Very High Energy Gamma-Raysfrom Flat Spectrum Radio
Quasars!

Elina Lindfors,ICRR Tokyo and Tuorla Observatory, University of Turku, Finland
Collaborators: J.Sitarek, J. Becerra Gonzalez, F.Tavecchio et al.
MWL Collaborators: S. Jorstad, T. Hovatta, A. Lähteenmäki, M. Tornikoski, S.Buson,
F. D’Ammando, V. Fallah Ramazani, C. Raiteri...and many more....

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Gamma-ray sky

Blazars!

The most
numerous objects
in the gamma-raysky2Extragalactic VHE sky
More than 60 sources
Dominated by blazars!

3Blazars - hosting relativistic jets

4Blazar model
BL Lacs: no accretion disk, no Broad Line Region, no IR Torus
FSRQs: accretion disk, Broad Line Region Clouds, IR torus!

(e.g. Giommi, Padovani et al. 2012)

5Figure: Alan Marscher

Flat Spectrum Radio Quasars!
●

The most luminous sources within gamma-ray emitting AGN class●Multiwavelength characteristics:-the VLBA jets with high Doppler factors, “knots” in the jet-optical spectrum shows broad emission lines-SED: low synchrotron peak frequencies (infrared)●In VHE (>100GeV) gamma-rays 7(?) known:
3C279, PKS1510-089, PKS1222+216-PKS1441+25 and B0218+357 the newbies-S4 0954+65 and BL Lac disputed classifications●In Fermi >10GeV catalog 70 FSRQs
2Emission mechanism?
Leptonic: synchrotron + inverse Compton scattering
Hadronic: photo-pair and photo- pion production, the cascades initiated by
γ γ absorption of ultrahigh energy (UHE; E ≫ 1 TeV) photons produced throughπ0 decay and synchrotron emission of pions and their decay products.

!

Both can fit the SEDs, but: “The hadronic model presented here has difficulty describing the GeV break in theSEDs of two FSRQs, but provides appropriate fits for all other blazars in our sample.
However, the fits require very large powers in relativistic protons, of LP ∼ 1047 –1049 erg s−1 ,in most cases dominating the total power in the jet.

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Leptonic

Hadronic(Bottcher et al. 2013)

Emission scenarios:“Close to the central engine”
l Emission region close tocentral engine is the mosteconomic way to produce thehigh luminosity (e.g. work by G.
Ghisellini)l And the most natural way toaccommodate the short timescale variability (e.g. Tavecchio et al.
2010, MNRAS,405,94)l A strong depression above ~20
GeV due to absorption (Donea &Image credit: Tavecchio & Ghisellini 2012

Protheroe 2003; Sitarek & Bednarek 2008;
Tavecchio & Mazin 2009; Poutanen &Stern 2010). Scenario excluded if VHE
emission observed (e.g. Tavecchio&3Ghisellini 2012), however ongoing debate(e.g. Stern & Poutanen 2014)

Emission scenarios:“Far out emission region”●●●Coincident timing of the radio (mmflares, ejection of new components
from VLBA core) and gamma events:
Main part of the emission originates
close to the 43GHz VLBA core(suggested already in EGRET era by
Valtaoja et al. 1996, Jorstad et al.
2001)
What is the source of the seedphotons for the IC scattering (aninfrared torus, a sheath, a standingshock?)

Image credit: Marscher et al. (2010): Moving emission feature on helicalpath, hits the conical standing shock=> gamma-ray flare, ejection of
new component from the VLBA core

What mechanism produces the fast
gamma-ray variability (mini-jets?
Magnetic reconnection? Turbulencecaused by recollimation?)
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Image credit: Giannios (2012): Re-connection driven plasmoids

What can we learn by observing
VHE emission?
Absorption: very severe, if theemission region inside BLR

Rapid variability: very smallemission region!

=> If we see VHE, the emission region=>Very challenging to produce
is outside BLRsuch emission region

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Bottcher et al. 2016

Aleksic et al. (MAGIC Collaboration), 2011

What can we learn from opticalpolarisation?
Rotations of EVPA seen in many sources( BL Lac, PKS 1510-089, 3C279…)•-Geometrical effect (bend in the jet?)•-Emission feature moving along the•streamline in acceleration and•collimation region?

Marscher et al. 201011

What can we learn from radio
observations?
• Synchrotron self absorption; radio emission
cannot originate very close to the central
engine (~5-15pc from central engine)• Flares in radio, ejection of knots in VLBA =>emission region far from the central engine

Marscher et al. 2012
Leon-Tavares et al. 2011

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PKS 1510-089 in 2012●●●●

MAGIC observations were
triggered by the high state in
HE gamma-ray band
Simultaneous variability at37GHz and HE gamma-rays
Rotation of the opticalpolarization angle >180
degreesEjection of new VLBA
component

8!

Aleksic et al (the MAGIC Collaboration). 2014, A&A

Far-out emission region SED modelling
Energy density of the photon field as function of the distance from the central engine

Blue: BLR
Red: IR torus
Aleksic et al. 2014, A&A!
!
!

Seed photons from torus!
!

Seed photons from slow sheath

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Ghisellini et al. 2005, observational evidence for
PKS1510-089 in MacDonald, Marscher et al. 2015

Far out SED modelling:
PKS 1510-089 in 2012l Spectral energy distribution (average!) assuming seedphotons for External Compton model from far out resources IR
torus OR from slow sheath of the jet!
!
!
!
!
!
l

Far out scenario works here, does it work in general?

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PKS 1510-089
story continues• Data from 2009-2015• Radio-optical polarizationgamma connected?
!
!
!

• Work in progress: is theconnection significant.
16Other FSRQs:
3C279• In 2007: radio+rotation+VHE• In 2014-2015
Major flaring in Fermi-band(Hayashida et al. 2015, Fermi Collaboration 2016)

Radio picture very
complicatedNo rotations in EVPA
No major flares in VHE?
• Work in progress
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FSRQ PKS1441+25 at z=0.94• Slow increase of flux
• Something “pushing” theenergy dissipation region“out”?

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Conclusions●

Currently many open questions on VHE gamma-ray
emission of FSRQs:emission siteseed photons for IC scattering
fast variability
low state VHE emission●Long-term monitoring observations with goodsensitivity below 100 GeV mandatory to solve thepuzzle
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