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
Ge
nze
l et a
l.
Ba
ga
no
ff et a
l.
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)
ieii
ieee
k
s
out
out
qqdr
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!
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