Kiloparsec‐Scale Jets in FR I Radio Galaxies and the γ‐Ray Background

Stawarz, Ł.; Kneiske, T.; Kataoka, J.

doi:10.1086/498084

Cited by 42 publications

(49 citation statements)

References 72 publications

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“…Indeed, the maximum propagation length of the jet electrons emitting 10 keV synchrotron photons within the 100 G jet (equipartition) magnetic field can be estimated as l rad ¼ cÀ t rad $ 10 pc for À $ 2, which clearly indicates the need for the continuous acceleration of the radiating electrons in between the compact knots. Let us mention at this point, that the analysis of the expected -ray emission from kiloparsec-scale FR I jets presented by Stawarz et al (2006) suggests that subequipartition magnetic fields (which could increase l rad ) are not likely in these objects. The problem could disappear if many small-scale strong shocks are present (below the flux resolution limit for our point-source detection), possibly generated at the supersonic and highly turbulent jet boundary layer.…”

Section: The Jetmentioning

confidence: 94%

The X‐Ray Jet in Centaurus A: Clues to the Jet Structure and Particle Acceleration

Kataoka¹,

Stawarz²,

Aharonian³

et al. 2006

ApJ

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We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4 00 , 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flattopped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50 00 and 170 00 . We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of X % 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of X < 0:5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.

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Section: The Jetmentioning

confidence: 94%

The X‐Ray Jet in Centaurus A: Clues to the Jet Structure and Particle Acceleration

Kataoka¹,

Stawarz²,

Aharonian³

et al. 2006

ApJ

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“…The ratio of the cocoon to jet radii is given by ξ c/j = 10 as a reference value [63,64], which leads to R jet = 0.5 kpc. The magnetic fields are assumed to be B jet = 0.3 mG (e.g., [65]) and B coc = 3 µG [66,67]. The expansion velocity of the cocoon is set to v exp = 3000 km s −1 [68].…”

Section: Setup For Monte Carlo Simulationsmentioning

confidence: 99%

Ultrahigh-energy cosmic-ray nuclei from black hole jets: Recycling galactic cosmic rays through shear acceleration

2018

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We perform Monte Carlo simulations of transrelativistic shear acceleration dedicated to a jetcocoon system of active galactic nuclei. A certain fraction of galactic cosmic rays in a halo is entrained, and sufficiently high-energy particles can be injected to the reacceleration process and further accelerated up to 100 EeV. We show that the shear reacceleration mechanism leads to a hard spectrum of escaping cosmic rays,spectrum. The supersolar abundance of ultrahigh-energy nuclei is achieved due to injections at TeV-PeV energies. As a result, we find that the highest-energy spectrum and mass composition can be reasonably explained by our model without contradictions with the anisotropy data.

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“…Contributions from unresolved blazars and MSPs are believed to contribute at least few percent to the Fermi-LAT EGB, while predictions for star-forming galaxies and UHECRs are highly model dependent. Other astrophysical sources may emit in the high latitude γ-ray sky: i) radio-quiet AGN [34,35], and Fanaroff and Riley radio galaxies of type I and II [36][37][38] whose contribution is strongly model dependent and likely bound to few percent of the EGB; ii) γ-ray bursts (GRBs), estimated less than 1% of the diffuse extragalactic γ-ray background [39]; iii) star-burst and luminous infrared galaxies. The relevant flux may cover a significant fraction of the EGB (≤ 20%) [40], but the model dependence is such to prevent firm statements on the relevance of this extragalactic source; iv) nearby clusters of galaxies, which could yield about 1% − 10% of the EGRET EGB [41][42][43]; v) gravitational induced shock waves, produced during cluster mergers and large-scale structure formation, whose fluxes are quite model dependent and may reach few percent [44,45].…”

Section: The Extragalactic γ-Ray Backgroundmentioning

confidence: 99%

Conservative upper limits on WIMP annihilation cross section from Fermi-LATγrays

2012

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The spectrum of an isotropic extragalactic γ-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subtraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain stringent upper limits on their annihilation cross section. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, we consider models for DM annihilation depending on the inverse of the velocity and associate the EGBs to photons arising from the annihilation of DM in primordial halos. Given our choices for the EGB and the minimal DM modelling, the derived upper bounds are claimed to be conservative.PACS numbers: 95.30. Cq,95.35+d,95.85.Pw,96.50.sb

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Kiloparsec‐Scale Jets in FR I Radio Galaxies and the γ‐Ray Background

Cited by 42 publications

References 72 publications

The X‐Ray Jet in Centaurus A: Clues to the Jet Structure and Particle Acceleration

The X‐Ray Jet in Centaurus A: Clues to the Jet Structure and Particle Acceleration

Ultrahigh-energy cosmic-ray nuclei from black hole jets: Recycling galactic cosmic rays through shear acceleration

Conservative upper limits on WIMP annihilation cross section from Fermi-LATγrays

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