Compton Efficiencies; Fermi and the sequence
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Compton Efficiencies; Fermi and the sequence

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Compton Efficiencies; Fermi and the sequence




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Presentation on theme: "Compton Efficiencies; Fermi and the sequence"— Presentation transcript:

Slide1

Compton Efficiencies; Fermi and the sequence

Can we see statistical evidence for the influence of external (AGN) photons in

blazar

SEDs?

(Jenny Gupta, Mike Peel)

Slide2

Blazar SEDs

Have Characteristic twin peaks

Synchrotron dominating radio through optical

Inverse Compton dominating hard X-rays and gamma-rays

Major question:

Are the photons that get Compton scattered those internally generated (synchrotron self-Compton) or external ones from the AGN?

Secondary question:

Is there a progressive sequence of

blazar

SED properties that depends on the availability of external photons? (

Blazar

sequence

)

Slide3

Slide4

Compton Efficiencies

Blazars

dominate the Fermi sky – i.e. objects selected by their Compton scattered emission

Consider the Fermi

blazar

catalogue

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

Expect those

blazars

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

Lacs

only have their synchrotron photons

Predict:

FSRQs would have higher Compton efficiencies than BL

Lacs

Within the FSRQ population itself one might expect a trend with AGN luminosity

Slide6

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 densities

Slide7

CRATES objects with OCRA measurements

Slide8

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

Abdo

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 <~100mas

Slide9

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

ν

S(

ν

) 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

ν

S(

ν

) at 8.4GHz (no k-correction done)

Slide10

Specrtal

energy plot.

BLLacs

+

and FSRQs X

Slide11

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 level

Slide12

Nasty details!

Finding the peak

ν

S(

ν

). Not all the objects in the sample have the peak in the Fermi band.

Abdo

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

ν

S(

ν

) not S(

ν

).

Slide13

What does is all mean?

The availability of external photons does not affect the Compton efficiency.

FSRQs have lots

BL

Lacs

have very few

This is another reason to be sceptical about any “

blazar

sequence” idea that attempts to unify BL

Lacs

and FSRQs.

Slide14

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?

No!

Slide15

Compton efficiencies for objects with Veron&Veron absolute magnitudes

Slide16

Compton efficiencies in FSRQs

There is no dependence on optical luminosity

Why?

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 component

Slide18

Today’s new Sequence

The SSC component is the same in BL

Lacs

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

Lacs

It accounts for the broader range of Compton efficiencies for FSRQs

Slide19

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 level

Slide20

Slide21