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Nonthermal radiative processes

Nonthermal radiative processes

This lecture is part of the course "physics of active galactic nuclei" offered to graduate students in astrophysics by Rodrigo Nemmen and Joao Steiner at IAG USP.

https://rodrigonemmen.com/teaching/active-galactic-nuclei/

Rodrigo Nemmen

May 20, 2016
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  1. Rodrigo Nemmen
    Non thermal Radiative
    Processes
    AGA5727 - Active Galactic Nuclei
    Credit: ESO

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  2. Ghisellini
    Black body intensity compared to Raleigh-Jeans
    and Wien laws 2 Bremsstrahlung and Black Body

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  3. Main applications of blackbodies to AGNs
    Dusty torus
    . 1 pc
    Accretion disks
    10 5 pc . l . 0.1 pc
    T~100 K
    T~104-105 K

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  4. Synchrotron radiation: Single electron in a
    uniform magnetic field

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  5. Synchrotron radiation: Single electron in a
    uniform magnetic field

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  6. Synchrotron spectrum of single electron in a
    uniform magnetic field
    m Emitted by the Single Electron 53
    panel: The
    /νc) describing
    on spectrum
    e single electron.
    : F(ν/νc) is
    h some
    g formulae, as
    ave defined
    Ghisellini

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  7. Extended radio lobes in AGNs
    Hercules A

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  8. Radio jets
    M87

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  9. Synchrotron spectrum of self-absorbed source
    Beckmann
    2.2 Synchrotron Emission 31
    optically thick
    optically thin
    0
    1
    1
    1
    .
    0
    0.1
    1

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  10. Synchrotron spectrum of self-absorbed source in
    log space and physical units
    Ghisellini
    sorption: Electrons 59
    tron
    ally
    ld
    tions of
    electron

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  11. Synchrotron spectrum of self-absorbed source
    vs blackbody
    Netzer
    Nonthermal radiation processes
    1013 1014 1015 1016 1017
    .0001
    .001
    .01
    .1
    1
    10
    frequency
    normalized L
    ν
    T=105 K
    ν5/2 ν2
    Figure 2.1. A comparison of a synchrotron source with p = 2.5 (solid line) and a
    5

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  12. Polarization of synchrotron sources
    Blandford
    f Linear
    B Polarisation
    Fig. 2.3. a) Polarisation of cyClotron radiation from a non-relativistic electron. b) Polarisa-
    tion of synchrotron radiation from a relativistic electron.
    usually polarised to a degree that ranges from '" a few per cent to '" 60 per
    cent. Partly for this reason, it is thought to be synchrotron radiation.
    2.2.3 Emission by a power-law electron distribution function. The electrons in

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  13. Polarization of synchrotron sources
    Blandford
    f Linear
    B Polarisation
    Fig. 2.3. a) Polarisation of cyClotron radiation from a non-relativistic electron. b) Polarisa-
    tion of synchrotron radiation from a relativistic electron.
    usually polarised to a degree that ranges from '" a few per cent to '" 60 per
    cent. Partly for this reason, it is thought to be synchrotron radiation.
    2.2.3 Emission by a power-law electron distribution function. The electrons in

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  14. Some sites of synchrotron radiation in AGNs
    Blandford
    radiation is 100 per cent circular polarised. Now let the electron move with a
    relativistic speed and beam this radiation in the direction of motion. The two
    components of circular polarisation will effectively cancel, whereas the linear
    polarisation will largely survive. The net effect is a typical degree of polarisa-
    tion of '" 70 per cent. The radio emission from extragalactic radio sources is
    Table (2.1). Possible synchrotron radiation sites and characteristic physical parameters.
    Location B 1/
    ,
    tcool tdyn Pmin Umin
    G Hz yr yr dyne cm-2 erg
    Extended Radio Source 10-5 109 104 107 108 10-11 1059
    Radio Jet 10-3 109 103 104 104 10-7 1057
    Compact Radio Source 10-1 109 102 10 10 10-3 1054
    Outer Accretion Disk 10 1014 103.5 10-4 1 10 1049
    Inner Accretion Disk 103 1016 103.5 10-8 1 105 1047
    Black Hole Magnetosphere 104 1018 104 10-10 10-3 107 1047
    169

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  15. Fig. 8.—Same as Fig. 1, but for 3C 272.1 (LX = 6.8 ; 10À8LEdd). The emis-
    Edd). The total
    WU, YUAN, & CAO Vol. 669
    Wu et al. 2007, ApJ
    Applications of synchrotron to AGNs: radio
    galaxy spectral energy distributions

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  16. Thin disk model
    Nemmen & Brotherton (2010)
    Radio-loud
    Radio-quiet
    Quasar spectral energy distributions
    log (radiation flux)
    log (frequency / Hz)
    Shang, …, Nemmen et al. (2011)

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  17. Second Series May, lying Vol. zI, Po. 5
    THE
    P HYSICA: REVIEW
    A QUANTUM THEORY OF THE SCATTERING OF X—
    RAYS
    BY LIGHT ELEMENTS
    BY ARTHUR H. CoMPToN
    ABSTRACT
    A quantum theory of the scattering of X-rays and p-rays by light elements.

    The hypothesis is suggested that when an X-ray quantum is scattered it
    spends all of its energy and momentum upon some particular electron. This
    electron in turn scatters the ray in some definite direction. The change in
    momentum of the X-ray quantum due to the change in its direction of propaga-
    tion results in a recoil of the scattering electron. The energy in the scattered
    quantum is thus less than the energy in the primary quantum by the kinetic
    energy of recoil of the scattering electron. The correspondingincrease in the
    wave-length of the scattered beam is Xg

    Xp
    = (2h/mc) sin'-,'9 = o.o484 sin'-', 8,
    where h is the Planck constant, m is the mass of the scattering electron, c is
    1927

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  18. Squaring these equations, we obtain
    (po — pi cos 0)2 =p2 cos2 (p
    and
    pi sin2 B = p2 sin2 cp
    Photon
    E0,P0
    V ^
    X
    Electron
    K,p
    Before After
    Figure 2-7 Compton's interpretation. A photon of wavelength 2 is incident o
    electron at rest. On collision, the photon is scattered at an angle B with increas
    length 2', while the electron moves o ff at angle 'p.

    ⌫0
    Eisberg & Resnick
    Compton scattering

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  19. hot electrons
    photon source
    Inverse Compton scattering

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  20. S⌫

    ⌫ ↵
    ⌫0
    hot electrons
    photon source
    Inverse Compton scattering

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  21. S⌫

    ⌫ ↵
    ⌫0
    hot electrons
    photon source
    Inverse Compton scattering

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  22. Blandford
    Spectrum of monochromatic source embedded
    within a hot electron scattering region
    Fig. 2.6. Spectrum produced by a monochromatic pho
    ded within a hot electron scattering region. The slope
    Comptonisation parameter y, given by equation(2.38}.
    acceleration rate to the escape rate. The spectrum e
    ⌫0

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  23. Blandford
    Synchrotron self-Compton spectrum: synchrotron
    photons are inverse Compton scattered by rel. electrons
    are related by equation(2.15)and the limits of integration are exhib-
    cally in Fig.(2.8). The spectral index of the synchrotron radiation is
    ely preserved in the inverse Compton emission.
    Synchrotron
    I V-a(
    £I 6max2c.> G
    lJ' d"max2 WG
    i 2if _ 2fT 2TT))
    Limits of integration for equation(2.42). The electron distribution function is
    xtend as a power law from "Ymin to "Ymax. Combinations of synchrotron pho-
    and electron energy radiating a given Compton frequency are shown. b) The
    ctrum extends as a rough power law (ignoring weakly-varying logarithmic fac-
    "Y!.inwa/21r to '" "Y:"axwa/21r.
    synchrotron
    IC

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  24. Application of pair production: Fermi Gamma
    Ray Telescope, 20 MeV - 300 GeV
    Fermi 2-year all sky

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  25. Bremsstrahlung radiation is emitted when
    electrons collide with ions or positrons

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  26. 2 Bremsstrahlung and Black Body
    ung
    ity
    y for
    of
    n if
    is
    ung Ghisellini
    Bremsstrahlung intensity for a spherical source
    with different temperatures
    R = 1015 cm
    ne = np = 1010 cm 3

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