THE HADRONIC MODEL OF ACTIVE GALACTIC NUCLEI A. Mastichiadis University of Athens

TALK OUTLINE High Energy Emission from Active Galactic Nuclei Hadronic Models: key ideas and processes Hadronic models as dynamical systems

GAMMA-RAYS AND AGN Fermi gamma-ray detector 2 nd LAT AGN catalog: 886 sources (2011) 395 BLLac objects 315 FSRQs 156 blazars of unknown type c.f. EGRET catalog: 66 AGN (1995) COS-B catalog: 1 AGN (1983) Fermi

RADIO IMAGES OF GAMMA-RAY AGN

RADIO-LOUD AGN Blazar (ΒL Lac + Quasars) radiogalaxy Gamma-ray emission beamed and associated with jets. Open questions: Emission mechanism (leptonic or hadronic) Jet composition (electron-proton; electron-positron, B) Emission zone – location of energy dissipation

BLAZAR PROPERTIES Compact, flat spectrum radio sources. Superluminal motion  beaming  emission from inside the jet. Broad (radio-γ) non-thermal continuum. Variable at all energies – correlations! Short variability  emission from a localized region (R~c.Δt)

NON-THERMAL EMISSION Broad emission – no thermal signatures  emission from tenuous plasma. Radiation from ultrarelativistic electrons and protons  acceleration of particles to high energies. If high energy particles are electrons 1. synchrotron radiation e + B  e + B + γ 2. inverse Compton scattering e + γ  e + γ (gamma-ray production mechanism) However, gamma-rays can be absorbed from 3. photon-photon absorption γ + γ  e+ + e-

THE LEPTONIC AGN MODEL Log γ Log Ν B-fieldsoft photons inverse comptonsynchrotron Active Region aka The Blob: Relativistic Electrons

INTERACTIONS OF PROTONS WITH PHOTON FIELDS photopair production photomeson production photopair photomeson Loss timescale

THE HADRONIC MODEL: PHYSICAL PROCESSES IN A NUTSHELL Courtesy of R.J. Protheroe leptonic hadronic

THE HADRONIC AGN MODEL Log γ Log Ν synchrotron Active Region aka The Blob: Relativistic Electrons and Protons Proton distribution Gamma-rays from proton induced radiation mechanisms

EMISSION MODELS: A COMPARISON LEPTONIC MODELS Accelerate electrons to high energies. Few and easy to model processes. Few free parameters. Advanced: Time-dependent, self-consistent. Good fits to MW blazar observations. HADRONIC MODELS Accelerate protons to high energies. Many and difficult to model processes. Many free parameters. Nor time dependent, neither self-consistent. Good fits to MW blazar observations. WHY BOTHER?

ORIGIN OF COSMIC RAYS Auger: Positive correlation signal (99% conf.) with AGN catalog: Clustering within ~75 Mpc 2/27 events within ~3 deg from Cen A

HIGH ENERGY NEUTRINO ASTRONOMY Ιf hadronic: AGN sources of UHE neutrinos  ICE CUBE. Other potential sources: GRBs. So far, upper limits only.

AGN: SOURCES OF COSMIC RAYS AND UHE NEUTRINOS?

TIME-DEPENDENT AGN HADRONIC MODEL ASSUMPTIONS Injection of high energy protons – proton energy and luminosity are free parameters. Protons cool by (i) synchrotron (ii) photopair (Bethe-Heitler) (iii) photopion (neutral/charged) Model (ii) from MC results of Protheroe & Johnson (1996) (iii) from SOPHIA code (Muecke et al 2000). Study the simultaneous evolution of protons and secondaries through time-dependent, energy conserving kinetic equations. No external photons / no electron injection (pure hadronic model).  keep free parameters to a minimum (R, B, γ p, L p ) AIMS 1. Study photon spectral formation simultaneously with neutrino and proton spectra (Cosmic Rays at source). 2. Calculate efficiencies (e.g. photon luminosity/proton luminosity) 3. Study expected time signatures (as in leptonic models). NEW

PROTON INJECTION PROTON DISTRIBUTION FUNCTION PROTON LOSSES PROTON ESCAPE ELECTRONS- POSITRONS PHOTONS OBSERVED SPECTRUM Leptonic processes

Protons: injection Electrons: Photons: Neutrinos: Neutrons: Bethe-Heitler proton triplet ssa γγ annihilationphotopion synchrotron pair production

INJECTION OF SECONDARΥ ELECTRONS - RESULTING PHOTON SPECTRA Bethe-Heitler electrons photopion electrons γγ electrons R = 3e16 cm B = 1 G γ p = 2e6 l p = 0.4 electrons photons S. Dimitrakoudis et al., in preparation

PHOTON AND NEUTRINO SPECTRA Power law proton injection injected protons photons neutrinos neutrons Photon spectra --different proton indices p Neutrino spectra --different proton indices p p=1.5 p=2.5 p=1.5 p=2.5 S. Dimitrakoudis et al., in preparation

INCREASING THE PROTON INJECTED ENERGY R = 3e16 cm B = 1 G l p = 0.4 γ p = 3e5γ p = 3e6γ p = 3e7

INCREASING THE PROTON INJECTED LUMINOSITY log lp B=1 G Proton injected luminosity is increased by a factor 3 linear quadratic linear quadratic onset of supercriticality R=3e16 cm highly non-linear

AUTOMATIC PHOTON QUENCHING Stawarz & Kirk 2007 Petropoulou & AM 2011 Injected gamma-ray luminosity Escaping luminosity gamma-rays soft photons Gamma-rays can be self-quenched: Non-linear network of photon-photon annihilation electron synchrotron radiation Operates independently of soft photons Poses a strong limit on the gamma-ray luminosity of a source quenched gamma-rays ‘reprocessed’ gamma-rays l γ,crit

PROTONS  GAMMA-RAYS – escape | | | quenching | | (self-generated) | SOFT PHOTONS |_____________| Soft photons from γ-ray quenching pump proton energy  proton losses  more secondaries  more γ-rays Exponentiation starts when γ-rays enter the quenching regime. PHOTON QUENCHING AND PROTON SUPERCRITICALITY γ-ray quenching regime γ-ray quenching regime Photon spectra for various monoenergetic proton injection energies just before supercriticality

TOWARDS AN ANALYTIC SOLUTION Retain only `key’ processes –Photomeson production –Electron synchrotron radiation –Photon-photon pair production Replace electron synchrotron by the radiated photon spectrum Electrons from photomeson  `hard’ photons Electrons from γγ absorption  `soft’ photons (important only when quenching operates) Rationale: fast electron cooling  Electron equation can be neglected Use simplified expressions (δ-functions) for cross-sections and emissivities Distributions to be determined - Protonsn p - Hard photonsn h - Soft photonsn s assumed to be monoenergetic Parameters of the problem - Proton injection rate Q 0 - Proton escape timescale τ p - Distribution of external photons n ex n ex is needed to start photomeson reactions and it is independent of time Petropoulou & AM 2012

SIMPLIFIED EQUATIONS injection escape photomeson losses on external photons injection due to photomeson on external photons photomeson losses on soft photons injection due to photomeson on soft photons absorption on soft photons (creation of electron- positron pairs) injection (from radiation of electron-positron pairs) quenching absorption on external photons (creation of electron- positron pairs) injection (from radiation of electron-positron pairs)

FIRST STEP Ignore photon-photon absorption of hard photons on external and solve analytically

RESULTS System goes from limit cycle behaviour to damped oscillations to steady state

NEXT STEP Add extra terms (photon-photon absorption on external photons) and solve numerically  for high τ, no limit cycle behavior.

Protons: injection Electrons: Photons: Neutrinos: Neutrons: Bethe-Heitler proton triplet ssa γγ annihilationphotopion synchrotron pair production FULL NUMERICAL CODE: A REMINDER

USING THE FULL NUMERICAL CODE photons protons time When all processes are included, the system retains its basic dynamical signatures found analytically.

PAIR PRODUCTION – SYNCHROTRON LOOP PROTONS  BETHE-HEITLER PAIRS | | | SYNCHROTRON PHOTONS |_______________|________ | escape Loop operational if two criteria, feedback and marginal stability, are simultaneously satisfied  protons supercritical  Pairs/photons exponentiate in the source n γ ~ n e ~ exp(st) supercritical regime Kirk & AM 1992 s=1 s=0 Feedback criterion Marginal stability criterion

THE STEP TO SUPERCRITICALITY SUPERCRITICAL REGIME B=10 GR=3e16 cm In all cases the proton injection luminosity is increased by 1.25  corresponding photons increase by several orders of magnitude SUBRCRITICAL REGIME I Time-dependent transition of photon spectra from the subcritical to the supercritical regime

A MAP OF PROTON SUPERCRITICALITIES quenching- πγ induced cascade PPS Loop quenching- BH induced cascade SUBCRITICAL REGIME B=10 GR=3e16 cm SUPERCRITICAL REGIME

CONCLUSIONS One-zone hadronic model –Accurate secondary injection (photopion + Bethe Heitler) –Time dependent - energy conserving PDE scheme Five non-linear PIDE – c.f. leptonic models have only two First results for pure hadronic injection - Low efficiencies - γ-rays steeper than neutrino spectra - Quadratic time-behaviour of radiation from secondaries (similar to synchrotron – SSC relation of leptonic models) - Inherently non-linear  applications (e.g. AGN variability?) - Strong supercriticalities exclude sections of parameter-space used for modeling AGNs