Fermi-Detected FSRQs by the Seed Photon Approach