The X-ray mirrors
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Transcript of The X-ray mirrors
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The X-ray mirrors
Giovanni MiniuttiInstitute of Astronomy, University of Cambridge
SIMBOL-X - 2007 May -Bologna
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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)
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The X-ray reflection spectrum
PLC
RDC
Reynolds 96
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X-ray reflection: relativistic effects
Fe K
inte
nsity
Doppler shifts
relativistic beaming
gravitational redshift
gravitational light bending
e.g. Fabian, Rees, Stella & White 89
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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
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X-ray reflection: two mirrors
disc
torus
The observational challenge is that the two reflection spectra are ususally superimposed and it becomes difficult to disentangle
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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 unable to understand the nature geometry and physical state of the inner flow in a large population via Fe line diagnostics
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X-ray reflection: observational bias
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X-ray reflection: observational bias
A typical 40 ks XMM exposureassuming the composite model
but the best-fitting model ….
… does not have any disc reflection component !
… too difficult to detect.
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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 overabundanceHigher (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
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The best case so far
Tanaka et al 95
Fabian et al 02
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The Suzaku mission
Observed during the SWG phase (about 350 ks)
Miniutti et al PASJ 07
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The Suzaku mission
Observed during the SWG phase (about 350 ks)
Miniutti et al PASJ 07
(c) A. Bamba
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The Suzaku mission
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The Suzaku mission
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The Suzaku mission
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The Suzaku mission
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The Suzaku mission
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The Suzaku mission
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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)
This will open up a new parameter space to study the geometry and physical state of the inner accretion flow in AGN and X-ray binaries
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Prospects for SIMBOL-X
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Prospects for SIMBOL-X
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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 enougheffective area in the Fe K bandbroadband 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