particleacceleration and the quiescent and flare emissions in sgr … · 2009. 5. 13. ·...

Particle Acceleration and the Quiescent and Flare Emissions in

Sgr A* (and other AGNs?)

In collaboration with

Siming Liu, Alex Lazarian, Fulvio Melia and graduate students

Huatulco, April 2007

Astro-ph 0403487, 0506151, 0603136 and 137

2

Outline

Accretion in Black Holes Observations of Sgr A*Emission MechanismsStochastic Acceleration

Quiescent mm and X-ray EmissionNIR and X-ray Flares

Radio and TeV Emission

3

Accretion in Black Holes

Optically Thick Optically ThinHigh Density Low Density

Thermal Equilibrium Collisionless Plasma?

High Efficiency Low Efficiency

Cold Hot

Geometrically Thin Geometrically Thick

Luminosity ~Ledd Luminosity

4

Accretion in Black Holes

Muller 2004

6

Some Basic Parameters for Black Hole in Sgr A*

• Distance • Black Hole Mass• Eddington Luminosity• Schwarzschild Radius• Angular size • Timescales:

sunBH MM6104×≈

cm 102.1 12×=sr

arcsec10/ 5−== Drssϑ

kpc 8≈D

sec )/(400

sec )/(402/3

sKep

ss

rR

rR

≈

=

τ

τ

erg/s 1045≈EDDL

7

Gravitational Energy Release of Protons and Ions

Generation of Turbulence via Instabilities

Electron Acceleration by the Turbulence

Radiation Produced by Electrons and Protons

Energy Flow

8

Accretion Flow in Kerr Black Holes

De Villiers et al. 2003 ApJ

gasmag PP /

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Observation of

Sagittarius A*

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Radio Observations, VLA

Lo et al. 1998, ApJ, 508, 61

11(From Zhao et al.

2004)

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X-ray Flares from Sgr A*(Baganoff et al. 2001)

In flare-state, Sgr A*’s X-ray luminosity can increase by more than one order of magnitude.

The X-ray flare lasted for a few hours. Significant variation in flux was seen over a 10 minute interval.

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NIR Flares From Sgr A*Quasi-periodic Modulation

Genzel et al. 2003

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Sgr A* June 2003, NIR/X-ray Flare

Eckart et al. (2004)

Baganoff 2005

erg/s 10 while

erg/s 105 erg/s, 10645

3433

≈

×≈×≈−

EDD

NIRrayX

L

LL

15

HESS

H.E.S.S. Preliminary

HESS Collaboration 2004

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Emission Mechanisms

in

Sagittarius A*

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Broadband Spectrum

ergs/s 1036=ννL

ergs/s 1033=ννL

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Soft NIR Flares

Hard X-ray Flares

Broadband Spectrum

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Emission Mechanisms in General“Thermal” Synchrotron and SSC:

Four Parametersn, B, kBT = γcrmec2, R

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“Thermal” Synchrotron Spectrum

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Thermal Synchrotron and SSCDetails

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Emission Processes During Flares

Thermal Synchrotron

and SSC:

N=3.8x1042kBT=75mec2

Liu et al. 2006

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Emission Mechanism for the TeV SourceSynchrotron Self-Compton

Atoyan and Dermer 2004, ApJ, 617, 123

B=90μG

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Emission Mechanism for the TeV SourcePhoto-Meson Interactions

Aharonian et al 2005, ApJ, 619, 306

E>1018eV

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Emission Mechanism for the TeV SourceProton-Proton Interactions

Aharonian et al 2005, ApJ, 619, 306; Liu et al. 2006

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PARTICLE ACCELERATION

in

Galactic Center Quiescent and Flare Sources

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ACCELERATION MECHANISMSGeneral

A: Electric Fields: Parallel to B Field Parallel to B Field Unstable leads to TURBULENCE

B: Fermi Acceleration1. Shock or Flow Divergence: First Order First Order

Shocks and Scaterers; i.e. TURBULENCE2. Stochastic Acceleration: Second OrderSecond OrderScattering and Acceleration by TURBULENCE

TURBULENCE

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PLASMA TURBULENCE AND STOCHASTIC ACCELERATION

1. GenerationMagneto-RotationalInstability (MRI)

,1/ >>= νLVeR 1 / >>= ηLVRm

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1. Generation2. Cascade: Nonlinear wave-wave int.

,1/ >>>= νLVeR 1 / >>>= ηLVRm

321321 ;)()()( kkkkkk =+=+ ωωω

30


1. Generation 2. Cascade: Nonlinear wave-wave int.

3. Interactions with Particles: Resonant int.

,1/ >>>= νLVeR 1 / >>>= ηLVRm

321321 ;)()()( kkkkkk =+=+ ωωω

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Wave-Particle Interactions

• Dominated by Resonant Interactions

• Lower energy particles interacting with higher wavevectors or frequencies

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2. PLASMA TURBULENCE AND STOCHASTIC ACCELERATION

1. Generation (MRI)2. Cascade: Nonlinear wave-wave int.

3. Interactions with Particles: Resonant int.

A. Damping of WavesB. Acceleration of Particles

,1/ >>>= νLVeR 1 / >>>= ηLVRm

321321 ;)()()( kkkkkk =+=+ ωωω

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kmin

kmax

k-q

k-q’

Turbulence Spectrum

2007-5-7 34

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Model Parameters

In principle: Density nTemperature TMagnetic Field BScale (geometry) RLevel of Turbulence

or 2)/( BBδ 2)/( Alfvenvvδ

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Kinetic Equation Coefficients

Acceleration rate or time:Loss rate or time:Escape rate or time:Characteristic Times:

acτ

escT

lossτ

vRTBB crossep 2/ and )/(21 ≈Ω∝− δτ

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EXAMPLES OFTimescales And Spectra For 3 Models

Alfven Velocity

1.0/ =cvA

38

Electron Acceleration

During

NIR and X-ray Flares

39

Submm, NIR and X-rays from the Disk


gasmag PP /

40

Stochastic Electron Acceleration

41


Maxiwellian

Without injection:Continuousheating andcooling

InjectionContinuousinjection, heating, &cooling.

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Acceleration Scenario for Flares

Simplify the model: Simpler Kinetic Equation

Parametric approach:

One less parameter: 1)/( 2 ≈= BBfturb δ

Synchturbac LL ≈= const., τ

43


44

Emission by Accelerated Electrons

45

Summary-I• Flares from Sgr A* are produced near the event

horizon of the black hole• NIR and X-ray emissions are produced via

thermal synchrotron and SSC by energetic electrons accelerated by plasma waves.

• The observed NIR or X-ray fluxes and spectral indexes can be used to measure B, R, n, and T, which will result in a better understanding of the flare energizing mechanism and may lead to a measurement of the black hole spin.

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LARGE SCALE EMISSIONS

Long Wavelength RadioEscaping Electrons

TeV gamma-raysEscaping protons

Acceleration and Emission in the Jet

47

Acceleration within 20rS

48

Long Wave Radio and TeV Emissionfrom the escaping particles in the JET


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Stochastic Acceleration ofElectrons and Protons

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Proton Acceleration

Cooling is too efficientto produce 7mm emission

Source is too bright in the radioband.

Source is optically thin at 7mm

52

The TeV source is likely produced via pp scatterings by protons accelerated near the black hole and diffusing toward large radii.

Should the 7mm emission be produced by electrons in the acceleration region, the acceleration region must be strongly magnetized and far from equipartition.

Summary-II

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Structure of the Accretion Flow


Sub-mm, NIR, and X-ray via Synchrotron and SSC

cm and mm via Synchrotron and proton acceleration

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Conclusions

In combination with the theory of Stochastic Acceleration by plasma

waves and MHD simulations, observations over a broad energy range can be used to detect the

properties of the black hole and its accretion flows.

55

Example

56

Example

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ImplicationsThermal Synchrotron Sources

Can be generalized to Comptonization dominant sourcese.g., X-ray binaries, to address the coupling of electrons

and protons via turbulence

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Constraining C1 and C2

Fν=12mJyFx = 0.22µJy

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TIMESCALES

Particle Acceleration and the Quiescent and Flare Emissions in � Sgr A* (and other AGNs?) OutlineAccretion in Black HolesAccretion in Black HolesSome Basic Parameters for Black Hole in Sgr A*Energy Flow Accretion Flow in Kerr Black Holes�NIR Flares From Sgr A*Sgr A* June 2003, NIR/X-ray FlareEmission Mechanisms in General“Thermal” Synchrotron SpectrumThermal Synchrotron and SSC�DetailsEmission Processes During FlaresEmission Mechanism for the TeV Source�Synchrotron Self-ComptonEmission Mechanism for the TeV Source �Proton-Proton Interactions ACCELERATION MECHANISMS�General PLASMA TURBULENCE AND STOCHASTIC ACCELERATION PLASMA TURBULENCE AND STOCHASTIC ACCELERATION PLASMA TURBULENCE AND STOCHASTIC ACCELERATION Wave-Particle Interactions2. PLASMA TURBULENCE AND STOCHASTIC ACCELERATIONModel Parameters Kinetic Equation CoefficientsEXAMPLES OF� Timescales And Spectra For 3 ModelsSubmm, NIR and X-rays from the Disk�Stochastic Electron AccelerationStochastic Electron AccelerationAcceleration Scenario for FlaresStochastic Electron AccelerationEmission by Accelerated ElectronsSummary-ILARGE SCALE EMISSIONSLong Wave Radio and TeV Emission from the escaping particles in the JETStochastic Acceleration of�Electrons and ProtonsProton AccelerationThe TeV source is likely produced via pp scatterings by protons accelerated near the black hole and diffusing toward large radStructure of the Accretion FlowConclusionsExampleExampleImplicationsTIMESCALES

particleacceleration and the quiescent and flare emissions in sgr … · 2009. 5. 13. ·...

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