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

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Presentation on theme: "Andrzej A. Zdziarski Centrum Astronomiczne im. M. Kopernika Warszawa, Poland Radiative processes and geometry of accreting black holes."— Presentation transcript:

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

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

3 Hard states

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

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

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

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

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

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

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

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

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

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

14 Based on this R-X correlation, nonthermal synchrotron origin of X-rays in the hard state has been claimed (Markoff et al.) kT e always ~50–100 keV However, the position of the high-energy cutoff of the synchrotron emission is   2 B, which is a sensitive function of the source parameters. In the standard shock model, E cutoff  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. 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 not sharp enough. Thus this model is ruled out. While the hot inner flow may be identical to the base of the jet, the main radiative process in that region is thermal Comptonization, not nonthermal synchrotron. Z. et al. 2003

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

17 A cautionary tale: an analogous IR–X-ray correlation found in AGNs 3.5  m 2 keV „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.” L IR  L X (Malkan & Sargent 1982; Malkan 1984; 436 citations)

18 This prompted Zdziarski (1986, ApJ, 305, 45) to propose a nonthermal, synchrotron-self-Compton AGN model: IR X-rays final model spectrum 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

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

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

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

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

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

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

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

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

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

30 Importance of hadronic processes for MeV emission? final model spectrum Spectrum before pair production effects emission due to  decay Z. (1996) Bhattacharyya et al. (2003): Comparison of a hadronic model with RXTE/OSSE observations of GRS 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 GX 339–4 modeled by an accretion disk hard-to-soft soft-to-hard Hard-to-soft state transitions occur at much higher luminosities than soft-to-hard state transitions. 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.


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