On the hadronic cascade scenario for extreme BL Lacs

Tavecchio, F.

doi:10.1093/mnras/stt2437

Cited by 41 publications

(43 citation statements)

References 54 publications

(58 reference statements)

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“…Electromagnetic cascades could be the result of the absorption of primary multi-TeV gamma rays or, instead, could be produced by Bethe-Heitler pair creation or photo-meson reactions involving ultra-high energy protons accelerated in the source and beamed toward the Earth. As shown in Tavecchio (2014), the physical parameters of the jets are consistent with the requests of the hadronic cascade scenario, both in terms of maximum hadron energy and jet power. As discussed by Murase et al (2012a) and Takami et al (2013) an effective test to distinguish between intrinsic and reprocessed emission is the observation of photons at several TeV, only possible in the latter case, since the cascade emission, being produced at lower distance, is less affected by absorption than the intrinsic one; although exotic processes such as the photon-axion conversion (e.g.…”

Section: Discussionsupporting

confidence: 75%

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

Bonnoli

Tavecchio

Ghisellini

et al. 2015

Monthly Notices of the Royal Astronomical Society

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High energy observations of extreme BL Lac objects, such as 1ES 0229+200 or 1ES 0347-121, recently focused interest both for blazar and jet physics and for the implication on the extragalactic background light and intergalactic magnetic field estimate. However, the number of these extreme highly peaked BL Lac objects (EHBL) is still rather small. Aiming at increase their number, we selected a group of EHBL candidates starting from the BL Lac sample of Plotkin et al. (2011), considering those undetected (or only barely detected) by the Large Area Telescope onboard Fermi and characterized by a high X-ray vs. radio flux ratio. We assembled the multi-wavelength spectral energy distribution of the resulting 9 sources, profiting of publicly available archival observations performed by Swift, Galex, and Fermi satellites, confirming their nature. Through a simple one-zone synchrotron self-Compton model we estimate the expected VHE flux, finding that in the majority of cases it is within the reach of present generation of Cherenkov arrays or of the forthcoming Cherenkov Telescope Array (CTA).

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Section: Discussionsupporting

confidence: 75%

“…Cerruti et al 2015). A last suggestive possibility is that high-energy photons are produced by ultra-high energy protons along the line of sight injected by the blazars into the intergalactic space (Essey et al 2011;Murase et al 2012a;Zheng & Kang 2013;Tavecchio 2014).…”

Section: Introductionmentioning

confidence: 99%

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

Bonnoli

Tavecchio

Ghisellini

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…Tavecchio (2014) developed such a model (hereafter the T14 model) specifically for the hadronic cascade scenario. In what follows we use the parameters of blazar emission presented in Tavecchio (2014) (Table 2).…”

Section: Constraints On Hadronic Cascade Modelsmentioning

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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“…Mannheim 1993;Dermer & Atoyan 2001;Mücke & Protheroe 2001;Dimitrakoudis et al 2012;Bosch-Ramon et al 2012;Böttcher et al 2013;Mastichiadis et al 2013;Petropoulou et al 2015;Diltz et al 2015 or from interactions of escaping hadrons along the path from the source to Earth (e.g. Essey & Kusenko 2010;Essey et al 2011;Dermer et al 2012;Murase et al 2012;Tavecchio 2014). Contrary to the more commonly assumed leptonic scenarios, in which the two characteristic broad bumps of the non-thermal spectral energy distribution (SED) of blazars are described with electron-synchrotron and Inverse Compton emission (Konigl 1981;Sikora et al 1994), hadronic scenarios introduce relativistic protons to explain the high-energy bump that is generally seen from keV to GeV energies in flat-spectrum radio quasars (FSRQs) and in the MeV to TeV range for BL Lac objects.…”

Section: Introductionmentioning

confidence: 99%

Expected signatures from hadronic emission processes in the TeV spectra of BL Lacertae objects

Zech

Cerruti

Mazin

2017

A&A

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Context. The wealth of recent data from Imaging Air Cherenkov telescopes (IACTs), ultra-high energy cosmic-ray experiments and neutrino telescopes have fuelled a renewed interest in hadronic emission models for γ-loud blazars. Aims. We explore physically plausible solutions for a lepto-hadronic interpretation of the stationary emission from high-frequency peaked BL Lac objects (HBLs). The modelled spectral energy distributions are then searched for specific signatures at very high energies that could help to distinguish the hadronic origin of the emission from a standard leptonic scenario. Methods. By introducing a few basic constraints on parameters of the model, such as assuming the co-acceleration of electrons and protons, we significantly reduced the number of free parameters. We then systematically explored the parameter space of the size of the emission region and its magnetic field for two bright γ-loud HBLs, PKS 2155-304 and Mrk 421. For all solutions close to equipartition between the energy densities of protons and of the magnetic field, and with acceptable jet power and light-crossing timescales, we inspected the spectral hardening in the multi-TeV domain from proton-photon induced cascades and muon-synchrotron emission inside the source. Very-high-energy spectra simulated with the available instrument functions from the future Cherenkov Telescope Array (CTA) were evaluated for detectable features as a function of exposure time, source redshift, and flux level. Results. A range of hadronic scenarios are found to provide satisfactory solutions for the broad band emission of the sources under study. The TeV spectrum can be dominated either by proton-synchrotron emission or by muon-synchrotron emission. The solutions for HBLs cover a parameter space that is distinct from the one found for the most extreme BL Lac objects in an earlier study. Over a large range of model parameters, the spectral hardening due to internal synchrotron-pair cascades, the "cascade bump", should be detectable for acceptable exposure times with the future CTA for a few nearby and bright HBLs.

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On the hadronic cascade scenario for extreme BL Lacs

Cited by 41 publications

References 54 publications

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

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

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

Expected signatures from hadronic emission processes in the TeV spectra of BL Lacertae objects

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