the hadronic model of active galactic nuclei a. mastichiadis university of athens
Post on 19-Dec-2015
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TRANSCRIPT
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-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 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.
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 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)
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