Radiative processes and geometry of accreting black holes

1. Radiative processes and geometry of accreting black holes Andrzej A. Zdziarski Centrum Astronomiczne im. M. Kopernika Warszawa, Poland

2. INTEGRAL EGRET GLAST 200 ks Spectral states of accreting black holes unabsorbed spectra hard soft

3. Hard states

4. thermal Comptonization Fe K alpha Compton reflection Cyg X-1: typical hard state spectrum CGRO/OSSE Ginga/LAC kTe  100 keV,   1, /2  0.3, L1-2% of LE Gierliński et al. (1997)

5. Seed photons for Comptonization: disk blackbody. soft excess main Comptonization An additional soft excess: physical origin remains unknown; it is well fitted by an additional thermal Comptonization component. Cygnus X-1 Frontera et al. (2001); Di Salvo et al. (2001)

6. cutoff: E>kTe Comptonized spectrum Lhard Energy gain Thermal Comptonization Seed photons log E F(E) Lsoft log E The photon index, , is a function of kTe and  (the Thomson optical depth). The parameters found in black holes binaries: kTe  50—100 keV,   1.

7. No more OSSE spectra available because of the reentry of CGRO in June 2000:

8. INTEGRAL & CGRO INTEGRAL observations of Cyg X-1 hard state SPI, rev. 19 ISGRI, rev. 15–18 OSSE, av. 91–94 BATSE, av. 91–94 COMPTEL, av. 91–94 (McConnell et al. 02)

9. Spectra of GX 339–4 in the hard state kTealways ~50–100 keV Wardziński et al. (2002)

10. Seyferts: NGC 4151 and IC 4329A kTealways ~50–100 keV Spectra very similar to those of black-hole binaries in the hard state

11. Ratio of the high-energy spectra of GX 339–4 and NGC 4151 The same shape of the high-energy cutoff Z. et al. (1998)

12. direct soft photons scattered hard photons reflected photons A likely geometry inferred for the hard state: outflow/jet emitting radio+ variable inner radius cold outerdisk hot inner disk black hole

13. A strong correlation between the radio and X-ray fluxes in black hole binaries: 15 GHz Gallo, Fender & Pooley (2003)

14. Based on this R-X correlation, nonthermal synchrotron origin of X-rays in the hard state has been claimed (Markoff et al.) However, the position of the high-energy cutoff of the synchrotron emission is  2B, which is a sensitive function of the source parameters. In the standard shock model, Ecutoff 100(2/) MeV, where  is the shock speed and  is the acceleration efficiency. Thus, fine-tuning is required. Furthermore, the photon index >1.75 in this model, whereas harder spectra are commonly observed. kTealways ~50–100 keV Comptonization fits to Cyg X-1 spectra

15. Another severe problem concerns the shape of the high-energy cutoff. The theoretically predicted cutoff (from synchrotron emission of power law electrons with an exponential cutoff) is notsharp enough. Thus this model is ruled out. Z. et al. 2003 While the hot inner flow may be identical to the base of the jet, the main radiative process in that region is thermal Comptonization, notnonthermal synchrotron.

16. Constant power in the hot plasma, Lhard, variable seed soft photons, Lsoft pivoting. variable Lsoft Cyg X-1: hard-state long-term variability: pivot constant Lhard no pairs variable Lsoft pivot constant Lhard pairs It also rules out the nonthermal synchrotron model.

17. A cautionary tale: an analogous IR–X-ray correlation found in AGNs „Extrapolation of the nonthermal red/infrared power law (which completely dominates the 3.5 m flux) always gives an excellent prediction of the 2 keV flux, regardless of the UV properties of the AGN. The relation is exceedingly well defined since there is so little scatter.” (Malkan & Sargent 1982; Malkan 1984; 436 citations) 3.5 m LIR LX 2 keV

18. This prompted Zdziarski (1986, ApJ, 305,45) to propose a nonthermal, synchrotron-self-Compton AGN model: A variation of this nonthermal model including pairs was later proposed by Zdziarski et al. (1990, ApJ, 363, L1). However, the model was later rejected (e.g. Zdziarski et al. 1994, MNRAS, 269, L55) as it did not account for the high energy cutoff observed by the CGRO/OSSE. Thus, the origin of the IR–X-ray correlation has to be due to something different than emission by the same electrons. the high-energy cutoff observed by OSSE X-rays IR final model spectrum

19. But a possible weak high energy photon tail in the hard state: an electron tail beyond a Maxwellian Johnson et al. (1997) McConnell et al. (2002)

20. Soft states

21. hybrid thermal- nonthermal plasma blackbody disk emission Compton reflection from an ionized disk Fe K alpha Cyg X-1: a soft-state spectrum L0.05LE Gierliński et al. (1999)

22. variable heating nonthermal part thermal part variable accelerationN()  - Radiative processes in the soft state  > 2: Compton cooling  < 2: Coulomb thermalization Photon spectrum A hot, hybrid,plasma Cold medium Compton &Coulomb  constant softseed photons The steady-state electron distribution: Maxwellian + a tail

23. The presence of nonthermal processes required in the soft state Parameters of the hybrid, thermal/nonthermal, coronal plasma of Cyg X-1: 1996:kTe  60 keV,   0.1, acc  2.5, Lnth/Lhot0.5, Lhot/Ldisk0.5, /2  1 2002:kTe  20 keV,   1, acc  4, Lnth/Lhot0.5, Lhot/Ldisk0.5, /2  1 Q()   -acc The physics of acceleration: reconnections, shocks, waves – unknown as yet

24. A likely geometry inferred for the soft state: Scattered hard photons Unstable non-thermal flares Soft seed photons Reflected photons Cold accretion disk Black hole

25. Classification of states: high state vs. very high state: Different amplitudes of the tail. No high-energy cutoff up to at least several MeV in both cases Gierliński & Done (2003)

26. GRS 1915+105: hybrid spectral fits All its states are actually soft: high and very high. Comptonized disk blackbody in this soft/high state Very high state The same model as for Cyg X-1, except that both the disk and corona are unstable because of a much higher accretion rate. RXTE: PCA, HEXTE CGRO/OSSE Z. et al. (2001)

27. Cygnus X-3 – an enigmatic object Neutron star or a black hole? Hints from its broad-band spectra being very similar to GRS 1915+105: Cygnus X-3 LLE L0.3LE L0.3LE

28. What is the origin of the flat (2) power law seen in the disk-dominated states? Cygnus X-3 XTE J1550–564 Done 2002 Also seen in GRS 1915+105

29. What about Narrow-Line Seyfert 1s? The model spectrum of 1H 0707-495 (Leighly et al.) blackbody Comptonization A striking similarity to the soft states of black-hole binaries, noted by Pounds et al. (1995)

30. Z. (1996) emission due to  decay Importance of hadronic processes for MeV emission? Spectrum before pair production effects final model spectrum Bhattacharyya et al. (2003): Comparison of a hadronic model with RXTE/OSSE observations of GRS 1915+105 implies that a nonthermal fraction of protons is small (<5%) and that the power in accelerated electrons is at least an order of magnitude higher than that in accelerated protons.

31. Hysteresis in LMXBs soft-to-hard Hard-to-soft state transitions occur at much higher luminosities than soft-to-hard state transitions. hard-to-soft GX 339–4 modeled by an accretion disk Miyamoto et al.; Maccarone & Coppi; Nowak; ...

32. An overall picture • Thermal Comptonization cutoff seen in both low/hard state of black-hole binaries and in Seyferts (both radio-quiet and radio-loud). • The only strong (i.e. comparable to accretion power) X-ray emission seen from jets as yet is from blazars. No fine-tuning of the high-energy cutoff of nonthermal synchrotron in those objects. • The soft state: importance of nonthermal Comptonization. Probable analogy to NLS1s.