Radio emission from active

galactic nuclei

Anne Lähteenmäki

Aalto University Metsähovi Radio Observatory

& Dept of Radio Science and Engineering

Today

Active galactic nuclei (AGN)

Radio emission from AGN & jet models

Radio spectra and spectral energy distributions (SEDs)

Examples:

• Single-dish radio data

• Multifrequency data

R&O PKS2356-61

Active Galactic Nuclei (AGN)

Active Galactic Nuclei (AGN)

AGN classification

Radio-loud

• 15% of all AGN

• Powerful radio jets

Radio-quiet

• IR, optical, UV

• No/weak radio jets and/or star formation processes

Ron K

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aard

Outdated!

Ideally… but not necessary in real life…

At radio frequencies we see

synchrotron emission

Variable jet and radio core

Non-variable radio lobes and hot spots

FR II

AGN @radio

Relativistic beaming

Superluminal motion

Doppler boosting factor

Lorentz factor

Viewing angle

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Shocked jet model Marscher & Gear 1985

http://www.bu.edu/blazars/

Turbulent extreme multi-zone model (TEMZ) Marscher 2014

http://www.bu.edu/blazars/

Multifrequency observations of AGN

TeV

X-rays Gamma-rays

Optical Radio

Spectral energy distributions (SEDs) of AGN

Sambruna 1994

Synchrotron component

Inverse Compton (IC) component:

External Compton (EC) or Synchrotron Self-Compton (SSC)

Radio spectra of AGN

Typically flat radio spectra due to overlapping shock components

”Evolving shocks”

Radio spectra and SEDs…

Properties of the AGN and the host galaxy

Emission mechanisms

Turnover frequency

• Turnover flux density

• Size, magnetic field strength

Energy requirements

SED modelling

Contemporary models fit the high-energy IC part rather nicely, but (still) almost completely ignore the synchrotron part which most likely is the source for the high-energy emission.

Bonnoli et al. 2010

Multicomponent SED modelling

Start with the underlying physics and fit the primary photons (i.e. synchrotron, also at low frequencies!) first.

Use multicomponent fitting:

• underlying jet flow + individual shocks moving in the jet.

3C 454.3 Tammi et al.

Examples

Case 1: Total flux density variations in AGN

Case 2: SEDs and radio spectra of AGN using Planck satellite data

Case 3: Multifrequency correlations

Case 1: Total flux density variations in AGN

Metsähovi

UMRAO

Flare characteristics: fitting the lightcurve

Decay timescale is 1.3 times the rise timescale.

Jet parameters Observed variability timescale

Maximum flare amplitude Smax

Apparent superluminal speed app (from VLBI)

Brightness temperature:

Doppler factor:

Lorentz factor:

Viewing angle:

Lähteenmäki & Valtaoja 1999

Variability analysis

How much, how often: long term variability timescales

Various methods (structure function, periodogram, DCF, …)

4C 29.45, Hovatta et al. 2007

• Average long term timescales ~7 years

• Different timescales for source types • Sources are mostly in a quiescent or intermediate state, big flares happen fairly rarely.

Case 2: SEDs and radio spectra of AGN using

Planck satellite data

14.5.2009 – 23.10.2013

Cosmic microwave background (CMB) + foreground sources

9 frequencies 30 – 857 GHz

5 to 8 full sky surveys

Simultaneous multifrequency data: one epoch Planck Collaboration 2011

104 sources

Planck, 9 frequencies (30 – 857 GHz)

Radio (1 – 345 GHz)

• Metsähovi, RATAN-600, UMRAO, VLA, ATCA, Effelsberg, IRAM, APEX, OVRO, Medicina

Optical

• Tuorla + KVA (La Palma), Xinglong

X-rays (+optical+UV)

• Swift

Gamma-rays

• Fermi

3C 454.3

OJ 287

Case 3: Multifrequency correlations

Metsähovi 37 GHz & Fermi gamma-ray data

Summary

Active galactic nuclei (AGN)

Radio emission from AGN & jet models

Radio spectra and spectral energy distributions (SEDs)

Examples:

• Single-dish radio variability data

• Multifrequency data: SEDs and correlations