galactic black hole binaries

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GBH AGN Galactic Black Hole Binaries Miniature versions of AGNs Emily Alicea-Muñoz Astro 597A 18 October 2004

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GBH. Galactic Black Hole Binaries. Miniature versions of AGNs. AGN. Emily Alicea-Mu ñoz Astro 597A 18 October 2004. Outline. Overview SXTs, LMXBs, HMXBs The case for BHBs and BHCs and not for NSBs Accretion Mechanisms - PowerPoint PPT Presentation

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Page 1: Galactic Black Hole Binaries

GBH

AGN

Galactic Black Hole BinariesMiniature versions of AGNs

Emily Alicea-MuñozAstro 597A18 October 2004

Page 2: Galactic Black Hole Binaries

Outline• Overview

– SXTs, LMXBs, HMXBs– The case for BHBs and BHCs and not for NSBs– Accretion Mechanisms

• BHXRB states and their oh-so-confusing classification schemes (ugh, so many acronyms)

– Luminosity classification scheme– McClintock-Remillard classification scheme

• Cyg X-1: NGC 4051’s Mini-me?

• Microquasars – AGN/QSO’s Mini-me’s; are they related to GRBs too?

Page 3: Galactic Black Hole Binaries

Overview

Page 4: Galactic Black Hole Binaries

Overview: SXTs• Soft X-ray Transients (SXT)

– short period binaries (5hrs – 6 days)– late-type (K-M) type secondaries– rare, dramatic x-ray outbursts (L > 1038 erg s-1)

• LMXB: low-mass x-ray binaries– most of them strong black hole candidates (BHC)– optical spectra are hot, blue continua (U-B ~ -1) with superposed

broad H and He emission lines arising from the inner disk region

• HMXB: high-mass x-ray binaries– early-type (O-B) secondaries– most have NS instead of BH (with a few exceptions, e.g. Cyg X-1)

Page 5: Galactic Black Hole Binaries

SXT Observations• Outbursts

– once every ~10-20 yrs– fast rise followed by exponential decay– mini-outbursts sometimes in their way to quiescence– ultra-soft x-ray spectra during outburst, with blackbody

color temperature of kT ~ 0.5-1 keV superposed on hard power-law extending to higher energies

• Quiescence– mass transfer continues at a very low rate– inner accretion disk turns into hot, low density corona– radiatively inefficient advective accretion– SXTs with BH fainter than those with NS because of

event horizon (energy is lost)

Page 6: Galactic Black Hole Binaries

SXT Observations• X-ray Spectroscopy and Variability

– presence of type-I x-ray bursts indicates primary is NS– rapid quasi-periodic oscillations (QPOs) allow study of

inner accretion disk; often indicates presence of BH– two different x-ray states

• hard power-law spectrum extending to high energies– explained by Comptonization– predicts energy-dependent time delay

• soft blackbody spectrum– arising from inner region of accretion disk– Multicolor Disk Model (MCD) – temperature varies with radius

– situation not so simple as “two clearly defined” states; more details later...

Page 7: Galactic Black Hole Binaries

SXT Observations• Black Hole Spin

– affects innermost stable circular orbit (ISCO)– maximal spin makes ISCO smaller

• Radial Velocity Curves– measured during quiescence– can also determine secondary’s spectral type and

orbital period– mass function can be calculated from K-velocity

amplitude

– inclination is most uncertain parameter

22

333

)(sin

2)(

MMiM

GPKMf

X

X

Page 8: Galactic Black Hole Binaries

BHB & BHC vs. NSB

Page 9: Galactic Black Hole Binaries

Accretion Mechanisms• Best Model: Thin Accretion Disk

– secondary fills its Roche equipotential lobe– narrow stream of gas escapes through first Lagrangian

point (L1)– gas with high angular momentum cannot directly

accrete onto BH, thus forming an accretion disk– gas in disk moves in Keplerian orbits with angular

velocity (GM/R3)1/2

– viscosity transports angular momentum outward– gas gets hotter closer to the BH– disk terminates at ISCO:

• RISCO = 6Rg = 6GM/c2, for a Schwarzschild BH

• RISCO = RG = GM/c2, for a Kerr BH

Page 10: Galactic Black Hole Binaries

Accretion Mechanisms• Another Model: MCD

– multi-temperature (multicolor) disk– used to describe thermal component in x-ray spectra– total disk luminosity in steady state

– limitation: neglect of torque-free boundary condition at ISCO

• MCD temperature profile T(R) R-3/4 (maximum at ISCO)• proper boundary condition sets maximum at R > RISCO

– relativistic MHD corrections – add a magnetic field and you extract energy from very near the horizon

indisk R

MGML2

Page 11: Galactic Black Hole Binaries

X-Ray States: Luminosity• Very High State (VHS)

– strong ultra-soft (US) component and unbroken power-law (PL) component; strong QPOs at ~ 10Hz

• High/Soft State (HS)– US dominates; very weak PL component; high luminosity; MCD

• Intermediate State – US and steeper PL at high energies

• Low/Hard State (LH)– no US component; hard power-law PDS (power density

spectrum); ~ 1.7 (2-20keV); low luminosity; radio emission

• Quiescent State– truncated disk; ADAF down to the ISCO

Page 12: Galactic Black Hole Binaries

X-Ray States: Luminosity“Unified MCD and ADAF model”

Page 13: Galactic Black Hole Binaries

X-Ray States• Limitations of luminosity classifications

– unified MCD and ADAF model don’t account well for the VHS’s unbroken power-law

– ordering states by accretion rate or luminosity is “naïve”

– model does not account for dynamical behavior of corona (flares, QPOs, radio emission)

– no quantitative model relating disk truncation to accretion rate

• McClintock & Remillard (2004) propose new scheme, based on a model consisting of a MCD and a power law component

Page 14: Galactic Black Hole Binaries

X-Ray States: McC & R• Quiescent State

– extraordinarily faint (Lx = 1030.5-1033.5 erg s-1)– distinctly non-thermal, hard spectrum (= 1.5 – 2.1)– long period systems brighter than short period systems– ADAF/MCD model accounts

for observed properties• hard PL spectra• faintness of BHBs relative to

NSBs• optical/UV time delay of X-ray

novae• broadband spectrum• truncated accretion disk

Page 15: Galactic Black Hole Binaries

X-Ray States: McC & R• Thermal-Dominant (TD)

– new name for the HS state– soft x-rays represent thermal

emission from inner disk, dominant below 10keV

– steep PL ( = 2.1 – 4.8)– PDS shows weak variability

and power scaling roughly as -1, indicative of turbulence

– “The set of conditions for which the disk-flux fraction is above 75% (2-20keV), the PDS shows no QPOs, and weak power continuum”

Page 16: Galactic Black Hole Binaries

X-Ray States: McC & R• Hard X-Ray State

– take out “low” from name (some sources show high luminosity)

– PL with ~ 1.7– broad enhancement at 20-

100keV (reflection of PL from surface of inner disk)

– steep cut-off near 100keV– compact quasi-steady radio

jets present (disappear upon return to TD state)

– physical conditions that give rise to this state are still debated

Page 17: Galactic Black Hole Binaries

X-Ray States: McC & R• Hard X-Ray State

– blackbody radiation truncated at large radius ~100Rg

– what’s going on inside this radius?• truncated disk, inner region filled by ADAF?• relativistic flow entrained in a jet?• disk intact but depleted of energy in some sort of Compton corona?

– answer could be found by • optical/x-ray variability studies• spectral analysis focused on broad Fe emission features

– origin of x-ray PL also debated – many possible mechanisms– “Association of hard state with radio jet is an important step

forward. […] HS is well characterized by three conditions: spectrum dominated (>80% at 2-20keV) by power law, spectral index in the range 1.5 < < 2.1, and a strong integrated power continuum”

Page 18: Galactic Black Hole Binaries

X-Ray States: McC & R• Steep Power-Law (SPL)

– new name for VHS– often exceedingly bright

(Lx>0.2LEdd), but not always– very steep unbroken (x-ray to

gamma-ray) PL ( ≥ 2.4)– QPOs in 0.1–30 Hz range– no evidence for high-energy

cutoff– transitions between TD and H

states usually pass through SPL state

– essentially radio-quiet; though sometimes shows impulsive jets

Page 19: Galactic Black Hole Binaries

X-Ray States: McC & R• Steep Power-Law (SPL)

– physical origin still an outstanding problem– spectrum extends to ~1MeV, maybe higher– possible model:

• inverse Compton scattering for a radiation mechanism• scattering occurs in a non-thermal corona• where do the Comptonizing electrons come from?

– magnetic instabilities in accretion disk?– strongly magnetized disk, as in AGNs?

• PL gets stronger and steeper as disk luminosity and radius decrease, while keeping high temperature

• Intermediate States– “State transitions and hybrid emission properties are to be

expected; x-ray spectra and PDS should be interpreted as intermediate states when necessary, while specifying which states can be combined to yield he observed x-ray properties”

Page 20: Galactic Black Hole Binaries

Cyg X-1• Unusual spectrum

– soft state dominated by PL instead of TD spectrum

– transition from hard to soft x-ray spectrum considered as one from the hard state to the SPL state

– weird SPL: no QPOs and low luminosity

– reminiscent of NGC 4051 (flashback to Week 5)

– hints that the same physical mechanism generating variability regardless of BH size

NGC 4051

Cyg X-1

Page 21: Galactic Black Hole Binaries

Microquasars• BHXRBs that eject

plasma at relativistic speeds (jets)

• Fossil sources of GRBs?

• Analogy with AGN/QSO– length and time scales

are proportional to BH mass

Page 22: Galactic Black Hole Binaries

Microquasars

Page 23: Galactic Black Hole Binaries

Microquasars• A connection between x-ray flux and jets has

been observed– jets appear when disk x-ray flux drops– jets are produced during replenishment of inner

accretion disk– time delay between jet flares at different wavelengths

consistent with adiabatically expanding cloud model– delay of few min between drop in x-ray flux and onset

of jets could indicate absence of material border, thus making the case for a BH event horizon

• however, absence of evidence is not evidence of absence, so this observation could have an alternative explanation

Page 24: Galactic Black Hole Binaries

Microquasars

Page 25: Galactic Black Hole Binaries

Microblazars• Microquasars with jet axis with <10° angle with

line of sight should be analogous to blazars• Should appear as intense sources of high-energy

photons with very fast variations in flux• Very hard to observe• It has been proposed that microblazars may be

more frequently linked to HMXBs– gamma-rays produced by inverse Compton of the jet

particles with the UV photons radiated by massive secondary

Page 26: Galactic Black Hole Binaries

Microquasars• X-ray/radio correlations

– hard x-ray state w/ radio jets also proposed for AGNs• Time variation correlations

– duration of x-ray flares from stellar-mass BHs and AGNs (e.g. Sgr A*) seem proportional to BH mass

– minimum frequencies of QPOs expected to be proportional to BH mass, for a given BH spin

• Iron K correlations– AGN: broad Fe K line, skewed to low energies– consistent with emission from surface of accretion disk– also observed for BHXRBs (post-Chandra era)

Page 27: Galactic Black Hole Binaries

Microquasars and GRBs?• Mirabel (2004) adopts the theory that long GRBs

might be caused by formation of BH in collapsars or highly magnetized neutron stars

• The case for the microquasar connection:– spin-orbit interactions provide enough power for

collapsar– GRBs seem associated with SN Ic, the ones that show

no H or He lines • progenitor lost outer layers way before event • could be due to progenitor being in a binary system which

underwent a common-envelope phase

Page 28: Galactic Black Hole Binaries

Microquasars/AGNs/GRBs

Page 29: Galactic Black Hole Binaries

GBH

Questions?(hopefully I’ll be able to answer them)

References:P.A. Charles: astro-ph/9806217 J.E. McClintock & R.A. Remillard: astro-ph/0306213I.F. Mirabel: astro-ph/0405433