Possible observation of electromagnetic cascades in extragalactic space

Uryson, A. V.

doi:10.1134/1.558446

Cited by 20 publications

(25 citation statements)

References 9 publications

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“…Uryson (1998) (2016)). We will compare hadronic models with the electromagnetic cascade model of Dzhatdoev (2015b) to reveal their advantages and diffuculties.…”

Section: Introductionmentioning

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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“…Uryson (1998) (2016)). We will compare hadronic models with the electromagnetic cascade model of Dzhatdoev (2015b) to reveal their advantages and diffuculties.…”

Section: Introductionmentioning

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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“…To describe the background radio emission, we used the model of the luminosity evolution for radio galaxies [19]. The magnetic field in intergalactic space is apparently nonuniform [20,21]: there are regions where the magnetic field is 1•10 −17 G < B <3•10 −14 G, and filamentary areas in which the magnetic field is stronger: B ≈10 -9 -10 -8 G. In these fields, the cascade electrons lose their energy through synchrotron radiation insignificantly [22]. However inside galactic clusters the magnetic field possibly is higher, up to B∼10 −6 G [23].…”

Section: The Modelmentioning

confidence: 99%

Ultra-high energy cosmic rays from supermassive black holes: particle flux on the Earth and extragalactic diffuse emission

Uryson

2019

J. Phys.: Conf. Ser.

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Cosmic rays accelerated to ultra-high energies (E >4•10 19 eV) in electric fields in accretion discs around supermassive black holes are discussed. Particle injection spectra are assumed to be harder than those formed in acceleration at shock fronts. It turned out that cosmic rays with injection spectra supposed contribute a little in the particle flux detected with groundbased arrays. But in the extragalactic space particles generate a noticeable flux of the diffuse gamma-ray emission compared with the data obtained with Fermi LAT instrument (onboard the Fermi space observatory). The intensity of neutrinos generated by cosmic rays propagating in the extragalactic space is also derived. The model intensity of cascade neutrinos is much lower than that of astrophysics neutrino. It is concluded that possibly supermassive black holes are cosmic ray sources which contribute slightly to the particle flux detected on the Earth, but these sources should be taken into account analyzing components of extragalactic diffuse gamma-ray emission.

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“…2b. The hadronic cascade model (HCM) [24]- [26] (for more references see [10], [18]) includes a cascade component from SHE and ultra-high energy (UHE, E>1 EeV ) γ-rays and electrons, which, in turn, were produced by a beam of ultra-high energy cosmic rays (CR) by means of Bethe-Heitler pair production (BHPP) Nγ → N ′ e + e − or photohadronic processes (PHP) Nγ → N ′ (n 1 )π + (n 2 )π − (n 3 )π 0 with subsequent decays of pions (here N denotes a proton or nucleus, each number (n 1 , n 2 , n 3 ) may take value 0,1,2,...). In [18] we suggested a further sub-division to distinguish "basic", "intermediate", and "modified" species of the HCM.…”

Section: Pos(icrc2017)866mentioning

confidence: 99%

Extragalactic gamma-ray propagation: beyond the absorption-only model

Dzhatdoev¹,

Khalikov²,

Kircheva³

2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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Observations of extragalactic sources in the high energy (HE, E>100 MeV) and very high energy (VHE, E>100 GeV) domains allow to search for axion-like particles (ALP) and constrain the extragalactic magnetic field (EGMF) parameters. Such studies have recently received much attention thanks to the advent of new instruments and the progress of the extragalactic background light (EBL) models. Observations of blazars indicate that an additional component from electromagnetic (EM) cascades contributes to the observed flux, allowing for a possibility that the EGMF strength in voids of the large scale structure is smaller than 1 fG on the characteristic spatial scale of 1 Mpc. We consider various extragalactic γ-ray propagation models with an emphasis on the "electromagnetic cascade model", which assumes that primary particles are γ-rays, and has the following spectral signatures: 1) a high-energy cutoff caused by the γγ → e + e − absorption process 2) an "ankle" formed by the intersection of the primary and cascade components 3) a possible low-energy "magnetic cutoff", 4) a possible low-energy "second ankle" at the second intersection of the primary and cascade components. The ankle may mimic the signature of the γ-ALP oscillation process. Finally, we consider various species of the "hadronic cascade model", in which primary particles are protons and nuclei. This model has a number of difficulties, but, nevertheless, is not excluded.

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Possible observation of electromagnetic cascades in extragalactic space

Cited by 20 publications

References 9 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

Ultra-high energy cosmic rays from supermassive black holes: particle flux on the Earth and extragalactic diffuse emission

Extragalactic gamma-ray propagation: beyond the absorption-only model

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