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IXO and strong gravity Measuring the black hole spin

IXO and strong gravity Measuring the black hole spin. Giorgio Matt (Dipartimento di Fisica ‘Edoardo Amaldi ’, Università degli Studi Roma Tre). The importance of spin measurements. Why is important to know the BH spin distributions?.

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IXO and strong gravity Measuring the black hole spin

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  1. IXOand strong gravityMeasuring the black hole spin GiorgioMatt (Dipartimento di Fisica ‘Edoardo Amaldi’, Università degli Studi Roma Tre)

  2. The importance of spin measurements Why is important to know the BH spin distributions? In AGN, it can discriminate between different growth histories (spin is mainly acquired during the SMBH evolution) In GBHS, it tells us about the origin of the BH (spin is mainly pristine) Berti & Volonteri 2008

  3. Accretion discs Let us assume a geometrically thin, optically thick accretion disc. Matter rotates in (quasi) circular orbits (i.e. Vφ >> Vr ) with Keplerian velocities. We can assume that the inner disc radius corresponds to the innermost stable circular orbit (ISCO) The ISCO depends on the BH spin and on whether the disc is co- or counter-rotating with the BH NB: a≤0.998, RISCO=1.237 (Thorne 1973)

  4. Techniques • (Iron) line spectroscopy (GBH, AGN) • Continuum spectroscopy (GBH) • Timing (GBH, AGN) • Polarimetry (GBH, AGN) NB: All these techniques are (mainly) based on the dependence of ISCO (in units of the gravitational radius) on spin

  5. Why IXO • Large collecting area !!!!!! • All different techniques can be applied thanks to: • Broad band (0.3-40 keV) • Moderate to high spectral resolution • High count rates detector • Polarimetry

  6. X-ray emission The standard explanation for the hard X-ray emission in AGN and GBHS is Comptonization of disc photons by hot (T=100-200 keV) electrons in a corona (e.g. Haardt & Maraschi 1991). The resulting spectrum is, in the first approximation, a power low with a high energy cutoff. In GBHS, the thermal component is also in the X-ray band, extending up to several keV when in soft state. UV/soft X

  7. X-ray emission The standard explanation for the hard X-ray emission in AGN and GBHS is Comptonization of disc photons by hot (T=100-200 keV) electrons in a corona (e.g. Haardt & Maraschi 1991). The resulting spectrum is, in the first approximation, a power low with a high energy cutoff. In GBHS, the thermal component is also in the X-ray band, extending up to several keV when in soft state.

  8. (Fabian et al. 2000) Line profiles SR and GR effects modify the line profile in a characteristic and well-recognizable way a=0 Advantages of the method are: Intrinsic emission is known Independent of the black hole mass (radius is measured in units of the gravitational radius) a=1

  9. ASCA (Tanaka et al. 1995) Observations Rin > 6 MCG-6-30-15 BeppoSAX (Guainazzi et al. 1999) Rin <6, a>0 !!! XMM-Newton (Wilms et al. 2001)

  10. Is MCG-6-30-15 unique ? Iron L line 1H 0707-495 (Fabian et al. 2009)

  11. SWIFT J1247 (Miniutti et al. 2010) Fairall 9 (Schmoll et al. 2010) NB: results obtained by fitting simulateneously the line and the reflection continuum

  12. Observations:GBHC GRS 1915-105 (Martocchia et al. 2002) XTE 1650-500 (Miniutti et al. 2003) GX 339-4 (Miller et al. 2004)

  13. Observations:GBHC Miller et al. 2009 (see also Ng et al. 2010 and Miller et al. 2010)

  14. Continuum spectroscopy Fitting the disc thermal emission provides a measurement of ISCO. Requires: a) Spectrum dominated by thermal emission (soft state) b) A very good modelling of the emission c) Accurate values of M, i, D R RISCO Much work by McClintock, Narayan et al.

  15. Strong dependence on RISCO and thence on the spin 0.10 a* = 0.98 dF/d(lnR) a* = 0.9 0.05 a* = 0.7 a* = 0 0 R/M(G/c2)

  16. Spin Results to Date McClintock et al. (2011)

  17. Different methods give different results… Disk reflection method Thermal continuum method (but recently the results of the two methods on J1550 have been reconciled by Steiner et al. 2010) Miller et al. (2009)

  18. QPOs

  19. Zhang et al. 1998 Stella & Vietri 1998+ The mass of the black hole is needed to derive the spin

  20. Orbiting spots Courtesy of M. Dovciak From time resolved spectroscopy it is possible to derive the radius both in units of the BH mass and in standard units  BH mass (and l.l. to the spin)

  21. Orbiting spots Dovciak et al. 2008

  22. Observations: NGC 3516 Iwasawa et al. (2004) find in the XMM-Newton data of NGC 3516 evidence for a possible 25 ks periodicity of one of these features. The derived BH mass is 1-5 x 107 solar masses consistent with other estimates

  23. Strong gravity effects on polarization General and Special Relativity significantly modifies the polarization properties of the radiation. In particular, the Polarization Angle (PA) as seen at infinity is rotated due to aberration (SR) and light bending (GR) effects (e.g. Connors & Stark 1977; Pineault 1977). The rotation is larger for smaller radii and higher inclination angles (Connors, Stark & Piran 1980) Orbiting spot with: a=0.998; R=11.1 Rg i=75.5 deg (Phase=0 when the spot is behind the BH). Newtonian - - - - - - - - - - - - - - - - - - - - - - - The PA of the net (i.e. phase-averaged) radiation is also rotated!

  24. Galactic BH binaries in high state X-ray emission in Galactic BH binaries in soft states is dominated by disc thermal emission, with T decreasing with radius. A rotation of the polarization angle with energy is therefore expected. GRS 1915+105 (Done & Gierlinski 2004) Connors & Stark (1977)

  25. We (Dovciak et al. 2008) revisited and refined these calculations (see also Li et al. 2008, Schnittman & Krolik 2009). Strongly dependent on the spin of the BH !! (Independent of the black hole mass Detectability of the effect with IXO

  26. GR effects: light bending model Variations of hhave been suggested to be the cause of the puzzling temporal behaviour of the iron line in MCG-6-30-15 (Miniutti et al. 2003), where the line flux varies much less than the primary power law flux. This situation is expected in the aborted jet models for the corona (e.g. Ghisellini et al. 2004). PLC Fe line

  27. Polarization of reflected radiation The polarization degree and angle depend on both h and the incl. angle (the latter may be estimated from the line profile; for MCG-6-30-15 is about 30 degrees, Tanaka et al. 1995) Variation of h with time/flux implies a time/flux variation of the degree and angle of polarization Dovciak et al. 2004, 2011

  28. Polarization of reflected radiation The polarization degree and angle depend on both h and the incl. angle (the latter may be estimated from the line profile; for MCG-6-30-15 is about 30 degrees, Tanaka et al. 1995) Variation of h with time/flux implies a time/flux variation of the degree and angle of polarization Dovciak et al. 2004, 2011

  29. Summary Thanks to the combination of large collecting area and of spectroscopic, timing and polarimetric capabilities, IXO will be able to measure the spin of the black hole in both GBHS and AGN in several different, independent ways.

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