truncated disc and x-ray spectral states of black holes marek gierliński university of durham

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


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


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



Variability



Conclusions


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


Seed photon input shapes the spectrum

Cooling (disc photons)

Heating(accretion)

Comptonisation

Less seed photons: harder

More seed photons: softer


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



Variability



Conclusions


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)


Geometry of the truncated disc

black holeaccretion

dischot inner

flow

activeregion

jet

outflow


Spectral states – moving truncation radius

Lh/Ls

hard state

hard state

soft state

soft state

Outline



Variability



Conclusions


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


Power spectra

Quasi-periodic oscillations (QPOs) – unlike, e.g., pulsations, they are not coherent


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


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


Propagation of fluctuations – broad band PDS

RtruncRLSO

Frequency

P



RtruncRLSO

Frequency

P


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


Hard-to-soft transition

XTE J1650–500

Outline



Variability



Conclusions


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



• 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



• Accretion rate • Truncation radius • Timescales • QPO frequency

Lum

inosity

Axelsson et al. 2005

hard

soft

QPO frequency

Spe

ctra

l har

dnes

s



• Accretion rate • Truncation radius • High-pass filter • Power spectrum narrows

Lum

inosity

Gierliński, Done & Kubota 2007

hard

soft


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



Variability



Conclusions


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


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


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


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


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



Variability



Conclusions


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


LCompLrep


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


0.1

Intrinsic discemission Effect of

irradiation

LCompLrep


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


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


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



Fit the UV data (Swift UVOT+XRT)XTE J1817-330 Gierliński, Done & Page

2008


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



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.


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

truncated disc and x-ray spectral states of black holes marek gierliński university of durham

Documents

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standard disc

outer disc

disc beloborodov

disc wars slide

observed xray spectral

hard state solution

t runcated disc strikes