The X-ray mirrors

Giovanni MiniuttiInstitute of Astronomy, University of Cambridge

SIMBOL-X - 2007 May -Bologna

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)

The X-ray reflection spectrum

PLC

RDC

Reynolds 96

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

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

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

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

X-ray reflection: observational bias

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.

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

The best case so far

Tanaka et al 95

Fabian et al 02

The Suzaku mission

Observed during the SWG phase (about 350 ks)

Miniutti et al PASJ 07

The Suzaku mission

Observed during the SWG phase (about 350 ks)

Miniutti et al PASJ 07

(c) A. Bamba

The Suzaku mission

The Suzaku mission

The Suzaku mission

The Suzaku mission

The Suzaku mission

The Suzaku mission

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

Prospects for SIMBOL-X

Prospects for SIMBOL-X

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