Studying X-ray spectra from large-scale jets of FR II radio galaxies: application of shear particle acceleration

He, Jia-Chun; Sun, Xiao-Na; Wang, Jie-Shuang; Rieger, Frank M; Liu, Ruo-Yu; Liang, En-Wei

doi:10.1093/mnras/stad2542

“…4 Generally, the γ-rays of RGs are still considered to come from the core jet (Fukazawa et al 2015;Xue et al 2017). However, some works studying the X-ray emission of the large-scale jet substructures in RGs predicted the detectable γ-rays of some substructures (e.g., Zhang et al 2009Zhang et al , 2010Zhang et al , 2018He et al 2023). Especially, the detection of γ-rays from large-scale radio lobes of RGs Cen A (Abdo et al 2010a;Sun et al 2016) and Fornax A (Ackermann et al 2016) confirms that the substructures of the jet are acceleration sites of high-energy particles.…”

Section: Introductionmentioning

confidence: 99%

Fermi Large Area Telescope Detection of Gamma Rays from the NGC 6251 Radio Lobe

Yu,

Zhang,

Gan

et al. 2024

ApJ

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We report the detection of extended γ-ray emission from lobes in the radio galaxy NGC 6251 using observation data from the Fermi Large Area Telescope. The maximum likelihood analysis results show that a radio morphology template provides a better fit than a pointlike source description for the observational data at a confidence level of 8.1σ, and the contribution of lobes constitutes more than 50% of the total γ-ray flux. Furthermore, the γ-ray energy spectra show a significant disparity in shape between the core and lobe regions, with a curved log-parabola shape observed in the core region and a power-law form observed in the lobes. Neither the core region nor the northwest (NW) lobe displays significant flux variations in the long-term γ-ray light curves. The broadband spectral energy distributions of the core region and the NW lobe can be explained with a single-zone leptonic model. The γ-rays of the core region are due to the synchrotron-self-Compton process, while the γ-rays from the NW lobe are interpreted as inverse Compton emission of the cosmic microwave background.

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“…The nonthermal radiation observed from AGN jets provides clear evidence for the occurrence of particle acceleration such as those facilitated by, e.g., diffusive shock and/or stochastic Fermi-type processes (e.g., Matthews et al 2020). Shocks are suggested to be responsible for, e.g., the knotted structures in jets such as HST-1 in M87 and the hot spots observed in giant radio lobes and polarization features in blazars (e.g., Blandford et al 2019;Liodakis et al 2022), while stochastic Fermi-type acceleration has been considered to account for the seemingly required hard particle spectra in TeV blazars (Lefa et al 2011;Tavecchio et al 2022; see also (Katarzyński et al 2006) and to provide a promising explanatory framework for understanding the extended, high-energy emission in large-scale AGN jets (e.g., Wang et al 2021;He et al 2023).…”

Section: Introductionmentioning

confidence: 99%

The Role of Stochastic Fermi-type Particle Acceleration in the Inner Jets of Active Galactic Nuclei

Wang,

Rieger,

Mizuno

2024

ApJ

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High-resolution radio observations of nearby active galactic nuclei have revealed extended, limb-brightened structures in their inner jets. This ties in with other multiwavelength observations from radio to X-ray and gamma ray, indicating that a structured jet model is required. While electrons need to be kept energized to account for the observed features, the underlying particle acceleration mechanism is still unclear. We explore the role of stochastic Fermi-type particle acceleration, i.e., classical second-order Fermi and shear acceleration, for understanding the multiwavelength observations of the inner jets of M87. An analytical Fokker–Planck description is adopted to infer characteristic spectral indices and cutoff energies for these two mechanisms. We focus on electron synchrotron radiation as the dominant emission process. We find that the multiwavelength observations of M87 can be satisfactorily accounted for in a framework, where the X-rays are produced at a larger distance from the core than the radio emission region. This provides further support to multizone, broadband emission modeling. We use our findings to also comment on the acceleration of cosmic rays entrained in the sheath.

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“…Scenarios for the acceleration of UHECRs in AGN jets have included particle acceleration at sub-relativistic shocks in the jet-induced backflow in FR II jets (e.g., Matthews et al 2019), second-order Fermi acceleration in turbulent flows in the jet cocoon (e.g., Bicknell & Melrose 1982;Hardcastle 2010), particle acceleration due to cosmic-ray viscosity in relativistic shear flows (e.g., Rieger & Duffy 2004, 2005bWebb et al 2018Webb et al , 2019Webb et al , 2020Rieger 2019;Wang et al 2021Wang et al , 2023, discrete shear acceleration at interfaces between the jet spine and the cocoon backflow (Ostrowski 1998;Kimura et al 2018), turbulent shear acceleration (TSA; Ohira 2013), and the socalled expresso mechanism (Caprioli et al 2015;Mbarek & Caprioli 2019). He et al (2023) applied the shear acceleration model of electrons in radio-jet sources of Rieger & Duffy (2019) and Wang et al (2021), taking into account synchrotron and inverse Compton energy losses. They used the shear acceleration, leaky box model to explain the observations of X-ray spectra in largescale FR II radio sources (e.g.,3C 273,C 403,3C 17,Pictor A,3C 111,and other sources).…”

Section: Introductionmentioning

confidence: 99%

Acceleration and Spectral Redistribution of Cosmic Rays in Radio-jet Shear Flows

Webb,

Xu,

Biermann

et al. 2023

ApJ

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A steady-state, semi-analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity obtained by Webb et al. is generalized to take into account more general cosmic-ray boundary spectra. This involves solving a mixed Dirichlet–Von Neumann boundary value problem at the edge of the jet. The energetic particle distribution function f 0(r, p) at cylindrical radius r from the jet axis (assumed to lie along the z-axis) is given by convolving the particle momentum spectrum f 0 ( ∞ , p ′ ) with the Green’s function G ( r , p ; p ′ ) , which describes the monoenergetic spectrum solution in which f 0 → δ ( p − p ′ ) as r → ∞ . Previous work by Webb et al. studied only the Green’s function solution for G ( r , p ; p ′ ) . In this paper, we explore for the first time, solutions for more general and realistic forms for f 0 ( ∞ , p ′ ) . The flow velocity u = u(r) e z is along the axis of the jet (the z-axis). u is independent of z, and u(r) is a monotonic decreasing function of r. The scattering time τ ( r , p ) = τ 0 ( p / p 0 ) α in the shear flow region 0 < r < r 2, and τ ( r , p ) = τ 0 ( p / p 0 ) α ( r / r 2 ) s , where s > 0 in the region r > r 2 is outside the jet. Other original aspects of the analysis are (i) the use of cosmic ray flow lines in (r, p) space to clarify the particle spatial transport and momentum changes and (ii) the determination of the probability distribution ψ p ( r , p ; p ′ ) that particles observed at (r, p) originated from r → ∞ with momentum p ′ . The acceleration of ultrahigh-energy cosmic rays in active galactic nuclei jet sources is discussed. Leaky box models for electron acceleration are described.

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Studying X-ray spectra from large-scale jets of FR II radio galaxies: application of shear particle acceleration

Cited by 4 publications

References 78 publications

Fermi Large Area Telescope Detection of Gamma Rays from the NGC 6251 Radio Lobe

Fermi Large Area Telescope Detection of Gamma Rays from the NGC 6251 Radio Lobe

The Role of Stochastic Fermi-type Particle Acceleration in the Inner Jets of Active Galactic Nuclei

Acceleration and Spectral Redistribution of Cosmic Rays in Radio-jet Shear Flows

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