accretion flows onto black holes
DESCRIPTION
Accretion flows onto black holes. Chris Done University of Durham. Observed disc spectra. Bewildering variety Pick ONLY ones that look like a disc! L/L Edd T 4 max (Ebisawa et al 1993; Kubota et al 1999; 2001) Constant size scale – last stable orbit!! - PowerPoint PPT PresentationTRANSCRIPT
Accretion flows onto black holes
Chris DoneUniversity of Durham
Observed disc spectra
• Bewildering variety• Pick ONLY ones that look like a
disc! • L/LEdd T4
max (Ebisawa et al 1993; Kubota et al 1999; 2001)
• Constant size scale – last stable orbit!!
• Proportionality constant gives a measure Rlso i.e. spin
• Consistent with low to moderate spin not extreme spin nor extreme versions of higher dimensional gravity - braneworlds (Gregory, Whisker, Beckwith & Done 2004)
Gierlinski & Done 2003
Disc spectra: last stable orbit
• Bewildering variety• Pick ONLY ones that look like a
disc! • L/LEdd T4
max (Ebisawa et al 1993; Kubota et al 1999; 2001)
• Constant size scale – last stable orbit!!
• Proportionality constant gives a measure Rlso i.e. spin
• Consistent with low to moderate spin not extreme spin nor extreme versions of higher dimensional gravity - braneworlds (Gregory, Whisker, Beckwith & Done 2004)
• Bewildering variety of spectra from single object
• Underlying pattern
• High L/LEdd: soft spectrum, peaks at kTmax often disc-like, plus tail
• Lower L/LEdd: hard spectrum, peaks at high energies, not like a disc
Gierlinski & Done 2003
But rest are not simple…
• Collision – redistribute energy• If photon has more energy than
electron then it loses energy – downscattering
• If photon has less energy than electron then it gains energy – upscattering
• Easiest to talk about if scale energies to mc2
• Electron energy mc2 just denoted or =kT/mc2
• Photon energy becomes =h/mc2=E/511 for E (keV)
Compton scattering theory
inout
~ 4 – max
)
How much scattering ? • Compton scattering seed
photons from accretion disk. Photon energy boosted by factor ~ 4if thermal in each scattering.
• Number of times scattered given by optical depth,nR
• Scattering probability exp(-) • Optically thin << 1 prob ~ average number ~
• Optically thick >>1 prob~1 and average number ~ • Total fractional energy gain =
frac.gain in 1 scatt x no.scattCompton y ~
R
Optically thin thermal compton
Log Log
Log
N(
Log
f
• power law by multiple scattering of thermal electrons f () • index =log(prob)/log(energy boost) ~ -log /log (1+4)
• More generally depends on , or y) steeper if small , and/or • BUT BUMPY spectrum if <<1
Optically thin thermal compton
Log Log
Log
N(
Log
f
• power law by multiple scattering of thermal electrons f () • index =log(prob)/log(energy boost) ~ -log /log (1+4)
• More generally depends on , or y) steeper if small , and/or • BUT BUMPY spectrum if <<1
Cyg X-1: Gierlinski et al 1999
• kTe~ 100keV so • Spectral index~0.6 so ~1 smooth spectrum as seen!
Cyg X-1: Gierlinski et al 1999
• kTe> 500keV so • Spectral index~1.2 so =0.02 so should be bumpy! But
its smooth!!!
Optically thin nonthermal compton• power law by single scattering of nonthermal electrons N () p
• index = (p-1)/2
• Starts a factor down from seed photons, extends to max2 in
• Ends at max
Log Log
Log
N(
Log
f
N () p
f() p-1)/2
max in max2 in
Cyg X-1: Gierlinski et al 1999
• Nonthermal - single scattering
• kTbb=0.2 keV boosted by 2 to max = max2 kTbb> 1000 keV
so max > 70!!!
• Spectral index a=1.2=(p-1)/2 so N()=3.4 not dependent on for nonthermal! So harder to constrain
• Outburst starts hard, source stays hard as source brightens• Then softens to intermediate/very high state/steep power law state
major hard-soft state transition• Then disc dominated, then hardens to make transition back to
low/hard state – hysteresis as generally at lower L
Hardness – intensity diagramF
ender Belloni &
Gallo 2004
• No special QSO class – they ALL produce jets, consistent with same radio/X ray evolution
• Jet links to spectral state • Steady jet in low/hard state, power
depends on accretion rate! i.e. L/LEdd (Merloni et al 2003; Falke et al 2004)
so jet powered by mass accretion rate ie gravity
• Bright radio flares in rapid low/hard to high/soft associated with outbursts. (Fender et al 2004)
Gallo et al 2003
And the radio jet… link to spin?
• Disc models assumed thermal plasma – not true at low L/LEdd
• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)
• Hot electrons Compton upscatter photons from outer cool disc
• Few seed photons, so spectrum is hard
• Jet from large scale height flow velocity linked to launch radius
Accretion flows without discs
Log
Log
f
(
Moving disc – moving QPO• Low frequency QPO – very strong feature at softest low/hard and
intermediate and very high states (disc+tail)
• Moves in frequency: correlated with spectrum• Moving inner disc makes sense of this. Disc closer in, higher f QPO.
More soft photons from disc so softer spectra (di Matteo et al 1999)
DGK07
• Disc models assumed thermal plasma – not true at low L/LEdd
• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)
• Hot electrons Compton upscatter photons from outer cool disc
• Few seed photons, so spectrum is hard
• Jet from large scale height flow velocity linked to launch radius
Accretion flows without discs
Log
Log
f
(
• Disc models assumed thermal plasma – not true at low L/LEdd
• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)
• Hot electrons Compton upscatter photons from outer cool disc
• Few seed photons, so spectrum is hard
• Jet from large scale height flow velocity linked to launch radius
Log
Log
f
(
No inner disc
• Disc models assumed thermal plasma – not true at low L/LEdd
• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)
• Hot electrons Compton upscatter photons from outer cool disc
• Few seed photons, so spectrum is hard
• Jet from large scale height flow velocity linked to launch radius
Log
Log
f
(
No inner disc
• Disc models assumed thermal plasma – not true at low L/LEdd
• Instead: hot, optically thin, geometrically thick inner flow replacing the inner disc (Shapiro et al. 1976; Narayan & Yi 1995)
• Hot electrons Compton upscatter photons from outer cool disc
• Few seed photons, so spectrum is hard
• Jet from large scale height flow velocity linked to launch radius collapse of flow=collapse of jet
Log
Log
f
(
Collapse of hot inner flow
Decrease fraction of power in nonthermal reconnection above disc
Decrease inner disc radius, and maybe radial extent of corona giving increasing LF QPO frequency
VHS
LS (bright)
LS (dim)
VHS
HS
HS
Disc to minimum stable orbit
Done Gierlinski & Kubota 2007
Jet gets faster, catches up with slower outflow, get flares of radio emission from internal shocks Fender (2004)
No jet
• Appearance of BH should depend only on mass and spin (black holes have no hair!)
• Plus mass accretion rate, giving observed luminosity L
• Maximum luminosity ~LEdd where radiation pressure blows further infalling material away
• Get rid of most mass dependance as accretion flow should scale with L/LEdd
• 104-1010 M: Quasars • 10-1000(?) M: ULX • 3-20 M: Galactic black holes
Black holes
• Stretched out by lower disc temperature so not so obvious as in BHB but still….
• …AGN NOT all the same underneath absorption!! Their SED should depend intrinsically on L/LEdd in same way as BHB
• So need to know AGN mass in order to calculate LEdd
AGN spectral states
Mass of AGN??• Magorrian-Gebhardt relation gives BH mass!! Big black holes live
in host galaxies with big bulges! Either measured by bulge luminosity or bulge mass (stellar velocity dispersion) or BLR
Bla
ck h
ole
mas
s
Stellar system mass
103
109
1061012
AGN/QSO Zoo!!! Optical • Bright, blue continuum
from accretion disc. Gas close to nucleus irradiated and photo-ionised – lines!
• Broad permitted lines ~ 5000 km/s (BLR)
• Narrow forbidden lines ~ 200 km/s (NLR)
• Forbidden lines suppressed if collisions so NLR is less dense than BLR
• Lines give diagnositic of unobservable EUV disc continuum
Francis et al 1991
AGN/QSO Zoo!!! Optical
• Bigger range in mass 105-109
• L varies without much else changing if same L/LEdd with different BH mass: Sey/QSO
• Cold absorption from torus along equatorial plane
• BLR and disc within torus so obscured if line of sight intersects torus. See only NLR
• But can see BLR in polarised (scattered!) light
• Unification of narrow and broad line Sey1/Sey 2 via inclination
AGN/QSO unification
Urry & Padovani 1995
AGN/QSO Zoo!!! Radio loud• Some have enormous, powerful jets on Mpc scales• How QSO first found. But now most known to be radio quiet• FRI (fuzzy lobes, 2 sided jet) FRII (bright hot spot, 1sided jet)
VHS
NLS1
HS
QSO
US
QSO
Hard (low L/LEdd)
Soft (high L/LEdd)
Done & Gierliński 2005
LS
LINERS?
AGN • Origin of jet – L/LEdd ?
• But standard QSO’s can be radio loud OR radio quiet at high L/LEdd
• Environment difference? Radio loud in ellipticals so can have high spin from accretion spinup in major mergers
• Low spin in spirals from random orientation small accretion events (Sikora Stawarz & Lasota 2007)
AGN/QSO Zoo!!! Host galaxy• Link to galaxy formation – ellipticals/bulge from major mergers so
accretion spins up BH to maximal – more powerful jet• Spirals from
random small satellite galaxy accretion – low spin (Volonteri et al 2007)
Conclusions• Test GR - X-rays from accreting black holes produced in regions
of strong gravity
• Last stable orbit (ONLY simple disc spectra) L T4max
• Low to moderate spin in LMXB as expected
• Corrections to GR from proper gravity must be smallish
• Accretion flow NOT always simple disc – X-ray tail!
• Mass ~10 Msun. Accretion flow + jet change with L/LEdd
• Apply to AGN – mass has bigger spread (105-9 Msun)
• More complex environment – torus/dust obscuration – inclination!
• Spectrum and jet change with L/LEdd but jet probably depends on spin as well. Feedback from this controls galaxy formation
• PHYSICS ASTROPHYSICS ASTRONOMY
Relativistic smearing: spin
Fabian et al. 1989
Energy (keV)
flux
• Relativistic effects (special and general) affect all emission
• Emission from side of disc coming towards us: – Doppler blueshifted– Beamed from length contraction– Time dilation as fast moving
(SR)– Gravitational redshift (GR)
• Fe Kline from irradiated disc should be broad and skewed, and shape depends on Rin (and spin)
Observations: tail as well as disctail probably Compton scattering
Cyg X-1: Gierlinski et al 1999
• High state spectra need predominantly non-thermal electron distribution
• Low state spectra peak at 100 keV. Well modelled by thermal electron distribution
Optically thick thermal
Log Log
Log
N(
Log
f
• Optical depth multiple scattering – average N ~ 2
• Not much left of original seed photon spectrum exp(-)• if (1+4) N in > 3 (y>>1) then majority of photons reach 3
• Can’t go any higher so they pile up – try to thermalise but little true absorption so still comptonised. Wien peak.
Practice!! Thermal compton
• Suppose kTe=100 keV and • Calculate k• Spectrum extends to ~3keV• Calculate y=( • Is y>> 1 ie does spectrum thermalise? if not, calculate the
spectral index = -log /log (1+4+162)
• Original blackbody seed at kTbb=0.2 keV• Only e of original blackbody seen • Sketch spectrum in vfv – we have f () so plot as f ()
Practice!! Mystery object
• But do see more disc than expected! Says some disc photons don’t intercept the hot flow ie diagnostic of geometry!!
Synchrotron (self compton)• Same as compton scattering except seed photons are virtual from
magnetic field cyc = eB/2 mc = 2.8x106 B Hz so radio
• Normally deal with nonthermal so energy boost is 2
Log Log
Log
N(
Log
f
N () p
f() p-1)/2
max cyc max2 in
Bremstrahlung: hot gas • Classical way is electron accelerates in field of atom so radiates
Log
Log
f
f() n2 T1/2 e-
cyc max2 in
Bremstrahlung• But easier way to think is that it’s the same as compton scattering
except seed photons are virtual from electric field• Self compton if ni ne < ne n (density of photon field) so compton
dominates in radiation dominated environments (black hole accretion flows) and brems dominates in rarified hot gas (galaxies + clusters)
Log Log
Log
N(
Log
f
f() n2 T1/2 e-
cyc max2 in
Bremstrahlung• But easier way to think is that it’s the same as compton scattering
except seed photons are virtual from electric field
• Temperatures of 104-107 K dominated by LINES
Log
Log
f
f() n2 T1/2 e-
cyc max2 in
Bremstrahlung• Same as compton scattering except seed photons are virtual from
electric field
• Temperatures of 104-107 K dominated by LINES
• Below 103 K then electrons bound in H atoms so no brems anyway!
Log Log
Log
N(
Log
f
f() n2 T1/2 e-
cyc
Log
Conclusions• Compton scattering – just photon and electrons!• Incredible variety and subtle interplay• Only approximately a power law• low energy break (seed photons)• high energy break (mean electron energy)• Thermal – black hole tail in low/hard state• Nonthermal – black hole tail in high states• Synchrotron - compton scattering of virtual B photons • Then can self-comptonise (Sync-self-compton) –jets!• Hot gas – clusters and galaxy halo where electrons scatter
virtual photons from electroic field of ion.
Transients• Huge amounts of data, long term variability (days –years) in mass
accretion rate (due to H ionisation instability in disc)• Observational template of accretion flow as a function of L/LEdd
onto ~10 M BH
DGK072 years
• Differential Keplerian rotation
• Viscosity B: gravity heat
• Thermal emission: L = AT4
• Temperature increases inwards until minimum radius Rlso(a*) For a*=0 and L~LEdd Tmax is
• 1 keV (107 K) for 10 M
• 10 eV (105 K) for 108 M
• big black holes luminosity scales with mass but area scales with mass2 so T goes down with mass!
• Maximum spin Tmax is 3x higher
Spectra of accretion flow: disc
Log
Log
f
(