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
5
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 /
9
Observation of
Sagittarius A*
10
Radio Observations, VLA
Lo et al. 1998, ApJ, 508, 61
11(From Zhao et al.
2004)
12
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.
13
NIR Flares From Sgr A*Quasi-periodic Modulation
Genzel et al. 2003
14
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
16
Emission Mechanisms
in
Sagittarius A*
17
Broadband Spectrum
ergs/s 1036=ννL
ergs/s 1033=ννL
18
Soft NIR Flares
Hard X-ray Flares
Broadband Spectrum
19
Emission Mechanisms in General“Thermal” Synchrotron and SSC:
Four Parametersn, B, kBT = γcrmec2, R
20
“Thermal” Synchrotron Spectrum
21
Thermal Synchrotron and SSCDetails
22
Emission Processes During Flares
Thermal Synchrotron
and SSC:
N=3.8x1042kBT=75mec2
Liu et al. 2006
23
Emission Mechanism for the TeV SourceSynchrotron Self-Compton
Atoyan and Dermer 2004, ApJ, 617, 123
B=90μG
24
Emission Mechanism for the TeV SourcePhoto-Meson Interactions
Aharonian et al 2005, ApJ, 619, 306
E>1018eV
25
Emission Mechanism for the TeV SourceProton-Proton Interactions
Aharonian et al 2005, ApJ, 619, 306; Liu et al. 2006
26
PARTICLE ACCELERATION
in
Galactic Center Quiescent and Flare Sources
27
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
28
PLASMA TURBULENCE AND STOCHASTIC ACCELERATION
1. GenerationMagneto-RotationalInstability (MRI)
,1/ >>= νLVeR 1 / >>= ηLVRm
29
PLASMA TURBULENCE AND STOCHASTIC ACCELERATION
1. Generation2. Cascade: Nonlinear wave-wave int.
,1/ >>>= νLVeR 1 / >>>= ηLVRm
321321 ;)()()( kkkkkk =+=+ ωωω
30
PLASMA TURBULENCE AND STOCHASTIC ACCELERATION
1. Generation 2. Cascade: Nonlinear wave-wave int.
3. Interactions with Particles: Resonant int.
,1/ >>>= νLVeR 1 / >>>= ηLVRm
321321 ;)()()( kkkkkk =+=+ ωωω
31
Wave-Particle Interactions
• Dominated by Resonant Interactions
• Lower energy particles interacting with higher wavevectors or frequencies
32
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
33
kmin
kmax
k-q
k-q’
Turbulence Spectrum
2007-5-7 34
35
Model Parameters
In principle: Density nTemperature TMagnetic Field BScale (geometry) RLevel of Turbulence
or 2)/( BBδ 2)/( Alfvenvvδ
36
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
37
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
De Villiers et al. 2003 ApJ
gasmag PP /
40
Stochastic Electron Acceleration
41
Stochastic Electron Acceleration
Maxiwellian
Without injection:Continuousheating andcooling
InjectionContinuousinjection, heating, &cooling.
42
Acceleration Scenario for Flares
Simplify the model: Simpler Kinetic Equation
Parametric approach:
One less parameter: 1)/( 2 ≈= BBfturb δ
Synchturbac LL ≈= const., τ
43
Stochastic Electron Acceleration
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.
46
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
De Villiers et al. 2003 ApJ
49
50
Stochastic Acceleration ofElectrons and Protons
51
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
53
Structure of the Accretion Flow
De Villiers et al. 2003 ApJ
Sub-mm, NIR, and X-ray via Synchrotron and SSC
cm and mm via Synchrotron and proton acceleration
54
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
57
ImplicationsThermal Synchrotron Sources
Can be generalized to Comptonization dominant sourcese.g., X-ray binaries, to address the coupling of electrons
and protons via turbulence
58
Constraining C1 and C2
Fν=12mJyFx = 0.22µJy
59
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
Top Related