Andrzej A. ZdziarskiCentrum Astronomiczne im. M. Kopernika

Warszawa, Poland

Radiative processes and geometry of accreting

black holes

Spectral states of accreting

black holes

hard

soft

EGRET

GLAST 200 ks

unabsorbed spectra

INTEGRAL

Hard states

Cyg X-1: typical hard state spectrumthermal

Comptonization

Comptonreflection

Fe Kalpha

Gierliński et al. (1997)kTe 100 keV, 1, /2 0.3, L1-2% of LE

Ginga/LACCGRO/OSSE

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

Thermal Comptonization

Seed photons

log

E F

(E)

Energy gain

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.

Lsoft

Comptonized spectrumcutoff: E>kTe

Lhard

No more OSSE spectra available because of the reentry of CGRO in

June 2000:

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

Spectra of GX 339–4 in the hard state

Wardziński et al. (2002)

kTe always ~50–100 keV

Seyferts: NGC 4151 and IC 4329A

Spectra very similar to those of black-hole binaries in the hard state

kTe always ~50–100 keV

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

blackhole

cold outer disk

direct softphotons

scatteredhard photons

reflectedphotons

A likely geometry inferred for the hard state:

hot inner disk

variable inner radius

outflow/jet emitting radio+

A strong correlation between the radio and X-ray fluxes in black hole binaries:

Gallo, Fender & Pooley (2003)

15 GHz

Based on this R-X correlation, nonthermal synchrotron origin of X-rays in the hard state

has been claimed (Markoff et al.)

kTe always ~50–100 keVHowever, 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.

Comptonization fits to Cyg X-1 spectra

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

pairs

no pairs Constant power in the hot plasma,

Lhard, variable seed

soft photons, Lsoft

pivoting.

pivot

pivot

Cyg X-1: hard-state long-term variability:

variable Lsoft

constant Lhard

variable Lsoft

constant Lhard

It also rules out the nonthermal

synchrotron model.

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.”

LIR LX

(Malkan & Sargent 1982; Malkan 1984;

436 citations)

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

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)

Soft states

Cyg X-1: a soft-state spectrum

blackbodydisk emission

hybrid thermal- nonthermal plasma

Compton reflectionfrom an ionized disk

Fe K alpha

Gierliński et al. (1999)

L0.05LE

Radiative processes in the soft state

variable accelerationN() -

variable heating

thermal part

nonthermal part

Compton &Coulomb

> 2: Compton cooling < 2: Coulomb thermalization

A hot, hybrid, plasma

constant soft seed photons

Cold medium

Photon spectrum

The steady-state electron distribution:Maxwellian + a tail

Parameters of the hybrid, thermal/nonthermal, coronal plasma of Cyg X-1:

1996: kTe 60 keV, 0.1, acc 2.5,

Lnth/Lhot0.5, Lhot/Ldisk0.5, /2 1

2002: kTe 20 keV, 1, acc 4,

Lnth/Lhot0.5, Lhot/Ldisk0.5, /2 1

The presence of nonthermal processes required in the soft state

Q() -acc

The physics of acceleration: reconnections, shocks, waves – unknown as yet

A likely geometry inferred for the soft state:

Blackhole

Cold accretion disk

Unstable non-thermal flares Soft seed

photons

Scatteredhard photons

Reflectedphotons

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.

GRS 1915+105: 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

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 1915+105:

LLE

L0.3LE

L0.3LE

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 1915+105

Done 2002

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)

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 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.

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; ...

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.