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X-ray emission and reprocessing in AGN

X-ray emission and reprocessing in AGN. Giorgio Matt (Dipartimento di Fisica, Università Roma Tre, Italy). Plan of the talk. Innermost regions of the accretion disc: emission and reprocessing X-ray reprocessing from the pc-scale torus

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X-ray emission and reprocessing in AGN

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  1. X-ray emission and reprocessing in AGN GiorgioMatt (Dipartimento di Fisica, Università Roma Tre, Italy) The Central Engine of AGN - Xi'an

  2. Plan of the talk • Innermost regions of the accretion disc: emission and reprocessing • X-ray reprocessing from the pc-scale torus • Beyond the nucleus: absorption in Compton-thin AGN The Central Engine of AGN - Xi'an

  3. X-ray emission The standard explanation for the X-ray emission is Comptoni-zation of soft (disc?) photons by hot (T=100-200 keV) electrons in a corona (Haardt & Maraschi 1991). The resulting spectrum is, in the first approximation, a power low with a high energy cutoff, as observed (e.g. Perola et al. 2002, Petrucci et al. 2001) Unfortunately, not very much is known on the origin and nature of the corona. Magnetic flares? Clumpy discs? Aborted jets? We do not have the answer yet UV The Central Engine of AGN - Xi'an

  4. Magnetic flares Magnetic flares above the accretion disc is a popular explanation for the heating of the electrons, in analogy with the solar corona. Even if the physical details are rather unclear, MFs are a reasonable working hypothesis to model X-ray spectra and variability (Haardt et al. 1994, Czerny et al. 2004, Goosmann et al. 2006, see also poster 174 by Goosmann). The possible evidence for hot spots (Dovciak et al. 2004) may support this scenario SOHO The Central Engine of AGN - Xi'an

  5. Clumpy discs An old idea (Gilbert & Rees 1988), pursued by many groups over the years (e.g. Celotti et al.1992, Collin et al. 1996, Krolik 1998, Malzac & Celotti 1992, Merloni et al. 2006). Disc instabilities may lead to an inhomogeneous two-phase structure, one hot and optically thin, the other cold and optically thick. Merloni et al. (2006) The Central Engine of AGN - Xi'an

  6. Aborted jets First proposed by Henry & Petrucci (1997). Ghisellini, Haardt & Matt (2004) proposed a model in which blobs are launched with a velocity smaller than the escape velocity. Collisions between the outcoming and returning blobs provide the heating The Central Engine of AGN - Xi'an

  7. X-ray reprocessing X-ray illumination of cold matter produces the so-called ‘Compton reflection’ continuum plus several fluorescent lines, by far the most important being the Fe Kα (e.g. Matt et al. 1991, George & Fabian 1991) (Reynolds et al. 1995) The Central Engine of AGN - Xi'an

  8. Iron lines If reprocessing occurs in the accretion disc, SR and GR effects modify the line profile in a characteristic and well-recognizable way (Fabian et al. 2000) The Central Engine of AGN - Xi'an

  9. (Matt et al. 1992) Iron lines i=20 i=50 i=87 a=0 a=1 Fabian et al. (2000) Isotropic illumination (e.g. George & Fabian 1991, Matt et al. 1991, 1992) The Central Engine of AGN - Xi'an

  10. ASCA (Tanaka et al. 1995) Observations MCG-6-30-15 a>0 !!! BeppoSAX (Guainazzi et al. 1999) XMM-Newton (Wilms et al. 2001) The Central Engine of AGN - Xi'an

  11. How common are relativistic lines in AGN ? XMM-Newton observations of many other bright Seyfert galaxies, however, found only the narrow line (which is almost ubiquitous) (e.g. Pounds & Reeves 2002, Bianchi et al. 2004) MCG-8-11-11 (Matt et al. 2005) The relativistic line is certainly not ubiquitous, at least in nearby Seyfert galaxies. The Central Engine of AGN - Xi'an

  12. Next questions therefore are: • How frequent are the relativistic lines in AGN? • Is the presence of a rel. line related to other AGN properties? Guainazzi et al. (2006) started to address these questions by analysing all radio-quiet, unobscured (or moderately obscured) AGN publicly available in the XMM-Newton archive. The sample is composed of 102 sources.Only a handful of them, however, are bright and well-exposed enough to permit to search for a relativistic line. The Central Engine of AGN - Xi'an

  13. How common are relativistic lines in AGN ? The fraction of sources with a relativistic line in the subsample of sources with enough counts (10000) is: 42 ± 13 % Hopefully, before the end of the mission, we will have enough sufficiently exsposed sources from an unbiased sample to significantly improve this measure. This number is very important to address the question of if and how the standard picture ought to be modified. The Central Engine of AGN - Xi'an

  14. In the meantime, further information can be obtained from stacked spectra. A strong L-dependence is found!! L1: Lx<1043 L2: 1043 <Lx< 5x1043 L3: 5x1043 <Lx<1.5 x1044 L4: Lx> 1.5x1044 The Central Engine of AGN - Xi'an (Guainazzi et al. 2006)

  15. A difference between type 1 and 2 objects seems to be present. If real, is it an inclination effect? Is the disc co-aligned with the absorbing matter , whatever this matter is (the torus, the Galactic disc, etc…)? (Guainazzi et al. 2006) The Central Engine of AGN - Xi'an

  16. Why are rel. lines not ubiquitous? Relatvistic lines are expected in the standard accretion disc scenario, so the fact that they are not always present poses a problem. A few possible solutions (none fully satisfactory): a) Ionized discs b) Truncated discs c) Very broad lines (extreme Kerr) The Central Engine of AGN - Xi'an

  17. Ionized discs Hydrostatic equilibrium (Nayakshin & Kallman 2001) Costant density model (Matt et al. 1996) For a given BH mass, ξ increases with the accr. rate, hence with L. But for a given L/Ledd, ξ decreases with M, then with L!! The Central Engine of AGN - Xi'an

  18. Truncated discs Accretion discs are believed to be truncated in the low/hard state of Galactic BH systems (Fender et al. 2004) (but the issue is still controversial, Miller et al. 2006) It has sometimes been suggested that ‘normal’ Seyfert Galaxies are the analogue of hard state GBH (NLSy1 being possibly the analogue of soft state GBH). But this issue is also highly controversial (e.g. Uttley & McHardy 2005) Recently, we have found possible evidence for disc truncation in a quasar, Q0056-383 (Matt et al. 2005) The Central Engine of AGN - Xi'an

  19. Q0056-383 Q0056-383 was observed twice by XMM-Newton, about 3 years apart. In the second observation, the soft X-ray emission is fainter, the hard X-ray emission is flatter, the iron line EW is halved. Is the disc truncated !?! (Matt et al. 2005) The Central Engine of AGN - Xi'an

  20. Extreme Kerr lines Let us assume that emission comes from very close to the BH. This is possible if the primary X-ray source is close to the event horizon (Martocchia & Matt 1996, Martocchia et al. 2002) In this case, lines are very broad and difficult to separate from the continuum. Their EW are also very large, however, because of light bending and gravitational redshift of the primary emission (Martocchia & Matt 1996, Miniutti et al. 2003) XMM-Newton observations of MCG-6-30-15 have confirmed the presence of the relativistic line, and have shown that the BH is spinning (Wilms et al. 2001, Fabian et al. 2002). First evidence for a spinning BH in a radio-quiet AGN (Fabian et al. 2002) The Central Engine of AGN - Xi'an

  21. Let us assume a ‘lamppost’ on the BH axis, as in the aborted jet model (Ghisellini, Haardt & Matt 2004) (Martocchia & Matt 1996) (Iwasawa et al. 1996) Upper limits on extreme Kerr lines (Bianchi et al. 2004) generally rule out this solution, at least for BL Seyfert 1s, even if such an extreme line has already been observed in a deep low state of MCG-6-30-15 The Central Engine of AGN - Xi'an

  22. Light bending model Indeed, Miniutti et al. (2004) explain the puzzling temporal behaviour of MCG-6-30-15 (the line varies much less than the power law) in terms of an X-ray source close to the BH rotation axis with a variable height (the so called light bending model). They showed that in this model the primary emission varies more than the reprocessed emission The Central Engine of AGN - Xi'an

  23. Polarization of reflected radiation In this scenario, the polarization degree and angle of the reflected radiation strongly depend on h, and hence on time. X-ray polarization is a powerful tools to probe strong gravity. Sensitive enough X-ray polarimeters do exist!!! (Costa et al. 2005) The Central Engine of AGN - Xi'an (Dovciak, Karas & Matt 2004)

  24. Obscuration in AGN The Central Engine of AGN - Xi'an Malkan et al. 1998

  25. Obscuration and reprocessing from cold distant matter I will call “Torus” the circumnuclear, pc-scale matter, whatever its real shape (not necessarily doughnut-like!). (Matt, Guainazzi & Maiolino 2003) >1024 There is increasing evidence that the Torus is Compton-thick, the Compton-thin absorbers probably related to more distant matter. 1023 1022 The Central Engine of AGN - Xi'an

  26. Is the torus C-thick? We analysed 8 Sey1s/C-thin Sey2s observed simultaneously by XMM-Newton and BeppoSAX (Bianchi et al. 2004). In 7 sources there are both a narrow (and constant) iron line and the Compton reflection (CR) continuum C-Thick Torus In the last source (NGC 7213) there is no CR and the line may be produced either in a C-thin torus or in the BLR In many (most?) C-thin Sey2s there is also evidence of reflection by C-thick matter. Evidence come either from broad band spectroscopy or from variability The Central Engine of AGN - Xi'an

  27. Example: NGC 5506 NGC 5506 is a C-thin Sey2 (NH~1022 cm-2 ) with : A narrow (σ<40 eV) iron line Chandra (Bianchi et al. 2003) The Central Engine of AGN - Xi'an

  28. Example: NGC 5506 NGC 5506 is a C-thin Sey2 (NH=1022 cm-2 ) with : a constant Fe line (despite large continuum variations) (Bianchi et al. 2003) The Central Engine of AGN - Xi'an

  29. Example: NGC 5506 NGC 5506 is a C-thin Sey2 (NH=1022 cm-2 ) with : a strong Reflection Component XMM and BeppoSAX (Matt et al. 2001) The Central Engine of AGN - Xi'an

  30. How many Compton-thick Sey2 are there? If the C-thin matter is not the torus, we cannot use the fraction of Sey2 to derive the torus opening angle. We need to look directly at X-ray absorption. In the local Universe, about half of optically selected Sey2s are C-thick To go beyond the local Universe, sensitive (imaging) hard X-ray detectors are needed  SIMBOL-X (Guainazzi, Matt & Perola 2005) (Risaliti et al. 1999) The Central Engine of AGN - Xi'an

  31. How many Compton-thick Sey2 are there? “Elusive” (i.e. without optical evidence of nuclear activity) AGN may account for almost half of local AGN. Most of them are C-thick (Maiolino et al. 2003) The Central Engine of AGN - Xi'an

  32. The X-ray Baldwin effect Iwasawa & Taniguchi (1993), using GINGA data, found an anticorrelation between the EW of the iron line and the X-ray luminosity (called “X-ray Baldwin effect”). The spectral resolution of GINGA was insufficient to separate broad and narrow lines. Page et al. (2004) confirmed this effect using narrow (torus?) lines from XMM-Newton observations of both RQ and RL objects. Jimenez-Bailon et al. (2005) analysed a sample of PG quasars and found that the effect is statistically significant only when RL objects are included. Jiang et al. (2006, see also poster 070), using Chandra and XMM data, found instead a (weaker) effect also for RQ sources only. Bianchi et al. (2006; see also poster 002) analysed all the RQ AGN publicly available in the XMM-Newton archive (130 objects). The Central Engine of AGN - Xi'an

  33. The X-ray Baldwin effect log(EW)=(1.71±0.01)+ (-0.18±0.01)log(Lx) Bianchi et al. (2006; see also poster 002) Possible explanations are: a) Variability (Jiang et al. 2006). It certainly explains part of the effect, but unlikely one spread over several decades in L. b) Decreasing of the covering factor of the torus with L (dust sublimation? Ionization?) The Central Engine of AGN - Xi'an

  34. Where is the C-thin absorber? The C-thin absorbing matter may be the galactic disc (Maiolino & Rieke 1995), or the dust lanes (Malkan et al. 1998, Matt 2000), or starburst regions (Weaver 2001) However, in a few cases (NGC 3227, Lamer et al. 2004; NGC 4388, Elvis et al. 2004, NGC 1365, Risaliti et al. 2005, and the classical case of NGC 4151), the C-thin absorber varies on short time-scales, implying much smaller distances. BLR ? NGC 4388 (Elvis et al. 2004) NGC 1365 (Risaliti et al. 2005) The Central Engine of AGN - Xi'an

  35. Beyond the nucleus. Absorption in Compton-thin AGN Ueda et al. (2003) and La Franca et al. (2005) have found that the fraction of absorbed AGN decreases with X-ray luminosity. These results refer mainly to C-thin AGN, as C-thick AGN are rare in <10 keV surveys. As said before, it is likely that the C-thin absorption is not related to the torus So we (Lamastra, Perola & Matt 2006, see also poster 075) searched for a solution related to the host galaxy. La Franca et al. 2005 The Central Engine of AGN - Xi'an

  36. Beyond the nucleus. Absorption in Compton-thin AGN The inner molecular galactic disc is affected by the gravitational forces of the disc itself, of the Black Hole, and of the Bulge (which in turn depends on the BH mass). The height of the disc, Z(r), then depends on the BH mass, as well as the opening angle (and then the obscuration) Lamastra et al. (2006) The Central Engine of AGN - Xi'an

  37. Beyond the nucleus. Absorption in Compton-thin AGN Assuming L=0.1xLedd, a good agreement with the data is obtained for Σ > 150-200 MΘ/pc2,. Note that Σ=500 MΘ/pc2 in the Galaxy, and that half of sources in the BIMA sample (Helfer et al. 2003) have Σ > 150 MΘ/pc2 Lamastra et al. (2006) The Central Engine of AGN - Xi'an

  38. Summary • Relativistic lines are present in some (40% ??) AGN, but not in all. Still an open problem. • The torus is likely C-thick. Possible dependence of its covering factor on X-ray luminosity (X-ray Baldwin effect) • C-thin absorption likely unrelated to the torus, and possibly related to the host galaxy. The Central Engine of AGN - Xi'an

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