Applications Of Synchrotron: Radio Sources & AGN Flashcards
Summarise the radio source features.
Matter accretes onto a black hole at the heart of a host galaxy. Radio Jets arise from the central core, 10s-100s kpc, much bigger than size of the optical host galaxy. Jets end in bright hotspots, where jet material is shocked and then spills out into extended lobes of synchrotron emission. The lobe emission only observed at radio wavelengths, but synchrotron emission from core, jets and hotspots can be seen at higher energies. A bow shock associated with the expanding radio source shocks the IGM, shocked IGM typically remains separated from the relativistic synchrotron plasma through a contact discontinuity
For a source moving from A to B at velocity v and an angle θ between the line of sight and the direction of travel, what is the difference in arrival time?
Δt = (ct - vtcosθ)/c
What is the Doppler factor?
D = 1/γ(1-βcosθ)
The change in energy/frequency of an emitting blob of radiation between S’ and S frames
How does the flux received at freq ν from a blob moving at angle θ to the line of sight relate to the emitted flux at freq ν’?
S_(rec, ν) = (D^3)S_(emit, ν’)
What are the main uncertainties in the estimate for jet energy of a radio source using energetically from a synchrotron?
Kappa (accounts for energy in relativistic particles eg protons that don’t contribute to the observed radiation). Jet composition thought to be mostly electron-positron but there are indications of proton involvement.
νbar^-(1/2) encapsulates effects of parameters which could be determined from the radio spectrum (low and high energy cutoffs, slope of electron energy distribution). Low energy cutoff has not been well-quantified by observations
Other uncertainties: magnetic field strength, filling factor of the lobes
Describe how to calculate energetic from inflated cavities.
Examine Bremsstrahlung emission of hot gases into which the radio source is expanding. RS observed to inflate cavities in hot X-Ray gas, associated with expanding bow-shock of the RS. From ideal gas internal energy density U=3P, E_rel = 3PV. Energy to inflate cavity is PV. Therefore E_tot = 4PV
Why is the considerable scatter on relationship between jet power and radio luminosity expected?
For fixed jet power, radio luminosity of a source is known to evolve significantly over its lifetime
Describe the lifetime of a radio source.
Initially luminosity increases with time due to Gigahertz-Peaked-Spectrum (/compact steep-spectrum) sources. Then the RS reaches a stage where the injection of new relativistic electrons is balanced by losses in the existing population, the luminosity will then flatten. It will fall slowly with time until eventually the radio jet switches off and remaining relativistic plasma will fade.
Describe where the injection of energy by RS is most prevalent.
Where cooking rates are highest and the energy injected into the cluster will be at the required level to balance cooling losses with cooling radius
What happens in a RS if the AGN is switched off and then back on.
When off, the radiatively cooling losses are not offset, the cooling rate then increases and the fuel supply for AGN is increased.
When turned back on, AGN is too powerful and the heating rate exceeds cooling. The gas is heated and expanded, the gas supply to AGN is decreased and the heating rate is decreased.
What is the most luminous example of an AGN?
Quasar
What is the Schwarzchild radius?
R_S=2GM_{BH}/c^2
What is the dominant energy source for quasars and in what waveband does it peak?
Thermal Blackbody emission which peaks in the optical/UV waveband
What are Type 1 and Type 2 AGN?
Type 1 can be directly viewed.
Type 2 are obscured from view by the obscuring torus
Describe how the host of a Radio Source changes depending on where you observe it and what this phenomena is called.
From direction close to torus axis: quasar
From close to skyplane: radio galaxy
Orientation based unification scheme
