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Truncated disc and X-ray spectral states of black holes

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

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Truncated disc and X-ray spectral states of black holes

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  1. Marek GierlińskiUniversity of Durham Truncated discandX-ray spectral statesof black holes

  2. DISC WARS DISC WARS TRUNCATED DISC THE STRIKES BACK

  3. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  4. Truncated disc and X-ray spectral states Black hole binaries: transients 1 year ASM (1.3-12 keV) Done, Gierliński & Kubota 2007

  5. GX 339-4, 2002 outburst

  6. Truncated disc and X-ray spectral states X-ray spectral states GRO J1655–40 • 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 Done, Gierliński & Kubota 2007

  7. disc Comptonisation Truncated disc and X-ray spectral states Emission mechanisms Spectral states of Cyg X-1 • 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 Soft state Hard state

  8. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  9. Truncated disc and X-ray spectral states Optically thin plasma – Comptonisation Cyg X-1 • 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

  10. Less seed photons: harder Heating(accretion) More seed photons: softer Cooling (disc photons) Truncated disc and X-ray spectral states Seed photon input shapes the spectrum Comptonisation

  11. Truncated disc and X-ray spectral states Varying hard-to-soft ratio, Lh/Ls Theoretical model Data from Cyg X-1 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!

  12. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  13. Truncated disc and X-ray spectral states 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)

  14. Truncated disc and X-ray spectral states Geometry of the truncated disc activeregion jet accretiondisc hot innerflow black hole outflow

  15. Truncated disc and X-ray spectral states Spectral states – moving truncation radius Lh/Ls hard state soft state hard state soft state

  16. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  17. Truncated disc and X-ray spectral states 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

  18. Truncated disc and X-ray spectral states Power spectra Quasi-periodic oscillations (QPOs) – unlike, e.g., pulsations, they are not coherent

  19. Hard state – disc is truncatedlower frequencies Truncated disc and X-ray spectral states 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

  20. Truncated disc and X-ray spectral states 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 Soft Hard Di Matteo & Psaltis (1999)

  21. RLSO Rtrunc P Frequency Truncated disc and X-ray spectral states Propagation of fluctuations – broad band PDS

  22. RLSO Rtrunc Truncated disc and X-ray spectral states Propagation of fluctuations – broad band PDS P Frequency

  23. RLSO Rtrunc Truncated disc and X-ray spectral states Propagation of fluctuations – broad band PDS P Frequency

  24. Rtr Truncated disc and X-ray spectral states Behold the last stable orbit Done, Gierliński & Kubota 2007 XTE J1550–564 RLSO • Hard-to-soft transition: decrease truncation radius, increase frequencies • The disc: high-pass filter • Last stable orbit: low-pass filter

  25. Truncated disc and X-ray spectral states Hard-to-soft transition XTE J1650–500

  26. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  27. Truncated disc and X-ray spectral states Accretion disc at low luminosities (< 0.03 LEdd) • Accretion rate  • Truncation radius  • Seed photon input  • Lh/Ls • Spectrum softens Luminosity Ibragimov et al. 2005

  28. soft Reflection amplitude hard Spectral index Truncated disc and X-ray spectral states Accretion disc at low luminosities (< 0.03 LEdd) • Accretion rate  • Truncation radius  • Disc irradiation  • Reflection from the disc  Luminosity Ibragimov et al. 2005

  29. Truncated disc and X-ray spectral states Accretion disc at low luminosities (< 0.03 LEdd) • Accretion rate  • Truncation radius  • Timescales  • QPO frequency  Luminosity hard Spectral hardness soft QPO frequency Axelsson et al. 2005

  30. Truncated disc and X-ray spectral states Accretion disc at low luminosities (< 0.03 LEdd) • Accretion rate  • Truncation radius  • High-pass filter  • Power spectrum narrows Luminosity hard soft Gierliński, Done & Kubota 2007

  31. Truncated disc and X-ray spectral states 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

  32. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  33. Truncated disc and X-ray spectral states 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? GX 339-4 Prominentdisc after Miller et al. 2006

  34. Truncated disc and X-ray spectral states 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) GX 339-4 Prominentdisc after Miller et al. 2006

  35. Truncated disc and X-ray spectral states Soft excess above the disc Cyg X-1 GX 339-4 Cyg X-1 Disc Soft excess Soft excess Brokenpower law Wilms et al. 1999 (ASCA)Broken power law to account for the soft excess 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

  36. Truncated disc and X-ray spectral states 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

  37. Truncated disc and X-ray spectral states 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? hard soft Disc radius (arbitrary units) Gierliński, Done & Page 2008

  38. Outline X-ray spectral states Hard state and Comptonisation Geometry of the accretion flow Variability Truncated disc model Potential problem: strong disc in the hard state Solution: irradiated disc model Conclusions

  39. Truncated disc and X-ray spectral states 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 Lrep LComp Gierliński, Done & Page 2008

  40. Intrinsic discemission Effect ofirradiation 0.1 Truncated disc and X-ray spectral states 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 Lrep LComp Gierliński, Done & Page 2008

  41. hard soft standard disc irradiated disc standard disc irradiated disc with nostress-free boundarycondition irradiated disc irradiated disc with nostress-free boundarycondition Disc radius hard soft Truncated disc and X-ray spectral states Effect of irradiation on disc radius XTE J1817-330 • 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

  42. Truncated disc and X-ray spectral states 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

  43. Truncated disc and X-ray spectral states Fit the UV data (Swift UVOT+XRT) Gierliński, Done & Page 2008 XTE J1817-330

  44. Truncated disc and X-ray spectral states 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 ~ 710-3 • Increased vertical size of corona? • Contribution from jet? hard Irradiation fraction soft transition Comptonisation-to-disc ratio Gierliński, Done & Page 2008

  45. Truncated disc and X-ray spectral states 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

  46. DISC WARS DISC WARS TRUNCATED DISC THE STRIKES BACK 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. WRITTEN BYMAREK GIERLIŃSKIANDCHRIS DONE 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. SPONSORED BY THE MINISTRY OF EDUCATIONOF POLAND X-RAY SATELLITESPROVIDED BYNASA & ESA PERFOMED BYMAREK GIERLIŃSKI PICTURES BYMAREK GIERLIŃSKI COMMISSIONED BYJURI POUTANEN MUSIC THE DEAFS DURHAM UNIVERSITY PRODUCTION

  47. Truncated disc and X-ray spectral states Broad line in GX 339-4? • Diskbb + power law + Laor line fit gives line with Rin= 40.4Rg(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  3Rgwith good models or 4 0.4Rg 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

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