truncated disc and x-ray spectral states of black holes
DESCRIPTION
Marek Gierli ński University of Durham. Truncated disc and X-ray spectral states of black holes. DISC. WARS. DISC. WARS. T RUNCATED DISC. THE. STRIKES BACK. Outline. X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model - PowerPoint PPT PresentationTRANSCRIPT
Truncated discand
X-ray spectral statesof black holes
Marek GierlińskiUniversity of Durham
TRUNCATED DISCSTRIKES BACK
THEDISCDISC
WARSWARS
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 4
Black hole binaries: transients
Done, Gierliński & Kubota 2007
1 year ASM (1.3-12 keV)
GX 339-4, 2002 outburst
Truncated disc and X-ray spectral states 26 March 2008 6
X-ray spectral states
• Spectral appearance changes as a function of luminosity
• Low luminosity (<0.01 LEdd): low/hard state
• High luminosity (>0.1 LEdd): high/soft and very high states
• Ultrasoft – extreme high/soft• I will generally distinguish
between hard and soft states
GRO J1655–40
Done, Gierliński & Kubota 2007
Truncated disc and X-ray spectral states 26 March 2008 7
Emission mechanisms
• Standard accretion disc: blackbody-like spectrum of temperature less then ~1 keV• Spectrum at higher energies: fraction of accretion power is dissipated in a hot,
optically thin medium• Emission mechanism: inverse Compton scattering of disc photons off hot electrons
Spectral states of Cyg X-1disc
ComptonisationSoft stateHard state
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 9
Optically thin plasma – Comptonisation
• Emission mechanism: repeated inverse Compton scattering of soft disc photons off hot electrons (Comptonisation)
• Comptonisation on Maxwellian electrons can explain the hard state
• Typical electron temperature ~ 100 keV
• Soft state requires non-thermal electrons
Hard statethermal
Soft statenon-thermal
Cyg X-1
Truncated disc and X-ray spectral states 26 March 2008 10
Seed photon input shapes the spectrum
Cooling (disc photons)
Heating(accretion)
Comptonisation
Less seed photons: harder
More seed photons: softer
Truncated disc and X-ray spectral states 26 March 2008 11
Varying hard-to-soft ratio, Lh/Ls
Varying ratio betwen seed photon input (Ls) and heating of electrons (Lh) changes the shape of the Comptonised spectrum. This can explain observed X-ray spectral states!
Theoretical model Data from Cyg X-1
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 13
What geometry?
• We need hot, optically thin plasma; but where?• The disc extends down to the last stable orbit and there is a
hot corona above the disc (Beloborodov 1999)
• The outer disc can be truncated at some radius and replaced be a hot inner flow (Esin, McClintock & Narayan 1997)
• Transition from a standard disc to the hot flow can be achieved by evaporation (Różańska & Czerny 2000)
The outer disc can be truncated at some radius and replaced be a hot inner flow (Esin, McClintock & Narayan 1997)
Truncated disc and X-ray spectral states 26 March 2008 14
Geometry of the truncated disc
black holeaccretion
dischot inner
flow
activeregion
jet
outflow
Truncated disc and X-ray spectral states 26 March 2008 15
Spectral states – moving truncation radius
Lh/Ls
hard state
hard state
soft state
soft state
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 17
Light curves – different timescales
• Available instruments allow us to observe X-ray sources with sub-millisecond resolution
• Black holes show variability on all timescales down to milliseconds
• A useful tool to study variability is Fourier transforms
• Create power spectra
Truncated disc and X-ray spectral states 26 March 2008 18
Power spectra
Quasi-periodic oscillations (QPOs) – unlike, e.g., pulsations, they are not coherent
Truncated disc and X-ray spectral states 26 March 2008 19
Do we understand power spectra?
• Not really• We have some idea how to
obtain certain frequencies (e.g. QPOs)
• These might come from disc oscillations, depend on size
• Moving the truncation radius will change frequency
Soft state – disc extending downhigher frequencies
Hard state – disc is truncatedlower frequencies
Truncated disc and X-ray spectral states 26 March 2008 20
Music of the truncated disc
• We can link the observed QPO frequency with the truncation radius in the disc
• There are frequencies in the disc: orbital, periastron and nodal precession
• Change in the truncation radius = change in the QPO frequency
Di Matteo & Psaltis (1999)
Hard
Soft
Truncated disc and X-ray spectral states 26 March 2008 21
Propagation of fluctuations – broad band PDS
RtruncRLSO
Frequency
P
Truncated disc and X-ray spectral states 26 March 2008 22
Propagation of fluctuations – broad band PDS
RtruncRLSO
Frequency
P
Truncated disc and X-ray spectral states 26 March 2008 23
Propagation of fluctuations – broad band PDS
RtruncRLSO
Frequency
P
Truncated disc and X-ray spectral states 26 March 2008 24
Behold the last stable orbit
• Hard-to-soft transition: decrease truncation radius, increase frequencies• The disc: high-pass filter• Last stable orbit: low-pass filter
Rtr RLSO
XTE J1550–564 Done, Gierliński & Kubota 2007
Truncated disc and X-ray spectral states 26 March 2008 25
Hard-to-soft transition
XTE J1650–500
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 27
Accretion disc at low luminosities (< 0.03 LEdd)
• Accretion rate • Truncation radius • Seed photon input
• Lh /Ls
• Spectrum softens
Lum
inosity
Ibragimov et al. 2005
Truncated disc and X-ray spectral states 26 March 2008 28
Accretion disc at low luminosities (< 0.03 LEdd)
• Accretion rate • Truncation radius • Disc irradiation • Reflection from the disc
Lum
inosity
Ibragimov et al. 2005 Spectral index
hard
soft
Ref
lect
ion
ampl
itud
e
Truncated disc and X-ray spectral states 26 March 2008 29
Accretion disc at low luminosities (< 0.03 LEdd)
• Accretion rate • Truncation radius • Timescales • QPO frequency
Lum
inosity
Axelsson et al. 2005
hard
soft
QPO frequency
Spe
ctra
l har
dnes
s
Truncated disc and X-ray spectral states 26 March 2008 30
Accretion disc at low luminosities (< 0.03 LEdd)
• Accretion rate • Truncation radius • High-pass filter • Power spectrum narrows
Lum
inosity
Gierliński, Done & Kubota 2007
hard
soft
Truncated disc and X-ray spectral states 26 March 2008 31
Jet in the hard state
• Jets are strongly suppressed in the soft state• Meier (2005): vertical magnetic field in the hot inner flow is required to
launch a jet (magnetically-dominated accretion flow)• Needs truncated disc!
Meier & Nakamura 2006
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 33
Prominent disc in the hard state?...
• Miller et al. (2006) analysed XMM-Newton and RXTE data of GX 339–4
• Hard-state X-ray spectra• They found very small inner
radius of the disc, comparable to the last stable orbit
• Does this rule out the truncated disc model?
Prominentdisc
after Miller et al. 2006
GX 339-4
Truncated disc and X-ray spectral states 26 March 2008 34
Prominent disc in the hard state?... maybe
• Miller et al. (2006) analysed XMM-Newton and RXTE data of GX 339–4
• Hard-state X-ray spectra• They found very small inner
radius of the disc, comparable to the last stable orbit
• Does this rule out the truncated disc model?
• X-ray spectral fitting is complicated and non-unique
• Some hard-state spectra show a soft excess above the disc (Ebisawa et al. 1996; Wilms et al. 1999; Di Salvo et al. 2001; Ibragimov et a. 2005)
Prominentdisc
after Miller et al. 2006
GX 339-4
Truncated disc and X-ray spectral states 26 March 2008 35
Soft excess above the disc
Brokenpower law
Wilms et al. 1999 (ASCA)Broken power law to account for the soft excess
GX 339-4
Disc
Soft excess
Soft excess
Cyg X-1 Cyg X-1
Di Salvo et al. 2001 (SAX)Additional thermal Comptonisation hotter than the disc
Ibragimov et al. (2005) (RXTE)Non-thermal Comptonisation; disc so cool and outside RXTE band
The soft excess, when added to the model, pushes the disc away: decreasing its temperature and increasing its inner radius
Truncated disc and X-ray spectral states 26 March 2008 36
More problems with the truncated disc model
• Rykoff et al. (2007) analysed Swift observations of a transient XTE J1817-330
• They traced the transition from the soft to the hard state
• Picture shows luminosity-temperature diagram
• The disc seems to keep constant inner radius during transition
• This is a killer for the truncated disc model!
• Or is it?
Rykoff et al. 2007
Truncated disc and X-ray spectral states 26 March 2008 37
Accretion disc in the hard state
• RXTE (green) and Swift (black) data during the outburst
• Results from multicolour blackbody disc model
• Soft state: inner radius remarkably constant
• Transition: disc recedes!• Hard state: disc comes back?
soft hard
Gierliński, Done & Page 2008
Dis
c ra
dius
(a
rbit
rary
uni
ts)
Outline
X-ray spectral statesHard state and Comptonisation
Geometry of the accretion flow
Variability
Truncated disc modelPotential problem: strong disc in the hard state
Solution: irradiated disc model
Conclusions
Truncated disc and X-ray spectral states 26 March 2008 39
Irradiated disc
• Hot plasma produces hard X-ray spectrum
• Regardless of the geometry the hot flow illuminates the disc
• We see this: hard X-rays are reflected, typically /2 ~ 0.3
• If there is reflection there must be reprocessing:
Lrep = /2 (1 – a) LComp
• Effectively, an inner portion of the disc is heated up by irradiation
Gierliński, Done & Page 2008
LCompLrep
Truncated disc and X-ray spectral states 26 March 2008 40
Irradiated disc
• Hot plasma produces hard X-ray spectrum
• Regardless of the geometry the hot flow illuminates the disc
• We see this: hard X-rays are reflected, typically /2 ~ 0.3
• If there is reflection there must be reprocessing:
Lrep = /2 (1 – a) LComp
• Effectively, an inner portion of the disc is heated up by irradiation
• Explanation for the soft excess!• If fitted by a standard disc
model, temperature is overestimated and the inner radius underestimated
Gierliński, Done & Page 2008
0.1
Intrinsic discemission Effect of
irradiation
LCompLrep
Truncated disc and X-ray spectral states 26 March 2008 41
Effect of irradiation on disc radius
• The graph shows RXTE (green) and Swift observations interpreted with standard and irradiated disc models
• There is no difference in the soft state (no irradiation)
• During the transition and in the hard state the inner disc radius is larger when irradiation is taken into account
• More effects that can lead to underestimated disc radius:
– No stress-free boundary condition, appropriate for LSO (2.7)
– Varying colour correction (1.5)– Scattering in the corona (2–3)
• After corrections the disc recedes continuously with decreasing flux
Gierliński, Done & Page 2008
soft
Dis
c ra
dius
hard
standard disc
irradiated disc
irradiated disc with nostress-free boundarycondition
softhard
standard disc
irradiated disc
irradiated disc with nostress-free boundarycondition
XTE J1817-330
Truncated disc and X-ray spectral states 26 March 2008 42
Irradiated outer disc
• Let us assume that a (small) fraction of the central X-ray flux illuminated the outer disc
• Could be scattered back to the disc by outflowing material
• Could be warped disc• This changes the shape of the
standard disc blackbody
Gierliński, Done & Page 2008
Truncated disc and X-ray spectral states 26 March 2008 43
Fit the UV data (Swift UVOT+XRT)XTE J1817-330 Gierliński, Done & Page
2008
Truncated disc and X-ray spectral states 26 March 2008 44
Hard state is different
• Irradiation fraction fout: what fraction of central X-ray luminosity is intercepted by the outer disc
• Plot versus spectral state
• Soft state: fout ~ 10-3
• Hard state: fout ~ 710-3
• Increased vertical size of corona?
• Contribution from jet?
Comptonisation-to-disc ratio
Irra
dia
tion
fr
act
ion
soft
transition
hard
Gierliński, Done & Page 2008
Truncated disc and X-ray spectral states 26 March 2008 45
Conclusions
• X-ray binaries make an excellent laboratory for accretion physics
• We can easily study various spectral states at various luminosities
• Truncated disc model: in the hard state the inner disc is replaced by hot optically thin flow
• Hugely supported by spectral and timing data; as disc recedes:– Spectrum hardens– Reflection amplitude drops– QPO frequencies decrease– Power spectrum broadens
• Some recent observations interpreted with simple models contradicted truncated disc
• The truncated disc strikes back: irradiated disc model is consistent with new data
TRUNCATED DISCSTRIKES BACK
THEDISCDISC
WARSWARS
DURHAM UNIVERSITY PRODUCTION
WRITTEN BYMAREK GIERLIŃSKI
ANDCHRIS DONE
PERFOMED BYMAREK GIERLIŃSKI
PICTURES BYMAREK GIERLIŃSKI
MUSICTHE DEAFS
X-RAY SATELLITESPROVIDED BYNASA & ESA
COMMISSIONED BYJURI POUTANEN
SPONSORED BYTHE MINISTRY OF EDUCATION
OF POLAND
All sources depicted in this presentation are not fictional.Any resemblance to actual black holes,
accretion discs and X-ray binaries,living or dead, is purely intentional.
DISCLAIMER: this talk is presented ‘as-is’ and without warranty of any kind. In no event shall the authors be liable for any special, incidental, indirect or consequential damages, whatsoever,
including, without limitation, heart attack, cerebral haemorrhage, stupor, cataract, epilepsy, remorse, gastric ulcer, Nobel prize, appendicitis, gout, death or resurrection, whether or not
advised of the possibility of damage, and on any theory of liability, arising out of or in connection with the use or inability to use this talk.
Truncated disc and X-ray spectral states 26 March 2008 47
Broad line in GX 339-4?
• Diskbb + power law + Laor line fit gives line with Rin= 40.4 Rg
(Miller et al 2006)
• Inconsistent with truncated disc• But Comptonisation gives
continuum with high and low energy cutoff – but now depends how model reflection Rin=10 3Rg with good models or 4 0.4 Rg with pexriv!
• Irradiated truncated disc can have yet more complex continuum! Crucially determines the extent of the red wing of the line…..
Done, Gierliński, Díaz Trigo 2008