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Unraveling X-ray Reflection Spectra: Prospects for Understanding Accreting Black Holes

This presentation by Giovanni Miniutti from the Institute of Astronomy, University of Cambridge, discusses the complexities of X-ray reflection spectra from accreting black holes (BHs). Focusing on the spectral components, including soft excess, power law, and reflection effects, the talk highlights observational challenges caused by superimposed reflection spectra from distant and nearby sources. It emphasizes the need for advanced observational techniques like SIMBOL-X to better understand the inner accretion flows and their implications for black hole physics.

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Unraveling X-ray Reflection Spectra: Prospects for Understanding Accreting Black Holes

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  1. The X-ray mirrors • Giovanni Miniutti • Institute of Astronomy, University of Cambridge SIMBOL-X - 2007 May -Bologna

  2. Accreting BHs: main spectral components Soft excess Power law X-ray reflection e.g. Fabian & Miniutti (CUP, in press) • all modified by absorption (Galactic and/or intrinsic)

  3. The X-ray reflection spectrum PLC RDC Reynolds 96

  4. X-ray reflection: relativistic effects Doppler shifts relativistic beaming Fe K gravitational redshift intensity gravitational light bending e.g. Fabian, Rees, Stella & White 89

  5. X-ray reflection: two mirrors • The same reflection model in the rest frame (e.g. from distant matter) • and as observed if reflected from the inner accretion disc

  6. X-ray reflection: two mirrors torus disc • The observational challenge is that the two reflection spectra are ususally superimposed and it becomes difficult to disentangle

  7. X-ray reflection: two mirrors • In principle, the contribution from the distant (torus) and closeby (disc) • mirrors can be disentangled via the Fe K line profile • However, this is possible only in a limited number of sources • mainly because the broad component is often undetected which suggests • either that the broad line is absent (e.g. disc too ionized) or that • the broad line it is lost into the continuum • In typical exposures with limited band pass (e.g. XMM, Chandra) a typical disc reflection component and broad Fe line are indeed very easy to miss • This means that we are still unableto understand the nature geometry and physical state of the inner flow in a large population via Fe line diagnostics

  8. X-ray reflection: observational bias

  9. … does not have any disc • reflection component ! • … too difficult to detect. X-ray reflection: observational bias • A typical 40 ks XMM exposure • assuming the composite model • but the best-fitting model ….

  10. X-ray reflection: observational bias • Thus, a typical X-ray disc reflection spectrum (Afe~1; R~1) is challenging to detect in a typical ~40ks XMM observation • The best disc reflection examples are associated with peculiar conditions, in particular: • Fe overabundance • Higher (than expected) reflection fraction • which suggests that the relatively low statistics of secure broad Fe lines and disc reflection spectra is affected by an observational bias • A larger effective area at ~6keV is important (e.g. XEUS) to disentangle between narrow and broad Fe line components, but extending the band pass to higher energies is a fundamental and crucial step to have a better understanding of the inner accretion flow

  11. The best case so far Fabian et al 02 Tanaka et al 95

  12. The Suzaku mission • Observed during the SWG phase (about 350 ks) Miniutti et al PASJ 07

  13. (c) A. Bamba The Suzaku mission • Observed during the SWG phase (about 350 ks) Miniutti et al PASJ 07

  14. The Suzaku mission

  15. The Suzaku mission

  16. The Suzaku mission

  17. The Suzaku mission

  18. The Suzaku mission

  19. The Suzaku mission

  20. Prospects for SIMBOL-X • Simultaneous data in the Fe K band and > 10keV have shown that sensitivity in a wide band pass is able to disentangle the models and reveal with little/no ambiguity not only the presence of disc reflection but also its strength, reflection fraction, ionization state, Fe abundance … • The SIMBOL-X mission will take these studies to a new level allowing us to perform statistical studies which will not be limited to the best cases in which peculiar conditions arise (MCG-6-30-15 has AFe~2-3 and R~2-3) • Thiswill open up a new parameter space to study the geometry and physical state of the inner accretion flow in AGN and X-ray binaries

  21. Prospects for SIMBOL-X

  22. Prospects for SIMBOL-X

  23. Conclusions • The simultaneous presence of (at least) 2 X-ray mirrors • distant (torus) • closeby (disc) • Makes it difficult to interpret the spewctral shape in the Fe K band • Present observatories do not have enough • effective area in the Fe K band • broadband sensitivity (especially > 10keV) • and only reveal disc reflection in a limited number of sources ( obs bias? ) • The advent of Suzaku already showed the potential of > 10keV sensitivity • An advanced mission such SIMBOL-X will be able to unveil the nature of the inner accretion flow in a much large population

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