GeV BREAKS IN BLAZARS AS A RESULT OF GAMMA-RAY ABSORPTION WITHIN THE BROAD-LINE REGION

Poutanen, Juri; Stern, B. E.

doi:10.1088/2041-8205/717/2/l118

Cited by 238 publications

(277 citation statements)

References 27 publications

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“…Furthermore, Jorstad et al (2001Jorstad et al ( , 2010 found that γ-ray flares often occur after superluminal knots have separated away from the VLBI core. The results presented here support the inference that γ-ray emission still occurs parsecs downstream of the central engine, in contrast to conclusions based on theoretical arguments (e.g., Tavecchio et al 2010;Poutanen & Stern 2010). These arguments place the γ-ray emission zones within the broad-line region (BLR) at distances of < ∼ 1 pc from the central engine.…”

Section: Discussionsupporting

confidence: 73%

Relativistic outflow drivesγ-ray emission in 3C 345

Schinzel

Lobanov

Taylor

et al. 2012

A&A

100

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Aims. On the basis of the first 20 months of Fermi-LAT data and optical monitoring, the quasar 3C 345 has been identified as a γ-ray emitter. We investigate whether there is a connection between the γ-ray and optical variability of 3C 345 and the properties of its parsec-scale radio emission. Methods. We combined the Fermi-LAT data of 3C 345, covering an energy range of 0.1-300 GeV, with 32 Very Long Baseline Array observations of the object made at 43.2 GHz in the period of January 2008-March 2010.Results. The VLBA data reveal the morphology and kinematics of the flow on scales of up to ≈5 milliarcseconds (deprojected linear distances of 380 parsecs). The brightness temperature, T b (r), measured along the jet first decreases with distance ∝r −(0.95 ± 0.69) and later exhibits a break at ≈0.3 milliarcseconds (mas), with T b (r) ∝ r −(4.11 ± 0.85) at larger separations. Variations in the γ-ray, optical, and parsec-scale radio emission display a similar long-term trend that persists during the entire VLBA monitoring period. The γ-ray and optical variations on shorter timescales are related to structural changes in the jet on scales of ≈0.3 mas (≈23 parsecs, deprojected), with the γ-ray and optical flares possibly being related to the evolution of four distinct superluminal components identified in the flow. Conclusions. The observations indicate that both the quiescent and flaring components of the γ-ray emission are produced in a region of the jet that extends up to ∼23 pc. This region may correspond to the Compton-loss dominated zone of the flow and its large extent may favor the synchrotron self-Compton mechanism for γ-ray production in the relativistic jet of the quasar 3C 345.

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Section: Discussionsupporting

confidence: 73%

Relativistic outflow drivesγ-ray emission in 3C 345

Schinzel

Lobanov

Taylor

et al. 2012

A&A

100

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“…less than one tenth of parsec (e.g. Finke & Dermer 2010;Ghisellini et al 2010;Poutanen & Stern 2010;Tavecchio et al 2010). In order to distinguish between the two hypotheses, we have followed the argument on the electrons cooling time as explained in Tavecchio et al (2010).…”

Section: Discussionmentioning

confidence: 99%

Search for the shortest variability at gamma rays in flat-spectrum radio quasars

Foschini

Ghisellini

Tavecchio

et al. 2011

A&A

126

116

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We report about the search for short-term variability in the high-energy γ-ray energy band of three flat-spectrum radio quasars (3C 454.3, 3C 273, PKS B1222+216), whose flux at E > 100 MeV exceeded the value of 10 −5 ph cm −2 s −1 for at least one day. Although, the statistics was not yet sufficient to effectively measure the characteristic time scale, it allowed us to set tight upper limits on the observed doubling time scale (<2-3 h) -the smallest measured to date at MeV energies -, which can constrain the size of the γ-ray emitting region. The results obtained in the present work favor the hypothesis that γ rays are generated inside the broad-line region.

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“…The spectral slope becomes steeper near a break energy of about several GeV. Qualitatively such details are well explained by pair-production opacity created by individual bright spectral lines and sharp spectral edges (Poutanen & Stern 2010;Stern & Poutanen 2014) in the far and extreme UV range. Such spectral details are naturally produced by the c 2016 RAS BLR responsible for the broad components of emission lines.…”

Section: Introductionmentioning

confidence: 87%

“…The spectra of FSRQ and bright (low-synchrotronpeak) BL Lacs obtained by the Large Area Telescope onboard of the Fermi Gamma-ray Space Telescope (Fermi/LAT) in the 0.1−30 GeV energy range reveal strong deviations from any smooth (single power-law or log-normal) spectral model (Abdo et al 2010;Poutanen & Stern 2010;Tanaka et al 2011;Stern & Poutanen 2011. Unlike the fainter BL Lac objects lacking observable disc and line emission, a nearly power-law spectrum observed in FSRQs in the 1 GeV range cannot be extrapolated to energies higher than several GeV.…”

Section: Introductionmentioning

confidence: 99%

Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars

Abolmasov

Poutanen

2016

Mon. Not. R. Astron. Soc.

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The GeV-range spectra of blazars are shaped not only by non-thermal emission processes internal to the relativistic jet but also by external pair-production absorption on the thermal emission of the accretion disc and the broad-line region (BLR). For the first time, we compute here the pair-production opacities in the GeV range produced by a realistic BLR accounting for the radial stratification and radiation anisotropy. Using photoionization modelling with the CLOUDY code, we calculate a series of BLR models of different sizes, geometries, cloud densities, column densities and metallicities. The strongest emission features in the model BLR are Lyα and He II Lyα. Contribution of recombination continua is smaller, especially for hydrogen, because Ly continuum is efficiently trapped inside the large optical depth BLR clouds and converted to Lyman emission lines and higher-order recombination continua. The largest effects on the gamma-ray opacity are produced by the BLR geometry and localization of the gamma-ray source. We show that when the gamma-ray source moves further from the central source, all the absorption details move to higher energies and the overall level of absorption drops because of decreasing incidence angles between the gamma-rays and BLR photons. The observed positions of the spectral breaks can be used to measure the geometry and the location of the gamma-ray emitting region relative to the BLR. Strong dependence on geometry means that the soft photons dominating the pair-production opacity may be actually produced by a different population of BLR clouds than the bulk of the observed broad line emission.

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GeV BREAKS IN BLAZARS AS A RESULT OF GAMMA-RAY ABSORPTION WITHIN THE BROAD-LINE REGION

Cited by 238 publications

References 27 publications

Relativistic outflow drivesγ-ray emission in 3C 345

Relativistic outflow drivesγ-ray emission in 3C 345

Search for the shortest variability at gamma rays in flat-spectrum radio quasars

Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars

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