Can we see statistical evidence for the influence of external (AGN) photons in . blazar. SEDs?. (Jenny Gupta, Mike Peel). Blazar. SEDs. Have Characteristic twin peaks. Synchrotron dominating radio through optical. ID: 272760
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Compton Efficiencies; Fermi and the sequence
Can we see statistical evidence for the influence of external (AGN) photons in
(Jenny Gupta, Mike Peel)Slide2
Have Characteristic twin peaks
Synchrotron dominating radio through optical
Inverse Compton dominating hard X-rays and gamma-rays
Are the photons that get Compton scattered those internally generated (synchrotron self-Compton) or external ones from the AGN?
Is there a progressive sequence of
SED properties that depends on the availability of external photons? (
dominate the Fermi sky – i.e. objects selected by their Compton scattered emission
Consider the Fermi
Start with the premise that radio core emission is a good proxy for the energy available in ultra-relativistic electrons that can scatter photons to produce gamma rays.
This implies that those Fermi sources with the weakest radio cores have the highest “Compton efficiencies”Slide5
External photons and Compton efficiencies
with a higher energy density in low frequency photons to have higher Compton efficiencies
FSRQs have lots of AGN photons (directly from the accretion disk and reprocessed by dust) while BL
only have their synchrotron photons
FSRQs would have higher Compton efficiencies than BL
Within the FSRQ population itself one might expect a trend with AGN luminositySlide6
A quick look
Plot of Gamma ray flux (1 – 100GeV) against 8.4 GHz flux densityObjects from Fermi First year catalogue (Abdo et al ???) and identified with CRATES radio sourcesBL Lacs red +FSRQs green XBL Lacs have lower radio flux densitiesSlide7
CRATES objects with OCRA measurementsSlide8
The sample: Fermi Blazars with CRATES identifications
We want a gamma ray-selected sample with radio identifications and with information on the compact radio emission.
CRATES is a suitable sample and has the advantage that
et al. list CRATES sources which match detections in their first year sample.
Gamma ray fluxes plus photon indices
Radio flux densities at 8.4GHz of cores <~100masSlide9
Measuring Compton efficiencies
Don’t take previous plot too seriously!
A proper definition of efficiency would be in terms of energies or luminosities, not flux densities.
As a measure of the gamma ray luminosity we take the peak
) in the SED. This takes care of the fact that BL Lac and FSTQ SEDs peak at different energies
For a measure of the jet power we take
) at 8.4GHz (no k-correction done)Slide10
and FSRQs XSlide11
Compton efficiency distributions
The Peak Compton efficiencies for BL Lacs and FSRQs are not significantly different but, anything the FSRQs are less efficient.The FSRQ distribution is broader at the 2.5% significance levelSlide12
Finding the peak
). Not all the objects in the sample have the peak in the Fermi band.
et al. give a recipe to find the peak frequency in the SED using the photon index
Fit a parabola to the Fermi points using the recipe to fix the peak. (Additional assumptions required in a few cases.)
Less than 50% of the gamma ray sources have identified radio counterparts.
Hope that resulting selection effects are the same for all the sample so should not change the conclusions based on comparisons within the sample
Variability blurs any effect (8.4GHz flux densities measures in 1990s
Would really like to select sample in
) not S(
What does is all mean?
The availability of external photons does not affect the Compton efficiency.
FSRQs have lots
have very few
This is another reason to be sceptical about any “
sequence” idea that attempts to unify BL
Evidence for the effects of external photons within FSRQs?
Detailed SED modelling (e.g. 3C454.3) requires external Compton to get a fit.
Can we see statistical evidence using Compton efficiencies?
Look for a correlation within the FSRQ population
Do more optically luminous quasars have higher efficiencies?
Compton efficiencies for objects with Veron&Veron absolute magnitudesSlide16
Compton efficiencies in FSRQs
There is no dependence on optical luminosity
It’s really energy density in photons within the jet that’s relevant
Some of the optical luminosity is beamed. (Emission line luminosity is better parameter)
Conclusion; it would have been nice to see a correlation but we don’t.Slide17
The Sequence is dead, long live the Sequence!
External photons are a fact of life; we need them to explain detailed SEDs
The mistake is to believe that they have an energetically dominant effect. Compton efficiency argument say that they do not
The SED fitting indicate that the integrated gamma luminosities in the external Compton component is sub-dominant.
Importantly it usually contributes a lower energy gamma componentSlide18
Today’s new Sequence
The SSC component is the same in BL
and FSRQs. (Jet production cares little about the optical AGN.)
Scattering of external photons produces a sub-dominant gamma component at lower energies than the SSC component
This component drags the SED peak to lower energies in FSRQs than in BL
It accounts for the broader range of Compton efficiencies for FSRQsSlide19
Compton efficiency distributions
The Peak Compton efficiencies for BL Lacs and FSRQs are not significantly different but, anything the FSRQs are less efficient.The FSRQ distribution is broader at the 2.5% significance levelSlide20Slide21