radio emission from active galactic nuclei - turun yliopisto · pdf fileagn classification...
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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
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
ollg
aard
At radio frequencies we see
synchrotron emission
Variable jet and radio core
Non-variable radio lobes and hot spots
FR II
Relativistic beaming
Superluminal motion
Doppler boosting factor
Lorentz factor
Viewing angle
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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
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