Inverse Compton Cascades in Pair-producing Gaps: Effects of Triplet Pair Production

Πετροπούλου, Μαρία; Yuan, Yajie; Chen, Alexander Y.; Mastichiadis, A.

doi:10.3847/1538-4357/ab3856

Cited by 7 publications

(2 citation statements)

References 42 publications

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“…Any imbalance in the supply of charged particles, however, results in the immediate creation of vacuum (electrostatic) gaps. In vacuum gaps the actual charge density, provided by photon-photon PP (see, however, Petropoulou et al 2019, for an assessment of the importance of triplet PP in limiting the gap growth), is different from the Goldreich-Julian charge density. Because of this deviation, the force-free condition is not satisfied and the electric field component parallel to the magnetic field lines is non-vanishing and able to accelerate intruding charge carriers to relativistic velocities, extracting energy from the central rotating BH (Blandford & Znajek 1977;Beskin et al 1992;Hirotani & Okamoto 1998;Levinson 2000).…”

Section: Introductionmentioning

confidence: 99%

Electron-beam interaction with emission-line clouds in blazars

Wendel

González

Paneque

et al. 2021

A&A

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Context. An electron-positron beam escaping from the magnetospheric vacuum gap of an accreting black hole interacts with recombination-line photons from surrounding gas clouds. Inverse-Compton scattering and subsequent pair production initiate unsaturated electromagnetic cascades exhibiting a characteristic spectral energy distribution. Aims. By modelling the interactions of beam electrons (positrons) with hydrogen and helium recombination-line photons, we seek to describe the spectral signature of beam-driven cascades in the broad emission-line region of blazar jets. Methods. Employing coupled kinetic equations for electrons (positrons) and photons including an escape term, we numerically obtained their steady-state distributions and the escaping photon spectrum. Results. We find that cascade emission resulting from beam interactions can produce a narrow spectral feature at TeV energies. Indications of such an intermittent feature, which defies an explanation in the standard shock-in-jet scenario, have been found at ≈ 4σ confidence level at an energy of ≈ 3 TeV in the spectrum of the blazar Mrk 501. Conclusions. The energetic requirements for explaining the intermittent 3 TeV bump with the beam-interaction model are plausible: Gap discharges that lead to multi-TeV beam electrons (positrons) carrying ≈ 0.1% of the Blandford-Znajek luminosity, which interact with recombination-line photons from gas clouds that reprocess ≈ 1% of the similar accretion luminosity are required.

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Section: Introductionmentioning

confidence: 99%

Electron-beam interaction with emission-line clouds in blazars

Wendel

González

Paneque

et al. 2021

A&A

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“…The nonthermal processes occurring in the vicinity of supermassive black holes (BHs) have attracted considerable attention in recent times (e.g., Hirotani et al , 2017Levinson & Segev 2017;Hirotani 2018;Ford et al 2018;Levinson & Cerutti 2018;Katsoulakos & Rieger 2018;Chen et al 2018;Petropoulou et al 2019). The formation of strong electromagnetic fields in charge-deficient regions (aka gaps) around rotating BHs is thought to facilitate efficient particle acceleration to very high energies (VHEs), in the case of hadrons possibly even up to ultrahigh (≥ 10 18 eV) energies (see Rieger 2019, for a review).…”

Section: Introductionmentioning

confidence: 99%

Gap-type Particle Acceleration in the Magnetospheres of Rotating Supermassive Black Holes

Katsoulakos,

Rieger

2020

Preprint

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The detection of rapidly variable gamma-ray emission in active galactic nuclei (AGN) has generated renewed interest in magnetospheric particle acceleration and emission scenarios. In order to explore its potential, we study the possibility of steady gap acceleration around the null surface of a rotating black hole magnetosphere. We employ a simplified (1D) description along with the general relativistic expression of Gauss's law, and we assume that the gap is embedded in the radiation field of a radiatively inefficient accretion flow. The model is used to derive expressions for the radial distribution of the parallel electric field component, the electron and positron charge density, the particle Lorentz factor, and the number density of γ-ray photons. We integrate the set of equations numerically, imposing suitable boundary conditions. The results show that the existence of a steady gap solution for a relative high value of the global current is in principle possible if charge injection of both species is allowed at the boundaries. We present gap solutions for different choices of the global current and the accretion rate. When put in context, our results suggest that the variable very high energy γ-ray emission in M87 could be compatible with a magnetospheric origin.

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TeV pion bumps in the gamma-ray spectra of flaring blazars

Petropoulou,

Mastichiadis,

Vasilopoulos

et al. 2024

A&A

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Very high-energy (VHE, $E>100$ GeV) observations of the blazar Mrk 501 with MAGIC in 2014 provided evidence for an unusual narrow spectral feature at about 3 TeV during an extreme X-ray flaring activity. The one-zone synchrotron-self Compton scenario, widely used in blazar broadband spectral modeling, fails to explain the narrow TeV component. Motivated by this rare observation, we propose an alternative model for the production of narrow features in the VHE spectra of flaring blazars. These spectral features may result from the decay of neutral pions ($ bumps) that are in turn produced via interactions of protons (of tens of TeV energy) with energetic photons, whose density increases during hard X-ray flares. We explored the conditions needed for the emergence of narrow $ bumps in VHE blazar spectra during X-ray flares reaching synchrotron energies $ 100$ keV using time-dependent radiative transfer calculations. We focused on high-synchrotron peaked (HSP) blazars, which comprise the majority of VHE-detected extragalactic sources. We find that synchrotron-dominated flares with peak energies $ keV can be ideal periods for the search of $ bumps in the VHE spectra of HSP blazars. The flaring region is optically thin to photopion production, its energy content is dominated by the relativistic proton population, and the inferred jet power is highly super-Eddington. Application of the model to the spectral energy distribution of Mrk 501 on MJD 56857.98 shows that the VHE spectrum of the flare is described well by the sum of a synchrotron self-Compton (SSC) component and a distinct $ bump centered at 3 TeV. Spectral fitting of simulated SSC+$ spectra for the Cherenkov Telescope Array (CTA) show that a $ bump could be detected at a 5sigma significance level with a 30-min exposure. A harder VHE gamma -ray spectrum than the usual SSC prediction or, more occasionally, a distinct narrow bump at VHE energies during hard X-ray flares, can be suggestive of a relativistic hadronic component in blazar jets that otherwise would remain hidden. The production of narrow features or spectral hardenings due to $ decay in the VHE spectra of blazars is testable with the advent of CTA.

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Inverse Compton Cascades in Pair-producing Gaps: Effects of Triplet Pair Production

Cited by 7 publications

References 42 publications

Electron-beam interaction with emission-line clouds in blazars

Electron-beam interaction with emission-line clouds in blazars

Gap-type Particle Acceleration in the Magnetospheres of Rotating Supermassive Black Holes

TeV pion bumps in the gamma-ray spectra of flaring blazars

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