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Flat Radio Sources. Almost every galaxy hosts a BH. 99% are silent 1% are active 0.1% have jets. No lobes. Radio lobes. Broad emission lines. No or weak lines emission lines. Weak FRI radio-galaxy. Powerful FRII radio-galaxy. Radio-galaxies & Blazars.

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slide2

Almost every galaxy hosts a BH

99% are silent

1% are active

0.1% have jets

slide3

No lobes

Radio lobes

Broad emission lines

No or weak lines emission lines

Weak FRI radio-galaxy

Powerful FRII radio-galaxy

radio galaxies blazars
Radio-galaxies & Blazars

FR II poweful radio galaxy, with lobes

FSRQs= Flat Spectrum Radio Quasars, with broad lines

BL Lacs= less powerful, no broad lines

FR I: weak radio galaxy, no lobes

102-103 Rs

slide5

Radio VLBI

Optical HST

Superluminal motion

slide7

Blazars: Spectral Energy Distribution

Radio IR Opt UV X MeV GeV

Inverse Compton

(also possible

hadronic models)

Synchro

slide8

The“blazarsequence”

FSRQs

CT

BL Lacs

LBL and HBL

AGILE GLAST

Fossati et al. 1998; Donato et al. 2001

gamma ray blazars

EGRET: ~100 blazars

Cherenkov: ~40 blazars (a few Radiogal)

Gamma-ray blazars

Fermi

The Universe becomes opaque at z~0.1 at 1TeV at z~2 at 20 GeV

HESS+ MAGIC

slide10

9 years of EGRET (0.1-10 GeV)

Fermi first light, 96 hrs of integration

After 11 months:

~700 (blazars, FSRQsand BL Lacs in equal number)

A few radiogalaxies

4 NLSy1

Starburst galaxies

slide14

TeV BL Lacs

Fermi 1 yr 5s

Tagliaferri et al. + MAGIC, 2008

slide15

No BLR No IR Torus

Weak cooling Large g

G~ 3

G~50

ADAF? L< 10-3 LEdd?

slide16

Emission Models

Simplest scenario: SSC model

No external radiation

slide17

Log N(g)

g-n1

gb

Log g

Log nL(n)

ns

n-a1

n-a2

Log n

The simplest model

R

g-n2

B

G

e

q

slide18

Log N(g)

Log Usyn(n)

+

gb

n1

n’ s

a1

n2

a2

Log g

Log n

Log nL(n)

ns

nC

a1

a1

a2

a2

Log n

The simplest model

slide19

Log N(g)

Log Usyn(n)

gb

n1

n’ s

a1

n2

a2

Log g

Log n

Log nL(n)

nC

ns

a1

aKN

a1

a2

Log n

The simplest model

+

“Klein-Nishina regime”

h n’ s g b >mec2

slide20

SSC model: constraining the parameters

In the simplest version of the SSC model, all the parameters can be constrained by quantities available from observations:

7 free parameters

Model parameters: R B Nogb n1 n2 d

Observational parameters: ns LsnC LC tvar a1 a2

7 observational quantities

Tavecchio et al. 1998

slide21

K

K2

slide22

d4

d4

d

d

slide24

SX 104 s

Data: Fabian+ 2001

slide25

1/2

1/2

RBLR ~ Ldisk

 UBLR= const

RTorus~ Ldisk

 UIR= const

LB ~ B2R2G2c= const  B~1/(RG)

Torus ~1-10 pc

BLR ~0.2 pc

slide26

Torus ~1-10 pc

?

?

BLR ~0.2 pc

slide27

Importance of g-rays

If blob too close to disk, or too compact, AND if emits g-rays, then many pairs

If blob too large (too distant) tvar too long

Then: Rdiss ~ 1000 RS

Energy transport in inner jet must be dissipationless

slide29

Log N(g)

n’o

gb

n1

n2

G2

G

Log g

Log nF(n)

ns

nC

a1

a1

a2

a2

Log n

The simplest model - 5

Log nUext(n)

Broad line region,

Disk

+

no

Log n

slide30

The simplest model - 6

EC + SSC

3C 279

Ballo et al. 2002

B =0.6 - 0.5 d = 17.8- 12.3 gb =550 - 600

slide31

A text-book jet

Torus ~8 pc

CMB

  • B propto 1/R
  • n propto 1/R2
  • M=109Mo
  • Ldisk~LEdd
  • z=3

BLR ~0.3 pc

slide32

1

SX 105 s

0.1 pc

1

slide33

2

1 pc

2

slide34

3

10 pc

3

slide35

4

100 pc

4

slide36

5

1 kpc

5

slide39

n0

SX 105 s

100 kpc

7

10 kpc

6

1 kpc

5

100 pc

4

10 pc

3

2

1 pc

0.1 pc

1

slide40

n0

SX 105 s

100 kpc

7

10 kpc

6

Peak at ~ 100-500 keV

Hard X-rays and GeV: same component (tvar~0.5-1 day)

Soft X-rays: contributions from larger regions, but within 10 pc (tvar<2.5 months)

1 kpc

5

100 pc

4

10 pc

3

2

1 pc

0.1 pc

1

slide42

By modeling, we find physical parameters in the comoving frame.

gpeak is the energy of electrons emitting at the peak of the SED

EGRET blazars

Ghisellini et al. 1998

slide43

Low power slow cooling large gpeak

Big power fast cooling small gpeak

slide44

g-ray emission from non-blazar AGNs

Only one non–blazar AGNs is known at VHE band:

the radiogalaxy M87

slide45

Emission region?

Large scale jet

Stawarz et al. 2003

Knot HST-1 (60 pc proj.)

Stawarz et al. 2006

Cheung et al. 2007

Misaligned (20 deg) blazar

Georganopoulos et al. 2005

Lenain et al. 2007

FT and GG 2008

BH horizon

Neronov & Aharonian 2007

Rieger & Aharonian 2008

slide46

Core?

Acciari et al. 2008

slide47

spine

layer

Ghisellini Tavecchio Chiaberge 2005

Tavecchio & Ghisellini 2008

more seed photons for both
More seed photons for both
  • Grel= GlayerGspine(1-blayerbspine)
  • The spine sees an enhanced Urad coming from the layer
  • Also the layer sees an enhanced Urad coming from the spine

The IC emission is

enhanced wrt to the

standard SSC model

slide49

BL Lac

Radiogalaxy

slide54

Evidences for relativistic beaming

Superluminal motions

Level of Compton emission

High brightness temperatures

Gamma-ray emission/absorption (see below)

slide55

Blazar (BL Lac [no BL],FSRQ [BL])

Radiogalaxy (FRI, FRII),

SSRQ

“Unification scheme”

  • Blazar characteristics:
  • - Compact radio core, flat or inverted spectrum
  • - Extreme variability (amplitude and t) at all frequencies
  • High optical and radio polarization
  • FSRQs: bright broad (103-104 km/s) emission lines
  • often evidences for the “blue bump” (acc. disc)
  • BL Lacertae: weak (EW<5 Å) emission lines
  • no signatures of accretion

Urry & Padovani 1995

Narrow Line Region

Broad Line Region

Obscuring torus (hot dust)

Accretion flow/disk (T~1e4 K)

BH

slide56

The radio-loud zoo is large and complex

Messy classification!FRI, FRII, NLRG, BLRG,

FSRQ, OVV, HPQ, BL Lac objects …

Idea:

Jet emission is anisotropic (beaming): viewing angle

+

intrinsic jet (and AGN) power

slide57

e.g. Ferrarese & Ford 2004

Almost all galaxies contain a massive black hole

99% of them is (almost) silent (e.g. our Galaxy)

1% per cent is active (mostly radio-quiet AGNs):

BH+accretion flow (disk): most of the emission in the UV-X-ray band

0.1% is radio loud: jets mostly visible in the radio

slide61

VHE emission of M87

t var ~ 2 days !

Light curve

Spectrum

slide62

Mkn 501

PKS 2155-304

Aharonian et al. 2007 - H.E.S.S.

Albert et al. 2007 - MAGIC

New problems: Ultra-rapid variability

slide63

Rees 1978 for M87

Observed time: (R0/c)G2(1-bcosq) ~ R0/c !

slide64

tvar =200 s

In the standard scenario tvar>rg/c = 1.4 M9 h!

Conclusion:

only a small portion of the jet (and/or BH horizon)

is involved in the emission

(e.g. Begelman, Fabian & Rees 2008)

slide65

Possible alternative: VHE emission from a fast, transient “needle” (Ghisellini & Tavecchio 2008)

VHE emission dominated by IC from the needle (spine) scattering the radiation of the jet (layer)

A different “flavour” of the spine-layer scenario

slide66

Jet - needle

GG & FT 2008

slide67

Suggested readings

Black holes in galaxies: Ferrarese & Ford 2004, astro-ph/0411247

BH in AGNs: Rees 1984, ARAA, 22, 471

Blandford 1990, Saas Fee Course 20

Krolik, “AGNs”, 1999, Princeton Univ. Press

Beaming: Ghisellini 1999, astro-ph/9905181

Unification schemes: Urry & Padovani 1995, PASP, 107, 803

Emission Mechanisms: Rybicki & Lightman, 1979, Wiley & Son

Jets: Begelman, Blandford & Rees, 1984, Rev. Mod. Physics, 56, 255

de Young, The physics of extragal. radio sources, 2002, Univ. Chicago Press

VHE emission: Aharonian, VHE cosmic gamma radiation, 2004, World Scientific

SSC: Tavecchio, Maraschi Ghisellini, 1998, ApJ, 509, 608

slide69

threshold

g

x2

q

x1

g

Photon-photon pair production in a nutshell

In astrophysical environments g-rays are effectively absorbed through

g + g -> e+ + e-

Rule of thumb:

In isotropic rad. fields, with declining spectra:

slide70

Without any correction:

t (x)= sggR n(1/x) 1/x ~ (1/x)-a ~ xa increasing with E (x=E/mc2)

where n(1/x) 1/x ~ L (1/x) / R2

t (100 GeV)>>1 g-rays cannot escape!!

Internal opacity: limit on d

Observations of gamma rays provide interesting limits on the minimum value of the Doppler factor

Eg=10-100 GeV hn=5-50 eV (UV photons)

slide71

Internal opacity: limit on d

e.g. Ghisellini & Dondi 1996

Taking into account relativistic motion:

1) Intrinsic energy of gamma-ray is lower: decreasing number density of target photons

2)Density of target soft photons also strongly decreases (lower luminosity, larger radius)

t‘ (x)= t(x)/d4+2a

One can find:

Therefore : d > t (x)1/(4+2a)

Typically d>5

slide74

Intergalactic absorption

For TeV blazars the parameters also depends

on the intergalactic absorption correction

(Stecker et al. 1992).

Values of delta up to 50 are obtained

(Krawczynski et al. 2002, Konopelko et al. 2003)

The correction is uncertain: deconvolved TeV

spectral shape can be used to discriminate

between different possibilities

Problem and opportunity at the same time!

slide75

Extragalactic background light

EBL measurements

Dust

Starlight

Mazin & Raue 2007

slide76

3C 273

Mkn 501

M87

Cen A

Coppi & Aharonian 1997

The “g-ray horizon”

Mean free path

slide77

Aharonian et al. 2006: even with the lowest IR background the de-absorbed spectrum is very hard (photon index=1.5).

Large EBL

MediumEBL

MinimumEBL

slide78

However, harder intrinsic spectra

can be obtained assuming a power law

electron distribution with a

relatively large lower limit gmin

Synchrotron

Below the corresponding freq.

synchrotron and SSC spectra

are very hard!

Katarzinski et al. 2006

SSC

The absolute limit is:

Fn ~ n1/3

slide80

B2

~B (Klein Nishina

B

slide83

L=L’d4

n=n’ d

Dt=Dt’/d

G

Special relat.

q

1

d =

G (1-b cos q)

Photon “compression”

The relativistic Doppler factor

slide84

gb

gb (Klein Nishina)

gb

gb2

slide86

Constraints from 3C279

Albert at al. 2008

slide87

VHE emission of FSRQs

3C 279, z=0.536

Albert at al. 2008

slide88

The future -2

New Cherenkov Telescope Arrays:

?

AGIS, USA

CTA, Europe

slide89

Rees 1978 for M87

Observed time: (R0/c)G2(1-bcosq) ~ R0/c !

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