THE HADRONIC MODELOF 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 detector2nd 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-field soft photons

inverse comptonsynchrotron

Active Region aka The Blob:

Relativistic Electrons

INTERACTIONS OF PROTONS WITH PHOTON FIELDS

photopair production

photomeson production

photopair

photomesonLoss tim

escale

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 protoninduced radiationmechanisms

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 RAYSAND 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, γp, Lp)

AIMS1. 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 LOSSESPROTON ESCAPE

ELECTRONS-POSITRONS

PHOTONS

OBSERVED SPECTRUM

Leptonic processes

Protons:

injection

Electrons:

Photons:

Neutrinos:

Neutrons:

Bethe-Heitler

proton

triplet

ssa

γγ

annihilationphotopion

synchrotron

synchrotron

pair production

INJECTION OF SECONDARΥ ELECTRONS -RESULTING PHOTON SPECTRA

Bethe-Heitler electrons

photopion electrons

γγ electrons

R = 3e16 cmB = 1 G

γp = 2e6lp = 0.4

electrons photons

S. Dimitrakoudis et al., in preparation

PHOTON AND NEUTRINO SPECTRA

Power law proton injection

injectedprotons

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 cmB = 1 G lp = 0.4

γp = 3e5 γp = 3e6 γp = 3e7

INCREASING THE PROTON INJECTED LUMINOSITY

log lp

B=1 G

Proton injected luminosity is increased by a factor 3

linearquadratic linear

quadratic

onset of supercriticality

R=3e16 cmhighly non-linear

AUTOMATIC PHOTON QUENCHINGStawarz & Kirk 2007Petropoulou & AM 2011

Injected gamma-ray luminosityE

scaping lum

inosity

gamma-rays

soft photons

Gamma-rays can be self-quenched:Non-linear network of• photon-photon annihilation• electron synchrotron radiationOperates independently of soft photonsPoses a strong limit on the gamma-ray luminosity of a source

quenched gamma-rays

‘reprocessed’ gamma-rays

--------------.lγ,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-rayquenchingregime

γ-rayquenchingregime

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- Protons np

- Hard photons nh

- Soft photons ns

assumed to be monoenergetic

• Parameters of the problem- Proton injection rate Q0

- Proton escape timescale τp

- Distribution of external photons nex

nex is needed to start photomeson reactionsand it is independent of time

Petropoulou & AM 2012

SIMPLIFIED EQUATIONS

injection

escape

photomeson losseson external photons

injection due to photomeson on external photons

photomeson losseson 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)

quenchingabsorption 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 cyclebehaviour to damped oscillationsto 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

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 basicdynamical signatures found analytically.

THE STEP TO SUPERCRITICALITY

SUPERCRITICALREGIME

B=10 G R=3e16 cm

In all cases the proton injectionluminosity is increased by 1.25 corresponding photons increase by several orders of magnitude

SUBRCRITICALREGIME

I

Time-dependent transition of photon spectra from the subcritical to the supercritical regime

A MAP OF PROTON SUPERCRITICALITIES

quenching-πγ inducedcascade

PPS Loop

quenching-BH inducedcascade

SUBCRITICAL REGIME

B=10 G R=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