Synchrotron Single particle spectrum Ghisellini Fig. 4.4 Top panel - - PowerPoint PPT Presentation

Synchrotron

• A. Marconi

Relativistic Astrophysics 2016/2017

Single particle spectrum

2

• Fig. 4.4 Top panel: The

function F(ν/νc) describing the synchrotron spectrum emitted by the single electron. Bottom panel: F(ν/νc) is compared with some approximating formulae, as

• labeled. We have defined

x ≡ ν/νc

Ghisellini

From Cyclotron to Synchrotron

• Fig. 4.5 From cyclo to synchro: If the emitting particle has a very small velocity, the observer sees

a sinusoidal (in time) electric field E(t). Increasing the velocity the pattern becomes asymmetric, and the second harmonic appears. For 0 < β ≪ 1 the power in the second harmonic is a factor β2 less than the power in the first. For relativistic particles, the pattern becomes strongly beamed, the emission is concentrated in the time tA. As a consequence the Fourier transformation of E(t) must contain many harmonics, and the power is concentrated in the harmonics of frequen- cies ν ∼ 1/tA. Broadening of the harmonics due to several effects ensures that the spectrum in this case becomes continuous. Note that the fundamental harmonic becomes smaller increasing γ (since νB ∝ 1/γ )

Ghisellini

• A. Marconi

Relativistic Astrophysics 2016/2017

Spectrum of a self-absorbed source

4

• Fig. 4.6 The synchrotron

spectrum from a partially self-absorbed source. Observations of the self-absorbed part could determine B. Observations of the thin part can then determine K and the electron slope p

Ghisellini

• A. Marconi

Relativistic Astrophysics 2016/2017

The Radio emission of the Milky Way

5

Map of Milky Way in the visible

• A. Marconi

Relativistic Astrophysics 2016/2017

The Radio emission of the Milky Way

6

Map of Milky Way in the radio at 408 MHz

• A. Marconi

Relativistic Astrophysics 2016/2017

The Crab Nebula

7

• Fig. 5.10 Images of the Crab nebula at different wavelengths. Left upper: radio image from the

NRAO; right upper: infrared image at 2 µ from 2MASS; left lower: optical image from VLT/ESO; right lower: high-resolution X-ray image from Chandra

• A. Marconi

Relativistic Astrophysics 2016/2017

The Crab Nebula

8

Sync. Dust Diffused Star Light Sync. Inverse
 Compton

• A. Marconi

Relativistic Astrophysics 2016/2017

Active Galactic Nuclei (AGN)

9

galaxy:
 stars only → Introduzione all’Astrofisica

The AGN Unified Model

• A. Marconi

Relativistic Astrophysics 2016/2017

Active Galactic Nuclei (AGN)

11

• A. Marconi

Relativistic Astrophysics 2016/2017

Radio Galaxies

12

Jet asymmetry 
 = relativistic beaming

3C 273

103 10–3 10–6 10–9 10–12 10–9 10–10 10–11 10–12 10–13 109 1012 1015 Frequency [Hz]

b a

1018 1021 1024

1

1 meV 1 meV 1 eV 1 keV Photon energy Flux density Fν [JY] νFν [erg/cm2/s] 1 MeV 1 GeV

Synchrotron Hot dust Accretion disk X ray corona

M87

M87

Cygnus A

1 2 3 4 5 6 7 8 9 10 11 12 13 L Central Source Radio Lobes Cygnus A Log Sν (Jy) −3 −6 −2 −1 −4 −5 1 2 3 4 5 Log n (MHz)

• Fig. 20.12

Radio to optical spectrum of Cygnus A (Hobbs et al. 1978, Fig. 1 p. L79, reproduced by permission of the AAS). The radio lobe spectrum shows a turnover near 20 MHz, then follows a power law with index −0.8 up to 1 GHz and −1.2 up to 100 GHz. The radio data of the central source are consistent with a rising spectrum (index 1/3), although a flat spectrum is not excluded

Courvoisier 5.0 GHz 170 kpc

Cygnus A

Radio - Synchrotron X Rays - Bremsstrahlung