Advection-dominated Accretion:From Sgr A* to Other Low-Luminosity

AGNs

Feng Yuan (Shanghai Astronomical Observatory)

Collaborators: Ramesh Narayan; Eliot Quataert; Rodrigo Nemmen; Wei Cui; Zhiqiang Shen; Sera Markoff; Heino Falcke…

OutlineOutline

Sgr A* as a unique laboratory for Sgr A* as a unique laboratory for extremely low luminosity accretionextremely low luminosity accretion

ADAF models for other low-luminosity ADAF models for other low-luminosity AGNsAGNs

Complexity…Complexity…

Sgr A*: a Unique Laboratory for Low-Sgr A*: a Unique Laboratory for Low-Luminosity AccretionLuminosity Accretion

Best evidence for a BH (stellar orbits)Best evidence for a BH (stellar orbits)– M M 4x10 4x106 6 MM

Largest BH on the sky (horizon Largest BH on the sky (horizon 8 8 μμ""),), thus most detailed constraints on thus most detailed constraints on ambient conditions around BHambient conditions around BH

– Direct observational determinationDirect observational determination to the accretion rate to the accretion rate – Outer boundary conditionsOuter boundary conditions

Abundant observational data:Abundant observational data:– Detailed SEDDetailed SED– polarizationpolarization– X-ray & IR flares probe gas at ~ RX-ray & IR flares probe gas at ~ Rss

Accretion physics at extreme low luminosity (L ~ 10Accretion physics at extreme low luminosity (L ~ 10-9 -9 LLEDDEDD))Useful laboratory for other BH systemsUseful laboratory for other BH systems

Fuel SupplyFuel SupplyIR (VLT) image of central ~ pc Chandra image of central ~ 3 pc

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Hot x-ray emitting gas(T = 1-2 keV; n = 100 cm-3)

produced via shocked stellar winds

Young cluster of massive stars in the central ~ pc loses ~ 10-3

M yr-1 ( 2-10" from BH)

Outer Boundary Conditions at Outer Boundary Conditions at Bondi RadiusBondi Radius

Bondi radius:Bondi radius:

Mass accretion rate estimationMass accretion rate estimation

this is roughly consistent with the numerical simulation of Cuadra et al. this is roughly consistent with the numerical simulation of Cuadra et al.

(2006):(2006):

TemperatureTemperature: 2keV; : 2keV; DensityDensity: 130cm^-3: 130cm^-3

Angular momentum:Angular momentum: quite large, the circularization radius ~10^4 Rs, not quite large, the circularization radius ~10^4 Rs, not a spherical accretion (Cuadra’s talk)a spherical accretion (Cuadra’s talk)

152 10|4

yrMcRM

ARRsAcaptured

ss

A Rc

GMR 5"

2101

16.

103

yrMM

Observational Results for Sgr A* (I): Observational Results for Sgr A* (I): SpectrumSpectrum

flat radio spectrumflat radio spectrum

submm-bumpsubmm-bump

two X-ray statestwo X-ray states– quiescent: photon indx=2.2quiescent: photon indx=2.2

the source is resolvedthe source is resolved– flare: phton index=1.3flare: phton index=1.3

Total Luminosity ~ 1036 ergs s-1

~ 100 L ~ 10-9 LEDD ~ 10-6 M c2

Flare

Quiescence

KeckVLT

VLABIMASMA

Observational Results for Sgr A* Observational Results for Sgr A* (II): Variability & Polarization(II): Variability & Polarization

1.X-ray flare (Baganoff et al. 2001):1.X-ray flare (Baganoff et al. 2001): timescale: ~hour timescale (duration) ~10 min (shortest)timescale: ~hour timescale (duration) ~10 min (shortest)10Rs;10Rs; amplitude: can be ~45 amplitude: can be ~45 2.IR flare: timescale (Genzel et al 2003): : timescale (Genzel et al 2003):

~30-85 min (duration); ~5 min (shortest) ~30-85 min (duration); ~5 min (shortest) similar to X-ray flare similar to X-ray flare amplitude: 1-5, much smaller than X-rayamplitude: 1-5, much smaller than X-ray

3. Polarization: 3. Polarization: at cm wavelength: no LP but strong CP;at cm wavelength: no LP but strong CP; at submm-bump: high LP(7.2% at 230 GHz; <2% at at submm-bump: high LP(7.2% at 230 GHz; <2% at

112 112 GHz) GHz) a strict constraint to density & B field: a strict constraint to density & B field: RM (Faraday rotation measure) can not be too large RM (Faraday rotation measure) can not be too large (Aitken et al. 1999; Bower et al. 2003; Marrone et al. 2007; Zhao’s (Aitken et al. 1999; Bower et al. 2003; Marrone et al. 2007; Zhao’s

talk):talk): 255 m rad10)7.06.5(101.8

drrBnRM e

The Standard Thin Disk Ruled OutThe Standard Thin Disk Ruled Out

1. inferred low efficiency

2. where is the expected blackbody emission?

3. observed gas on ~ 1” scalesis primarily hot & spherical,not disk-like

4. absence of stellar eclipsesargues against >> 1 disk (Cuadra et al. 2003)

Radiation-hydrodynamics Equations Radiation-hydrodynamics Equations for ADAF(&RIAF)for ADAF(&RIAF)

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ieee

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s

out

out

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dp

dr

dv

qqqdr

dp

dr

dv

prjrv

dr

dpr

dr

dvv

R

RMvRHM

)1(

)(

1

4

2

2

2

22

..

Mass accretion rate:

The radial and azimuthal Components of the momentum Equations:

The electron energy equation:

The ions energy equation:

“old” ADAF: s=0; δ<<1“new” ADAF (RIAF): s>0; δ≤1

““Old” ADAF Model for Sgr A*Old” ADAF Model for Sgr A*Narayan et al., 1995;1998; Manmoto et al. 1997Narayan et al., 1995;1998; Manmoto et al. 1997

The “old” ADAF The “old” ADAF (e.g., Ichimaru 1977; Rees et al. 1982; Narayan & Yi 1994;1995; Abramowicz et al. 1995…)

– ADAF: most of the viscously dissipated energy is stored in the thermal ADAF: most of the viscously dissipated energy is stored in the thermal energy and advected into the hole rather than radiated away.energy and advected into the hole rather than radiated away.

– TTpp=10=101212K;TK;Tee=10=1099—10—101010K; K; geometrically thick geometrically thick

– Accretion rate = const.Accretion rate = const.– Efficiency<<0.1, because electron heating is inefficient (adiabatic)Efficiency<<0.1, because electron heating is inefficient (adiabatic)

Success of this ADAF model:Success of this ADAF model:– low luminosity of Sgr A*;low luminosity of Sgr A*;– rough fitting of SED; rough fitting of SED;

Problems of this ADAF model:Problems of this ADAF model:– predicted LP is too low because RM is too large;predicted LP is too low because RM is too large;– predicted radio flux is too low.predicted radio flux is too low.

Theoretical Developments of ADAFTheoretical Developments of ADAF

Outflow/convectionOutflow/convection Very little mass supplied at large Very little mass supplied at large

radii accretes into the black hole radii accretes into the black hole (outflows/convection suppress (outflows/convection suppress accretion: accretion: Narayan & Yi 1994; Blandford & Narayan & Yi 1994; Blandford & Begelman 1999; Narayan, Igumenshchev & Begelman 1999; Narayan, Igumenshchev &

Abramowicz 2000; Quataert & Gruzinov 2000Abramowicz 2000; Quataert & Gruzinov 2000))

Electron heating Electron heating mechanism: direct viscous mechanism: direct viscous heating?heating?

turbulent dissipation & magnetic turbulent dissipation & magnetic reconnectionreconnection

Particle distribution: Particle distribution: nonthermal?nonthermal?– weak shocks & magnetic weak shocks & magnetic

reconnectionreconnection– collisionless plasmacollisionless plasmanonthermal?nonthermal?

(Stone & Pringle 2001; Hawley & Balbus 2002; Igumenshchev et al. 2003)

MHD numerical simulation result:(however, collisionlesskinetic theory?)

5.0~

RIAF Model for the Quiescent StateRIAF Model for the Quiescent State

synchrotron emission from synchrotron emission from power-law electronspower-law electrons

synchrotron, bremsstrahlung synchrotron, bremsstrahlung

and their Comptonization from and their Comptonization from

thermal electronsthermal electrons

bremsstrahlung from the bremsstrahlung from the

transition region around the transition region around the

Bondi radiusBondi radius

total emission from both total emission from both thermal and power-law electronsthermal and power-law electrons

Yuan, Quataert & Narayan 2003

RIAF Model for Sgr A*: Interpreting the RIAF Model for Sgr A*: Interpreting the Polarization ResultPolarization Result

Yuan, Quataert & Narayan 2003

Summary: the efficiency of RIAF in Summary: the efficiency of RIAF in Sgr A*Sgr A*

Mdot ~ 10Mdot ~ 10-6 -6 MMsunsun/yr, L ~ 10/yr, L ~ 103636erg/s, so erg/s, so efficiency ~10efficiency ~10-6-6

In the “old” ADAF(no outflow), this low efficiency is due In the “old” ADAF(no outflow), this low efficiency is due to the inefficient electron heating (or ion energy to the inefficient electron heating (or ion energy advection)advection)

In the “new” ADAF (with outflow and ), In the “new” ADAF (with outflow and ),

MdotMdotBH BH ~ 10~ 10-8-8MMsunsun/yr, so /yr, so outflow contributes a factor of outflow contributes a factor of

0.010.01

The other factor of ~10The other factor of ~10-4-4 is due to electron energy is due to electron energy advectionadvection: the energy heating electrons is stored as their : the energy heating electrons is stored as their thermal energy rather than radiated away (electron thermal energy rather than radiated away (electron energy advection)energy advection)

5.0~

Understanding the IR & X-ray flaresUnderstanding the IR & X-ray flares of Sgr A*: Basic Scenarioof Sgr A*: Basic Scenario

At the time of flares, at the innermost region of accretion At the time of flares, at the innermost region of accretion flow, flow, ≤10R≤10Rss, , some transient events, such as magnetic some transient events, such as magnetic

reconnection (------solar flares!), occur.reconnection (------solar flares!), occur.

During this process, some fraction of thermal electrons will During this process, some fraction of thermal electrons will be heated & accelerated (reconnection current sheet? be heated & accelerated (reconnection current sheet? shock?)shock?)

The synchrotron & its inverse Compton emissions from The synchrotron & its inverse Compton emissions from these high-energy electrons can explain the IR & X-ray these high-energy electrons can explain the IR & X-ray flares detected in Sgr A*flares detected in Sgr A*

Yuan, Quataert & Narayan 2003; 2004; Yuan et al. 2007

Yuan, Shen, & Huang 2006, ApJ

7mm(up) & 3.5mm(lower) simulation results

Input intensity profile Simulation result Gaussian fit

7mm

3.5mm

Testing the RIAF Model with the Size MeasurementsTesting the RIAF Model with the Size Measurements

When the luminosity/accretion rate When the luminosity/accretion rate increases…...increases…...

Low-luminosity AGNs: ObservationsLow-luminosity AGNs: Observations

LLAGNs are very common, over 40% of nearby LLAGNs are very common, over 40% of nearby galaxies contain LLAGNs (Ho et al. 1997)galaxies contain LLAGNs (Ho et al. 1997)

LLbol bol / L/ LEddEdd ~ 10 ~ 10-5 -5 -- 10 -- 10-3-3

Given the available accretion rates, the Given the available accretion rates, the efficiency should be 1-4 orders of magnitude efficiency should be 1-4 orders of magnitude lower than 0.1 (Ho 2005)lower than 0.1 (Ho 2005)

Unusual SED: no BBBUnusual SED: no BBB

No broad iron K lineNo broad iron K line

Double-peaked H line Double-peaked H line R Rinin ~ (100-1000)R ~ (100-1000)Rs s

Average SED of Low-luminosity Average SED of Low-luminosity AGNsAGNs

Ho (1999)

Radio-loud AGNs

Radio-quiet AGNs

low-luminosity AGNs, no BBB!L

Current Accretion Scenario Current Accretion Scenario for Low-luminosity AGNsfor Low-luminosity AGNs

Jet: radio

Truncated standard thin disk:T~106Koptical&UV

ADAF: X-ray

Transition radius

The Transition RadiusThe Transition Radius

Two mechanisms for the Two mechanisms for the transition:transition:

Evaporation Evaporation (e.g.,Meyer & Meyer-

Hofmeister, 1994; Liu, Meyer & Meyer-Hofmeister, 1995; Liu et al. 1999; Rózanska & Czerny 2000)

Turbulent energy Turbulent energy transportation transportation

(e.g., Honma 1996; Manmoto (e.g., Honma 1996; Manmoto & Kato 2000)& Kato 2000)

Transition radius vs. luminosity; from Yuan & Narayan 2004

M 81M 81Quataert et al. 1999

Rtr ~ 100 Rs

NGC 1097: the best example?NGC 1097: the best example?

Double peaked Balmer line Rtr=225Rs, consistent with spectral fitting result!

From a truncated thin disk, with Rtr = 225 Rs

Nemmen et al. 2006

Hard state of black hole X-ray Hard state of black hole X-ray binary: XTE J1118-480binary: XTE J1118-480

Hard state of black hole X-ray Hard state of black hole X-ray binary is generally assumed binary is generally assumed to be the analogy of LLAGNs to be the analogy of LLAGNs or Seyfert galaxies.or Seyfert galaxies.The value of the transition The value of the transition radius is well determined by radius is well determined by the EUV data, Rthe EUV data, Rtrtr ~ 300 R ~ 300 Rss

A QPO of frequency 0.07---A QPO of frequency 0.07---0.15 Hz is detected 0.15 Hz is detected If we explain the QPO as the If we explain the QPO as the p-mode oscillation of the p-mode oscillation of the ADAF, this QPO frequency ADAF, this QPO frequency also suggests that the also suggests that the transition radius to be ~300 Rtransition radius to be ~300 Rss

Yuan, Cui & Narayan 2005

Radiation from the truncated thin disk, with Rtr = 300 Rs

Ellipticals: Fabian & Rees 1995Ellipticals: Fabian & Rees 1995

FRFRII: Reynolds et al 1996; Begelman & Celloti 2004; Wu, Yuan & Cao 2007: Reynolds et al 1996; Begelman & Celloti 2004; Wu, Yuan & Cao 2007

XBONGs: Yuan & Narayan 2004XBONGs: Yuan & Narayan 2004

Seyfert 1 galaxies: Chiang & Blaes 2003Seyfert 1 galaxies: Chiang & Blaes 2003

Blazar: Maraschi & Tavecchio 2003Blazar: Maraschi & Tavecchio 2003

Many questions remain unsolved:Many questions remain unsolved:

The X-ray emission from luminous sources such as quasar and the very The X-ray emission from luminous sources such as quasar and the very high state of X-ray binarieshigh state of X-ray binaries

The broad iron line detected in the hard state (if it is true)The broad iron line detected in the hard state (if it is true)

How to form a jetHow to form a jet

…………

Other examples include:

However:

One example of complexity: the role One example of complexity: the role of jet in LLAGNsof jet in LLAGNs

It is almost certain the radio It is almost certain the radio emission comes from jets; but emission comes from jets; but it is possible thatit is possible that for some for some sources jets also dominate the sources jets also dominate the emission at other wavebands.emission at other wavebands.One example: NGC 4258One example: NGC 4258– The IR spectrum and the The IR spectrum and the

mass accretion rate seem to mass accretion rate seem to be hard to explain by an ADAF be hard to explain by an ADAF

– A jet can interpret the A jet can interpret the spectrum ifspectrum if

a significant fraction of a significant fraction of accretion flow is transferred accretion flow is transferred into the jet; and into the jet; and the underlying accretion flow the underlying accretion flow is described by an ADAF.is described by an ADAF. Yuan, Markoff, Falcke & Biermann 2002

Thank you!Thank you!