24thJune2010 ActiveGalacticNucleiTobiasBeuchert ExtragalacticX-rayandGammasources

Extragalactic X-ray and Gamma sources

Active Galactic Nuclei

Tobias Beuchert

Universität Erlangen-Nürnberg

24th June 2010

1 General Characteristics

2 Classification, Unified Model

3 Energy Gain

4 SED

5 Further Jet Physics

6 research

NGC3783 linear intensity scale NGC3783 logarithmic intensity scale

Wikipedia

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

normal galaxies, e.g. M31 - In- frared:

◮ concentrated thermal emission at IR and optical wavebands

◮ diameter ∼43 kpc

◮ integrated luminosity

∼10^{44 erg}_s AGN:

◮ broad, mainly non-thermal continuum emission

◮ diameter ∼ pc

◮ integrated luminosity

∼10⁴²-10^{48 erg}_s ≈10¹⁰L⊙

0http://nedwww.ipac.caltech.edu/

M31 averaged SED of many blazars

0[5], [3], [10], [15], [18]

0www.astr.ua.edu/keel/agn/

Optical spectrum of the central region of NGC 1068. Fath (1908): comparable to planetary nebula spectra, but with broad emission lines

0[4]

5000 6000 7000 Wavelength [A]

0 1 2 3 4

Flux [arbitrary units] Hα rest

Hβ rest

Hγ rest [O III] rest

5000 6000 7000

Wavelength [A]

0 1 2 3 4

Flux [arbitrary units] Hα, z=0.158

Hβ, z=0.158

Hγ, z=0.158 [O III], z=0.158

Maarten Schmidt (1962): redshift of lines⇒distance using Hubble’s lawv=HD⇒ absolute magnitude over distance modulus⇒luminosity by comparingMabswithM_⊙

⇒Lquasar ≈50·Lbrightest galaxy=4.8·10¹²L_⊙for 3C 273

0[18], Falke (MPIfR), [13]

BLR NLR Sy 1

QSO

Sy 2 QSO

Unified model for radioquiet AGN

0http://www.obspm.fr/actual/nouvelle/jul04

FR 1

BLRG

NLRG

radio loud quasars

FR 2

BLRG

NLRG

radio loud quasars

Unified model for radioloud AGN

FR II Type, Quasar 3C175, VLA image at 6cm

(http://www.cv.nrao.edu/~abridle/3c175.htm)

FR I Type, 3C271.1, M84

(http://nedwww.ipac.caltech.edu/)

0[13]

Which process of gaining energy is the most efficient one?

Nuclear Fusion

E=ǫmc² (1)

L≈10⁴⁷erg/s over 10⁷yrs (≈3.2·10⁶¹erg) requires:

m= E

ǫc^2≈2.2·10

9M⊙ (2)

(1−ǫ)m ⇒“fusion-waste”!

Schwarzschildradius of that mass:

rs=2Gm

c^{2 ≈6.6·10}

12m (3)

→ǫ=0.008 ⇒energy yield≈7.2·10¹⁸erg/g Gravitation ⇒ǫ≈0.1⇒energy yield≈10²⁰erg/g

0[15], [18]

accretion process I

optical thick accretion disc

⇒balance between radiation and gravitation

◮ angular momentum→no accretion

◮ frictional forceF_fr≪Fgrav⇒Kepler orbits

◮ differential rotation⇒heating⇒outward loss of angular momentum⇒accretion Radiation

∆E=GM•m

r ⁻

GM•m r+ ∆r ^≈

GM•m

r^{2 ∆}r (4)

virial theorem:Ekin=−1/2Epot=−1/2∆E

∆E−E_kin=E_i ⇒heating⇒radiation Using[L] =erg/s:

∆L=GM•m˙

2r^{2 ∆}r (5)

with accretion ratem˙.

condition for matter being accreted (optically thick discs) dpgrav

dr

>! dprad

dr ⁽⁶⁾

⇒upper luminosity (Eddington LuminosityL_Edd, see handout) L<^!LEdd=GM•mHc

σT

≈1.3·10³⁸erg/s·M•

M_⊙ ⁽⁷⁾

upper accretion rateM˙_Edd:

LEdd=ηM˙Eddc² (8)

⇒M˙_Edd=L_Edd

ηc^{2 ≈2}M_⊙/yr (9)

With an efficiencyηof>0.12 due to high optical depth as “resistance” for photons.

0[12], [7]

Temperature Profile

Black body radiation (optical thick)→temperature layer with Planck Law

∆L=4πr∆rσT⁴ T(r) = L

4πr³σSB

!−1/4

= GM•m˙ 8πr³σSB

!−1/4

rs=2GM•/c²

= c⁶

64πσSBG²

!1/4

˙ m^1/4M_•^−1/2

r rs

−3/4

(10)

→r fixed,m˙ ↑ ⇒T↑

→M• ↑, reached temperatures↓

0[15]

top: 3C273 in X-Rays (NASA/CXS/SAO, 2003), bottom: Jet of 3C273 in 2cm, VLBA (NRAO, Kellermann 1998)

Spectral Energy Distribution (SED) of 3C273 ([13], p.149)

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

Radio Submillimetre - IR UV X-Ray Gamma

◮ need many instruments on earth and in orbit measuring

“simultaneous” if possible

◮ units:

[S_ν] =erg/m²sHz=W/m²Hz

◮ units:[νS_ν] =W/m²

◮ L=R_ν2

ν₁ S_νdν=R_lnν2

lnν₁ νS_νdlnν

◮ (logS_ν−logν): equal energy at all frequencies→spectrum with α=−1

◮ (logνS_ν−logν): equal energy at all frequencies→flat spectrum with α=0⇒good indicator for above-average flux (bumps...)

◮ overall radiation follows powerlaws likeS_ν∼ν^−α

0[13]

→high degree of linear polarization.

→Electron frame of rest: radial symmetric emission whole emitted power:

I=4

3σTcγ²Umag (11)

“cooling time” (energy decreased by factor 2):

t=3 2

m⁴c⁷ e⁴B²E0

(12)

0http://www.cv.nrao.edu/~abridle/3c175.htm, [13], [7], [11], [2], Falke, [14]

Radio - synchrotron emission (realistic conditions)

less massive particles (electrons)⇒most efficient energy loss⇒seem to form a leptonic plasma

More realistic conditions (see handout):

theoretical model of an AGN

helical trajectory of electrons around H-fieldlines

0[13], [7], [11], [2], [? ]

→ powerlaw-distribution of electrons in jet plasma: N(E)dE∼E^−sdE

gained energy by radiation=lost energy through emission

=particle distribution·synchrotron emission I_νdν=η(E)dE=N(E)dE·dE

dt I_ν∼











B^−1/2ν^5/2 ν < νc synchrotron self absorption

ν^−(p−1)/2 ν > νc optical thin (13)

0[13], [7], [11], [2]

Radio - synchrotron emission (ensemble of electrons)

black body emission at different temper- atures

◮ most likely: thermal BB emission from central parts of AGN (Torus, gas, dust)

◮ temperatures for dust:≈20−80 K

◮ no polarization→thermal emission!

◮ Planck’s law:

B_ν(T) = 8πhν³ c³e^kThν−1

(14)

0[13]

IR - UV (thermal black body radiation)

IR Bump

◮ near≈10¹³keV

◮ thermal emission of warm dust (T >

2000 K) near black hole

UV Bump

◮ in general: strong, broad line emission from BLR/NRL→ continuum more difficult to model than in IR!

◮ Big Blue Bump (BBB) from hot accretion disc or free-free emission (bremsstrahlung)

◮ thermal BB emission of the temperature-profile

0[13], [7], [15]

Compton scattering:energy transfer photon→electron

inverse Compton scattering:energy transfer electron→photon

λ^′−λ= h

mec^{(1−cosθ) (15)}

E_e^′= E 1+_m^E

ec²(1−cosθ) (16)

∆E E ^{≈ −}

E

mec^{2 (}E≪mec²) (17) From Eq.16 for many scattering events (cf. Eq.11):

I=dE dt ⁼

4

3σTcγ²Uel (18)

0[13], [7], [18]

relativistic boosting

Time dilatation causes relativistic Doppler effect with νobs= νem

γ(1−βcosθ) (19)

with the relativistic Doppler factor D=

p1−β²

(1−βcosθ) (20)

One can show, that ^Iobsν

ν³_obs =_ν^Iemν3 em

⇒ I_ν^obs=D³I_ν^em power lawI_ν∼Aν^α ⇒ I^obs_ν =D^3−αI_ν^em

π+θπ

I1

I2 = 1+βcosθ 1−βcosθ

!3−α

(21)

In addition: relativistic abberation

Superluminal Motion

apparent speed of a blob:

vapp= vsinθ

1−βcosθ (22)

“superluminal” only for relativistic blob- speeds (largeβ) at small viewing angles Φ

0[18], [13]

VLBA monitoring at 2cm

0[6]

tracking flares of 3C111

radio lightcurve(top figure)

◮ blob first visible at high frequencies (synchrotron self absorption mainly at lower frequencies)

◮ blob expands⇒less dense electron plasma⇒less synchrotron self absorption spectral indices(bottom figure)

◮ spectral indicesαfromI_ν∼ν^α

◮ compact blobs in plateau-state⇒ flat radio spectrum (α≈0)

◮ decay state: blob expands⇒radio spectrum steepened (α <0)

0[6], [16], [8]

relationship radio - gamma([17])

◮ comparisonradio(22 GHz and 37 GHz, Metsähovi Obs.) -gamma(EGRET)

◮ radioemission several monthafter gammaemission

◮ coupling gamma - radio: both originate in same flare↔gamma rays from SSC-upscattering of synchrotron seed photons (from accelerated relativistic electrons)

relationship optical - radio([16]: Generalized Shock Model)

◮ connection: accreted matter (→optical thermal emission) - radio-flare

◮ strong delay between accretion and radio-flare expected

◮ or: optically thin slope of synchrotron spectrum reaches optical waveband→no delay!

0[16], [17], [9]

UMRAO Radio Observatory

00.511.5Fν [W/m2Hz]

Historic Lightcurve PKS 2155−304

00.511.5Fν [W/m2Hz]

46000 48000 50000 52000 54000

00.511.5Fν [W/m2Hz]

MJD 4.8 GHz (UMRAO)

8 GHz (UMRAO)

14.5 GHz (UMRAO)

Effelsberg Radio Telescope

0.51

Historic Lightcurve PKS 2155−304

0.510.510.51Fν [W/m2Hz] 0.51

14400 14600 14800 15000

0.51

MJD (JD − 2400000)

13mm

20mm

28mm

36mm

60mm

110mm

Effelsberg lightcurves of PKS 2155-304

2 4 6 8 10 12 14 16

0.40.60.811.21.4

F_ν Spectrum of PKS 2155−304

ν [GHz]

Fν [W/m2Hz]

MJD = 15072 MJD = 14359

simultanious observation of the flare with HESS (gamma), Chandra (X-ray), RossiXTE (X-ray), Bronberg Obs. (optical)

SED of PKS 2155-304 with highest and lowest states during this observa- tion

◮ first peak, right slope: X-Ray (Synchrotron emission)

◮ second peak: Gamma (inverse Compton emission)

◮ flare not moving though frequencies with time

Why X-Ray through Synchrotron emis- sion??

◮ “blue blazars”

→less external photons→less Compton cooling of electrons→ overall higher photon energies due to synchrotron or inverse Compton recoil

◮ “red blazars”

→higher photon density→lower photon energies

0[1], HESS-collaboration (2009)

Multiwavelength observations of the 2006 flare of PKS 2155-304

plot of spectral index’ and flux variability

◮ strong correlation between X-ray andγ-ray flux (synchrotron and inverse Compton emission→as already shown)

◮ γ-ray flux decreases approximately with cube of X-ray flux (F_γ∼F_X³)

0HESS-collaboration (2009)

[1] J.M. Bay et al. Existence of large-scale synchrotron x-ray jets in radio-loud active galactic nuclei. paper, 2001.

[2] Francis Burke, Bernard F.; Graham-Smith. An Introduction to Radio Astronomy. Cambridge University Press, Cambridge, United Kingdom, 2009.

[3] D. Donato et al. Hard x-ray properties of blazars. paper, 2001.

[4] B. Garcia-Lorenzo et al. Spectroscopic atlas of the central region of the seyfert 2 galaxy ngc 1068. paper, Instituto de Astrofisica de Canarias, 1999.

[5] K.D. Gordon et al. Spitzer/mips infrared imaging of m31: Further evidence for a spiral/ring composite structure. paper, 2006.

[6] M. Kadler et al. The trails of superluminal jet components in 3c 111. paper, 2007.

[7] Narlika Jayant V. Kembhavi, Ajit K.Quasars and Active Galactic Nuclei. Cambridge University Press, Cambridge, United Kingdom, 1999.

[8] Alan P. Marscher et al. Models for high-frequency radio outbursts in extragalactic sources, with application to the early 1983 millimeter-to-infrared flare of 3c 273.

paper, 1985.

[9] Alan P. Marscher et al. Observational evidence for the accretion-disc origin for a radio jet in active galaxies. paper, 2002.

[10] Thanu Padmanabhan.Theoretical Astrophysics, Volume 3, Galaxies and Comoslogy. Cambridge University Press, Cambridge, United Kingdom, 2002.

[11] Oleg Pankratov. Theoretische physik, elektrodynamik, 2008. Lecture WT 2008/2009 University Erlangen-Nürnberg.

[12] Drechsel Przybilla. Sternatmosphären und strahlungsphänomene, 2009. Lecture WT 2009/2010 University Erlangen-Nürnberg.

[13] Ian Robson.Active Galactic Nuclei. Wiley, Chichester, England, 1996.

[14] G. B. Rybicki.Radiative Processes in Astrophysics. Wiley-Vch, Weinheim, 2004.

[15] Peter Schneider.Einführung in die Extragalaktische Astronomie und Kosmologie. Springer, Berlin, Germany, 2007.

[16] E. Valtaoja et al. Five years monitoring of extragalactic radio sources - iii.

generalized shock models and the dependence of variability on frequency. paper, 1992.

[17] E. Valtaoja et al. The relationship between gamma emission and radio flares.

paper, 1996.

[18] Kadler Wilms. Active galactic nuclei, 2010. Lecture ST 2010 University Erlangen-Nürnberg.