An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?

Bonnoli, G.; Tavecchio, F.; Ghisellini, G.; Sbarrato, T.

doi:10.1093/mnras/stv953

Cited by 69 publications

(81 citation statements)

References 67 publications

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“…In this study we focus on a subsample of AGN, the so-called extreme T eV blazars (Bonnoli et al (2015)). Blazars are defined as a class of AGN that has peculiar multi-wavelength properties from radio to γ-ray bands of the spectrum.…”

Section: The Sample Of Blazar Spectramentioning

confidence: 99%

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

Dzhatdoev¹,

Khalikov²,

Kircheva³

et al. 2017

A&A

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Context. Most of the studies on extragalactic γ-ray propagation performed up to now only accounted for primary gamma-ray absorption and adiabatic losses ("absorption-only model"). However, there is growing evidence that this model is oversimplified and must be modified in some way. In particular, it was found that the intensity extrapolated from the optically-thin energy range of some blazar spectra is insufficient to explain the optically-thick part of these spectra. This effect was interpreted as an indication for γ-axion-like particle (ALP) oscillation. On the other hand, there are many hints that a secondary component from electromagnetic cascades initiated by primary γ-rays or nuclei may be observed in the spectra of some blazars. Aims. We study the impact of electromagnetic cascades from primary γ-rays or protons on the physical interpretation of blazar spectra obtained with imaging Cherenkov telescopes. Methods. We use the publicly-available code ELMAG to compute observable spectra of electromagnetic cascades from primary γ-rays. For the case of primary proton, we develop a simple, fast and reasonably accurate hybrid method to calculate the observable spectrum. We perform the fitting of the observed spectral energy distributions (SEDs) with various physical models: the absorptiononly model, the "electromagnetic cascade model" (for the case of primary γ-rays), and several versions of the hadronic cascade model (for the case of primary proton). We distinguish the following species of hadronic cascade models: 1) "basic hadronic model", where it is assumed that the proton beam travels undisturbed by extragalactic magnetic field and that all observable γ-rays are produced by primary protons through photohadronic processes with subsequent development of electromagnetic cascades 2) "intermediate hadronic model", the same as the basic hadronic model, but the primary beam is terminated at some redshift z c 3) "modified hadronic model" that includes the contribution from primary (redshifted and partially absorbed) γ-rays. Results. Electromagnetic cascades show at least two very distinct regimes labeled by the energy of the primary γ-ray (E 0 ): the onegeneration regime for the case of E 0 <10 T eV and the universal regime for E 0 >100 T eV and redshift to the source z s >0.02. Spectral signatures of the observable spectrum for the case of the basic hadronic model, z s = 0.186 and low energy (E<200 GeV) are nearly the same as for purely electromagnetic cascade, but for E>200 GeV the spectrum is much harder for the case of the basic hadronic model. In the framework of the intermediate hadronic model, the observable spectrum depends only slightly on the primary proton energy, but it strongly depends on z c at E>500 GeV. As a rule, both electromagnetic and hadronic cascade models provide acceptable fits to the observed SEDs. We show that the best-fit model intensity in the multi-T eV region of the spectrum in the framework of the electromagnetic cascade model is typically greater than the one for the case of th...

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Section: The Sample Of Blazar Spectramentioning

confidence: 99%

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

Dzhatdoev¹,

Khalikov²,

Kircheva³

et al. 2017

A&A

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“…This scenario predicted that low luminosity BL Lacs should be the bluest blazars, and thus relatively strong TeV emitters. For the same reason, the bluest BL Lacs should not be strong MeV or GeV emitters, and may be missed by all sky surveys in these energy bands (see e.g., [4]). …”

Section: The Blazar Sequence 10mentioning

confidence: 99%

The Blazar Sequence 2.0

Ghisellini

2016

Galaxies

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This paper discusses the spectral energy distribution (SED) of all blazars with redshift detected by the Fermi satellite and listed in the 3LAC catalog. The so called "blazar sequence" from the phenomenological point of view will be updated, with no theory or modelling. It will be shown that: (i) pure data show that jet and accretion power are related; (ii) the updated blazar sequence maintains the properties of the old version, albeit with a less pronounced dominance of the γ-ray emission; (iii) at low bolometric luminosities, two different types of objects have the same high energy power: low black hole mass flat spectrum radio quasars and high mass BL Lacs. Therefore, at low luminosities, there is a very large dispersion of SED shapes; (iv) in low power BL Lacs, the contribution of the host galaxy is important. Remarkably, the luminosity distribution of the host galaxies of BL Lacs are spread in a very narrow range; (v) a simple sum of two smoothly joining power laws can describe the blazar SEDs very well.

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“…In principle, the cascade component could be mimicked by features in the intrinsic blazar spectrum caused by, e.g., multiple γ-rayemitting regions (e.g., Lefa et al 2011a). However, the multiwavelength emission of EHBLs can also be successfully described with one emission zone under the assumption of very high minimal Lorentz factors of the underlying electron distributions or electron distributions with a Maxwellian shape (Katarzyński et al 2006;Tavecchio et al 2009;Kaufmann et al 2011;Lefa et al 2011b;Bonnoli et al 2015). Furthermore, the sensitivity for the cascade has been derived here from a combined likelihood of several sources.…”

Section: Resultsmentioning

confidence: 99%

“…We present our results in Section 5 before concluding in Section 6. ), promising sources also show a high ratio between the X-ray and radio flux,  F F 10 X R 4 , as well as an optical spectrum dominated by the host galaxy (Bonnoli et al 2015). Bonnoli et al used values for the X-ray and radio flux as listed in Plotkin et al (2010) et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of the Cherenkov Telescope Array to the Detection of Intergalactic Magnetic Fields

Meyer

Conrad

Dickinson

2016

ApJ

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Very high energy (VHE; energy E100 GeV) γ-rays originating from extragalactic sources undergo pair production with low-energy photons of background radiation fields. These pairs can inverse-Compton-scatter background photons, initiating an electromagnetic cascade. The spatial and temporal structure of this secondary γ-ray signal is altered as the + -e e pairs are deflected in an intergalactic magnetic field (IGMF). We investigate how VHE observations with the future Cherenkov Telescope Array, with its high angular resolution and broad energy range, can potentially probe the IGMF. We identify promising sources and simulate γ-ray spectra over a wide range of values of the IGMF strength and coherence length using the publicly available ELMAG MonteCarlo code. Combining simulated observations in a joint likelihood approach, we find that current limits on the IGMF can be significantly improved. The projected sensitivity depends strongly on the time a source has been γ-ray active and on the emitted maximum γ-ray energy.

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An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?

Cited by 69 publications

References 67 publications

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

Electromagnetic cascade masquerade: a way to mimicγ-axion-like particle mixing effects in blazar spectra

The Blazar Sequence 2.0

Sensitivity of the Cherenkov Telescope Array to the Detection of Intergalactic Magnetic Fields

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