Accretion flows II

Accretion flows II

This lecture is part of the course "physics of active galactic nuclei" offered to graduate students in astrophysics by Rodrigo Nemmen and Joao Steiner at IAG USP.


Rodrigo Nemmen

May 20, 2016


  1. 5.
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    Frank et al. Family of solutions for the Bondi accretion

    problem winds winds accretion extended atmosphere
  4. 12.

    Frank et al. Family of solutions for the Bondi accretion

    problem accretion solution we are looking for gas in free- fall for r < rs
  5. 14.

    Application of Bondi formalism to an early type galaxy: M87

    Russell et al. 2013, MNRAS ˙ M Bondi ⇠ 0.4 M yr 1 R Bondi ⇠ 42 pc
  6. 15.

    1506.02591v1 [astro-ph.GA] 8 Jun 2015 Mon. Not. R. Astron. Soc.

    000, 1–10 (2012) Printed 9 June 2015 (MN L A TEX style file v2.2) Bondi-Hoyle-Littleton accretion and the upper mass stellar IMF Javier Ballesteros-Paredes1 ∗, Lee W. Hartmann2, Nadia P´ erez-Goytia1, and Aleksandra Kuznetsova2 1 Centro de Radioastronom´ ıa y Astrof´ ısica, Universidad Nacional Aut´ onoma de M´ exico, Apdo. Postal 72-3 (Xangari), Morelia, Michoc´ an 58089, M´ exico 2 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105, USA Submitted to MNRAS, 9 June 2015 ABSTRACT We report on a series of numerical simulations of gas clouds with self-gravity forming sink particles, adopting an isothermal equation of state to isolate the effects of gravity from thermal physics on the resulting sink mass distributions. Simulations starting with supersonic velocity fluctuations develop sink mass functions with a high-mass power-law tail dN/d log M ∝ MΓ, Γ = −1 ± 0.1, independent of the initial Mach number of the velocity field. Similar results but with weaker statistical significance hold for a simulation starting with initial density fluctuations. This mass function power-law dependence agrees with the asymptotic limit found by Zinnecker assuming Bondi-Hoyle-Littleton (BHL) accretion, even though the mass accretion rates of indi- vidual sinks show significant departures from the predicted ˙ M ∝ M2 behavior. While BHL accretion is not strictly applicable due to the complexity of the environment, we argue that the final mass functions are the result of a relative M2 dependence result- ing from gravitationally-focused accretion. Our simulations may show the power-law mass function particularly clearly compared with others because our adoption of an isothermal equation of state limits the effects of thermal physics in producing a broad initial fragmentation spectrum; Γ → −1 is an asymptotic limit found only when sink
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    Radiative efficiency = 6 - 42% 0.01 & L/LEdd &

    0.3 Thin accretion disks H/R ⇠ 0.01
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    these collisions is that angular momentum is transferred to the outer reaches of the disk while the gas whirls inward to the central star or black hole. Material in the inner parts of an accretion disk takes less time to complete an orbit than does material in the outer parts (right). Bits of material that are closer to the center of the disk slide past material that is slightly farther out. In an accretion disk around a star or black hole, large-scale blobs of gas collide violently in a turbulent flow (bottom). This process transports angular momentum outward, causing some of the gas to lose rotational support and spiral inward (far right). And because the collisions make the material very hot, the disk radiates large amounts of visible, ultraviolet and x-ray radiation. Two blobs of gas in slightly different orbits collide with each other because the inner blob is moving a bit faster than the outer one. The collision transfers energy and angular momentum from the inner to the outer blob. The heated gas generates radiation. Deprived of energy, the inner blob falls to a closer orbit and gains speed. The outer blob is flung to a farther orbit, slowing it down. Rotational velocity Inner blob Outer blob Radiation New path of inner blob New path of outer blob Angular momentum Mass transport Blaes 03, Sci. Am.
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    “ISCO” Basic parameters of accretion disk rin rout limited by

    self-gravity ˙ M Disk as seen from above
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    “ISCO” Basic parameters of accretion disk rin rout limited by

    self-gravity ˙ M Disk as seen from above
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    20 40 60 80 100 r/rg 50000 100000 150000 200000

    250000 300000 T[K] Temperature of thin disks around supermassive black holes maximally spinning no spin M = 108M ˙ M = 0.1 ˙ MEdd
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    Temperature of thin disks around supermassive black holes maximally spinning

    no spin M = 108M ˙ M = 0.1 ˙ MEdd 20 40 60 80 100 r/rg 5.0×106 1.0×107 1.5×107 T[K]
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    SEDs of thin accretion disks in AGNs peak in the

    ultraviolet 11 12 13 14 15 16 17 18 log ν [Hz] 40 41 42 43 44 45 46 log νLν [erg/s] M = 108M ˙ M = 0.1 ˙ MEdd Rin = 3RS
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    Quasar SEDs Shang, …, Nemmen et al. (2011) Thin disk

    model Nemmen & Brotherton (2010) Radio-loud Radio-quiet SEDs of thin accretion disks in AGNs peak in the ultraviolet: BIG BLUE BUMP
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    Two schematic disk–corona structu and the scattering geometry of the

    di ccretion disks Possible source of X-rays in luminous AGNs: Hot corona of electrons (similar to the Sun) Netzer
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    56 Accretion disks .1 1 10 100 1000 10000 105

    .01 .1 1 10 100 1000 Energy (eV) F ν ν1/3 ν2 hot corona thin disk Figure 4.3. A schematic of a combined disk–corona spectrum. The maximum Schematic spectrum of thin disk (T < 105 K) + hot corona (T = 108 K) Netzer
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    Radiative efficiency = 6 - 42% 0.01 & L/LEdd &

    0.3 Thin accretion disks H/R ⇠ 0.01 explain luminous AGNs (quasars and bright Seyferts) and stellar- mass black holes in high/soft state 11 12 13 14 15 16 17 18 log ν [Hz] 40 41 42 43 44 45 46 log νLν [erg/s] T < 105 K (peak in UV) ⌧ ⇠ 1
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    Fig. 9.—Snapshot of velocity streamlines in model A in meridional

    cross Fig. 10.—Same No. 2, 2003 RADIATIVELY INEFFICIENT ACCRETIO Turbulence in an accretion flow Igumenshchev et al. 2003, ApJ H
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    LETTERS Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical

    disks Hantao Ji1, Michael Burin1{, Ethan Schartman1 & Jeremy Goodman1 The most efficient energy sources known in the Universe are accre- tion disks. Those around black holes convert 5–40 per cent of rest- mass energy to radiation. Like water circling a drain, inflowing mass must lose angular momentum, presumably by vigorous tur- bulence in disks, which are essentially inviscid1. The origin of the turbulence is unclear. Hot disks of electrically conducting plasma can become turbulent by way of the linear magnetorotational instability2. Cool disks, such as the planet-forming disks of proto- stars, may be too poorly ionized for the magnetorotational instab- ility to occur, and therefore essentially unmagnetized and linearly stable. Nonlinear hydrodynamic instability often occurs in line- arly stable flows (for example, pipe flows) at sufficiently large Reynolds numbers. Although planet-forming disks have extreme Reynolds numbers, keplerian rotation enhances their linear hydrodynamic stability, so the question of whether they can be turbulent and thereby transport angular momentum effectively is controversial3–15. Here we report a laboratory experiment, dem- onstrating that non-magnetic quasi-keplerian flows at Reynolds numbers up to millions are essentially steady. Scaled to accretion Outer cylinder Inner cylinder Outer rings Shafts Pulley Seal holders Inner rings Fluid Vol 444|16 November 2006|doi:10.1038/nature05323
  24. 49.

    Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders

    M. S. Paoletti1 and D. P. Lathrop1,2,* 1Departments of Physics and Geology, Institute for Research in Electronics and Applied Physics, College Park, Maryland 20742, USA 2Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA (Received 27 September 2010; published 10 January 2011) We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the ( 1 , 2 ) parameter space at high Reynolds numbers, where 1 ( 2 ) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro ¼ ð 1 À 2 Þ= 2 fully determines the state and torque G as compared to GðRo ¼ 1Þ  G1. The ratio G=G1 is a linear function of RoÀ1 in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)]. DOI: 10.1103/PhysRevLett.106.024501 PACS numbers: 47.27.NÀ, 47.27.Jv, 47.32.Ef, 52.72.+v Rapidly rotating shear flows are ubiquitous in geophysi- cal and astrophysical settings such as planetary atmos- pheres, stellar interiors, and accretion disks. In order for essential fundamental processes to occur, like matter inflow towards compact objects [1], there must be an exchange of angular momentum through such flows. Determining the flux of angular momentum in rotating shear flows is difficult and has been actively studied [2–9] since the initial measurements of Wendt [10] and Taylor [11]. While shear tends to destabilize fluid flows, rotation stabilizes them whenever angular momentum in- creases radially outward (dL=dr > 0, the Rayleigh crite- rion [12]); however, shear turbulence can occur even in Rayleigh-stable systems [13]. Most astrophysical flows are Rayleigh stable, which in the absence of other instabilities were indistinguishable from those in solid-body rotation ( 1 ¼ 2 ), where the flux is zero. Ji et al. concluded that there was no hydrodynamic instability and that nonmag- netic, quasi-Keplerian flows at Reynolds numbers up to 2 Â 106 are ‘‘essentially steady.’’ These results are at odds with the analysis of Dubrulle et al. [6], who used prior velocity measurements to infer that the flux of angular momentum is nonzero for Rayleigh-stable flows. How- ever, there has yet to be a study that directly measures the flux of angular momentum in all portions of the ( 1 , 2 ) parameter space. Furthermore, Ji et al. could not quantify the flux for quasi-Keplerian flows since the random errors in their measurements exceeded the mea- sured values. In this Letter, we characterize the flux of angular mo- PRL 106, 024501 (2011) P H Y S I C A L R E V I E W L E T T E R S week ending 14 JANUARY 2011
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    Magnetorotational instability (MRI) First studied by Chandrasekhar 1963, Velikhov 1959

    But only in 1991 Balbus & Hawley realized their importance and generality 1991ApJ...376..214B >2350 citations as of Jun 2015
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    MRI in 3D I In reality, a magnetic field takes

    the place of a spring Magnetorotational instability (MRI) in 3D I In reality, a magnetic field takes the place of a spring Nick Murphy
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    I Where do reconnection & dynamo show up in this?

    Nick Murphy Corona Winds/ jets
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    Most Relevant Time Scales 28 Light-Crossing: 6 M8 ξ3 days

    Dynamical: 6 M8 ξ3 3/2 months Thermal: 5 α–1 –1 M8 ξ3 3/2 years Sound-Crossing: 70 M8 ξ3 T5 –1/2 years Viscous: 106 α–1 –4/5 M8 3/2 ξ3 5/4 m–1 –3/10 years Slide: Mike Eracleous (Penn State)
  29. 60.

    Strong cosmological evolution of quasar density: falls by a factor

    of ~100 from z~2 to z=0 13.7 Gyear 3.3 Gyear 1.2 Gyear Age of the universe Osmer 04, Silverman+05 redshift z number density (Mpc-3)
  30. 61.

    Most massive black holes at the centers of nearby galaxies

    are very faint SciAm M81 HST+Chandra+GALEX NGC 1097 quasars At z~0, >1000x less luminous than distant quasars
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    Most AGNs in the present-day universe are low- luminosity AGNs

    (LLAGNs): “LINERs” are the majority Palomar spectroscopic survey ~500 nearby galaxies (Ho+ 97, Nagar+ 05, Ho 08, 09) LINERs are extremely sub- Eddington systems: (Ho 09) hL bol i ⇠ 1040 1041 erg s 1 On average, >1000x less luminous than quasars:
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    What is going on in the centers of nearby galaxies?

    “The riddles of the sleeping monsters”
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    1) Nearby galactic nuclei are extremely underluminous given their large

    gas reservoirs ˙ M ⇠ 10 4 0.01 M yr 1 Black hole gas supply = Diffuse gas (Bondi accretion) + Mass-loss from evolved stars Assuming : L bol & 1042 erg s 1 rad ⌘ L ˙ Mc2 ⇠ 10% → They should be at least 10x as bright
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    Implication: ⌘rad ⌧ 10% Ho 08, 09 ˙ M ⇠

    10 4 0.01 M yr 1 Black hole gas supply = Diffuse gas (Bondi accretion) + Mass-loss from evolved stars Assuming : L bol & 1042 erg s 1 rad ⌘ L ˙ Mc2 ⇠ 10% → 1) Nearby galactic nuclei are extremely underluminous given their large gas reservoirs
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    Are all MBHs accreting and shining as AGN? No. Many

    MBHs are quiescent. We have an example is in the center of the Milky Way. The typical luminosity coming from the very center, Sgr A*, is ~1034 erg/s. Not much more than the Sun. Slides courtesy of Marta Volonteri (IAP) Brera 2013
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    Zoom in a little (2 degrees) Easier to see into

    center if you don’t have dust extinction M. Volonteri, Brera 2013
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    Sgr A* quiescent Chandra observations 105 rs , where rs

    = schild radius. The cally has an unab- (Lx ) of a few times ∼1011 lower than ed (Eddington) lu- enting a common uclei in the local mity, Sgr A* allows w-Lx state in un- eeds off the winds s (6–8). At the so- “normal” active galactic nucleus applies, one would predict a luminosity of Lx ∼ 1041 erg s−1. That the observed Lx is nearly a factor of ∼108 smaller has led to a renaissance of radiatively inefficient accretion flow (RIAF) models (10, 11), including self-similar solutions (12–17) and nu- merous hydrodynamic or magneto-hydrodynamic rescence of photospheric weakly ionized irons, irradiated by coronal flare x-rays. It is thus es- sential to test this hypothesis before we can as- sign the x-ray emission to the accretion flow onto the SMBH. We use data taken during the Sgr A* X-ray Visionary Program [XVP; (26)]. The Advanced Cambridge, Madingley artment of Astronomy, MA 01003, USA. 3Kavli esearch, Massachusetts A 02139, USA. 4Astro- niversity of Amsterdam, etherlands.5Department of Leicester, Leicester l Observatory, Chinese ad, Shanghai 200030, ia Universidad Católica ics Center and Depart- alifornia, Berkeley, CA nomique de Strasbourg, 550, Strasbourg, France. linary Exploration and of Physics and Astron- IL 60208, USA. 11Purple my of Sciences, Nanjing, chool of Astronomy and njing, 210093, China. oston, MA 02215, USA. ronomy, University of 2421, USA. Fig. 1. X-ray images of Sgr A* in quiescence. (A) An image constructed with the XVP 0th-order ACIS-S/HETG data in the 1- to 9-keV band. The contours are at 1.3, 2.2, 3.7, 6.3, and 11 × 10−4 counts s−1 arc sec−2. North is up and east is to the left. The dashed circle around Sgr A* marks its Bondi capture radius (assumed to be 4″). (B) A magnified image of Sgr A*. The emission is decomposed into extended (color image) and pointlike (contour) components. The latter component is modeled with the net flare emission (26) and is illustrated as the intensity contours at 0.3, 0.6, 1.2, 2.4, and 5 counts per pixel. The straight dashed line marks the orientation of the Galactic plane, whereas the dashed ellipse of a 1.5″ semimajor axis illustrates the elongation of the primary massive stellar disk, which has an inclination of i ∼ 127°, a line-of-nodes position angle of 100° (east from north), and a radial density distribution º r−2 with a ′′ Downloaded from 4’’ 1’’ Q.D. Wang+13, Science 2) Look at the center of Our Galaxy — Sagittarius A* is such a sleepy monster! Black hole gravitational sphere of influence Given the gas inflow rate, it should be 105 brighter assuming 10% radiative efficiency
  38. 72.

    Feng Yuan and Ramesh Naray 8 10 12 14 16

    18 20 log[ν(Hz)] 30 31 32 33 34 35 36 37 log[νL ν (erg s-1 )] Sgr A* Yuan+03, ApJ 2) Look at the center of Our Galaxy — Sagittarius A* is such a sleepy monster!
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    Quasar SEDs Shang, …, Nemmen et al. (2011) Thin disk

    model Nemmen & Brotherton (2010) Radio-loud Radio-quiet SEDs of thin accretion disks in AGNs peak in the ultraviolet: BIG BLUE BUMP
  40. 75.

    3) Weak AGNs have peculiar SEDs: lack of quasar UV

    excess (“big blue bump”) 〈LLAGN SED〉based on Eracleous+ 10
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    ? 3) Weak AGNs have peculiar SEDs: lack of quasar

    UV excess (“big blue bump”)
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    M87 Hercules A M84 4) AGNs come in two flavors:

    radio loud (jets) and radio quiet. Thin accretion disks are not good at producing jets. Multiple accretion modes?
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    1 5) In several LINERs, the Balmer and Fe Kα

    emission lines suggest that the thin disk is absent or “truncated” NGC 1097 - CTIO (SB, Nemmen+03) R in ~ 100 – 1000 GM/c2 ? ? ? ? NGC 3998 - XMM (Ptak+04) Lack of Fe Kα line @ 6.4 keV Energy (keV)
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    Low density gas t cool ≫ t acr Low accretion

    rates 1977, Rees et al. 1982, Narayan & Yi 1994, 1995 Kato et al. 2008, Narayan et al. 1998, Quataer & McClintock 2008 que abordam diferentes a escoamento acretivo no qual a maior parte da cosa permanece armazenada no g´ as e n˜ ao ´ e ir definidos pela condi¸ c˜ ao ADAF : qadv ≈ q+ ≫ q−, L Os ADAFs ocorrem para baixas taxas de acre¸ c 1.6), o que corresponde a baixas densidades j ´ e opticamente fino e tˆ enue, de forma que tcoo resfriamento e tacr ´ e a escala de tempo que o g´ a capaz de irradiar eficientemente e a eficiˆ encia ra e- ions Coulomb collisions
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    Optically thin (low densities) Low accretion rates Very hot T

    i ~ 1012 (R S /R) K T e ~ 109 - 1011 K Low radiative efficiency Underfed black holes are weird accretors: radiatively inefficient accretion flows SMBHs spend >95% of their life in the ADAF state (Hopkins+06, Cao 07)
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    Feng Yuan and Ramesh Naray 8 10 12 14 16

    18 20 log[ν(Hz)] 30 31 32 33 34 35 36 37 log[νL ν (erg s-1 )] Sgr A* Yuan+03, ApJ ADAF SED for the supermassive black hole at our Galactic Center, Sagittarius A*
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    Sample of beautiful nearby galaxies to test ideas about black

    holes astrophysics M81 NGC 1097 Sombrero
  53. 97.

    ur er- ar ral ty cal & ar he of

    he de id jet ly to ite Spiral galaxy NGC 1097, z = 0.01 4 R. S. Nemmen, T. Storchi-Bergmann and M. Eracleous Figure 1. Cartoon illustrating the model for the central engines of LLAGNs. It consists of three components: an inner ADAF, an outer truncated thin disc and a relativistic jet. of the model are illustrated in Fig. 1. We describe here the main features of this model. 3.1 ADAF component The inner part of the accretion flow is in the form of an ADAF which is a hot, geometrically thick, optically thin two-temperature accretion flow, which has low radiative efficiency (e.g. Kato, Fukue & Mineshige 1998; Narayan et al. 1998). ADAFs are characterized by the presence of outflows or winds, which prevent a considerable fraction of the gas that is available at large radii from being accreted on to the black hole. This has been suggested by numerical simula- tions (Hawley & Krolik 2001; Stone & Pringle 2001; De Villiers, Hawley & Krolik 2003; Igumenshchev, Narayan & Abramowicz 2003; Proga & Begelman 2003; McKinney & Gammie 2004; Yuan et al. 2012) and analytical work (Narayan & Yi 1994; Blandford & Begelman 1999; Narayan, Igumenshchev & Abramowicz 2000; Begelman 2012) (cf. Narayan et al. 2012 for an alternative view). In order to take this mass-loss into account, we follow Blandford & Begelman (1999) and introduce the parameter s by ˙ M = ˙ Mo R Ro s , (1) to describe the radial variation of the accretion rate ˙ Mo measured at the outer radius of the ADAF, Ro . The results of the numerical simu- lations of the dynamics of ADAFs previously mentioned as well as Chandra X-ray studies of NGC 3115 and Sgr A* (e.g. Wong et al. 2011; Wang et al. 2013) together with submillimetre polarization and Faraday rotation measurements of Sgr A* (Marrone et al. 2007) suggest that 0.3 s 1 (the lower bound is estimated from fitting the SED of Sgr A*; cf. Yuan, Quataert & Narayan 2003; Yuan, Shen & Huang 2006). Following these results, in our models we conservatively adopt s = 0.3 unless otherwise noted. been argued that the value of δ can be potentially increased due to different physical processes – such as magnetic reconnection – that affect the heating of protons and electrons in hot plasmas (e.g. Quataert & Gruzinov 1999; Sharma et al. 2007). Given the theoretical uncertainty related to the value of δ, we allow it to vary over the range 0.01 ≤ δ ≤ 0.5. The cooling mechanisms incorporated in the calculations are synchrotron emission, bremsstrahlung and inverse Comptonization of the seed photons produced by the first two radiative processes. Given the values of the parameters of the ADAF, in order to com- pute its spectrum we first numerically solve for the global structure and dynamics of the flow, as outlined in Yuan et al. (2000, 2003). Obtaining the global solution of the differential equations for the structure of the accretion flow is a two-point boundary value prob- lem. This problem is solved numerically using the shooting method, by varying the eigenvalue j (the specific angular momentum of the flow at the horizon) until the sonic point condition at the sonic radius Rs is satisfied, in addition to the outer boundary conditions (Yuan et al. 2003). There are three outer boundary conditions that the ADAF solution must satisfy, specified in terms of the three variables of the problem: the ion temperature Ti , the electron temperature Te and the radial velocity v (or equivalently the angular velocity ). Following Yuan, Ma & Narayan (2008), when the outer boundary of the ADAF is at the radius Ro = 104RS (where RS is the Schwarzschild radius), we adopt the outer boundary conditions Tout, i = 0.2Tvir , Tout, e = 0.19Tvir and λout = 0.2, where the virial temperature is given by Tvir = 3.6 × 1012(RS/R) K, λ ≡ v/cs is the Mach number and cs is the adiabatic sound speed. When the outer boundary is at Ro ∼ 102RS , we adopt the boundary conditions Tout, i = 0.6Tvir , Tout, e = 0.08Tvir and λout = 0.5. After the global solution is calculated, the spectrum of the accretion flow is obtained (see e.g. Yuan et al. 2003 for more details). We verified that if these boundary conditions are varied by a factor of a few, the resulting spectrum does not change much. 3.2 Thin disc component Our model posits that outside the ADAF there is an outer thin ac- cretion disc with an inner radius truncated at Rtr = Ro and extending up to 105RS such that the outer radius of the ADAF corresponds to the transition radius to the thin disc. The other parameters that describe the thin disc solution are the inclination angle i, the black hole mass and the accretion rate ˙ Mo (the same as the accretion rate at the outer boundary of the ADAF). The thin disc emits locally as a blackbody, and we take into account the reprocessing of the X-ray radiation from the ADAF. This reprocessing effect has only a little impact on the spectrum of the thin disc though, with the resulting SED being almost identical to that of a standard thin disc (e.g. Frank, King & Raine 2002). For sources without optical/UV constraints, we adopt Ro ∼ 104RS ; in this case we simply ignore the contribution of the thin disc emission since for Rtr ∼ 104RS the thin disc contributes very little to the emission compared to the ADAF. In sources for which we have available optical/UV data to constrain this component of the flow, we then explore models with Rtr < 104RS . at NASA Goddard Space Flight Ctr on February 6, 2014 Downloaded from Nemmen et al. 2014, MNRAS
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    Synchrotron + bremsstrahlung Inverse Compton scattering Blackbody Radiative efficiency ≪

    10% ADAFs explain low-luminosity AGNs (i.e. most galactic nuclei at z ~ 0) and stellar-mass black holes in low/hard state L/LEdd . 0.01 H/R ⇠ 1 ⌧ ⌧ 1 Ti ~ 1012 (RS /R) K Te ~ 109 - 1011 K radiate in all frequencies good at producing outflows/jets
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    Thermal state (NLS1s?) Intermediate state? (Quasars, Seyferts?) Hard state (LLAGNs,

    Seyferts) Quiescent state (LLAGNs, Sgr A*) M · a Quiescent state (Sgr A*) h/r ⇠ 1 ⌧ ⌧ 1 h/r ⌧ 1 ⌧ 1 ˙ M & 0.01 ˙ MEdd Adapted from Yuan & Narayan 2014, ARA&A Thermal state (Quasars, NLS1s?) ? ? A Unified View of Accretion Flows