scholarly journals Constraining the shear acceleration model for the X-ray emission of large-scale extragalactic jets

2021 ◽  
Author(s):  
F Tavecchio
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Gamma Ray ◽  
Planck Equation ◽  
High Energy ◽  
Ultra High Energy ◽  
Low Frequencies ◽  
X Ray ◽  
High Energy Electrons ◽  
Extragalactic Jets

Abstract The nature of the intense X-ray emission from powerful extragalactic jets at large (>1 kpc) scale is still debated. The scenario that invokes the inverse Compton scattering of the CMB by electrons is challenged by the lack of gamma-ray emission in the GeV band. An alternative assumes synchrotron emission by a distinct population of ultra-high energy electrons. Here we present a concrete attempt to apply this scenario, exploring the specific model in which the ultra-high energy electrons are accelerated in a shear layer surrounding the jet. We limit the study to non-relativistic flows and particle acceleration is treated by a Fokker-Planck equation. The observed relation between low energy (radio, optical) and X-ray emission prompts us to assume that the required population of pre-accelerated particles is provided by a shock responsible for the acceleration of the electrons emitting at low frequencies. We apply the model to the emission of the principal knots of the jets of PKS 0637-752 and PKS 1136-135, two of the best studied objects. For the set of fiducial parameters adopted, the condition that the jet power does not exceeds a limiting value of 1048 erg s−1 constrains the magnetic field above 10 μG and indicates moderate beaming (δ ≃ 2) for PKS 0637-752. For both sources, the requirement that acceleration of the electrons proceeds faster than radiative cooling can be met if the magnetic turbulence in the shear layer follows a Kolmogorov spectrum, I(k)∝k−q with q = 5/3, but cannot satisfied in the Bohm-like case (q = 1).

scholarly journals Symmetric and triangle-shaped variability of blazars

2014 ◽  
Vol 10 (S313) ◽  
pp. 97-98
Author(s):  
Kenji Yoshida
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Low Energy ◽  
Light Curves ◽  
X Ray ◽  
High Energy Electrons ◽  
Flux Variability ◽  
Low Energy Electrons ◽  
Flux Increase ◽  
Rise Phase

AbstractSymmetric and triangle-shaped flux variability in X-ray and gamma-ray light curves is observed from many blazars. We derived the X-ray spectrum changing in time by using a kinetic equation of high energy electrons. Giving linearly changing the injection of low energy electrons into accelerating and emitting region, we obtained the preliminary results that represent the characteristic X-ray variability of the linear flux increase with hardening in the rise phase and the linear decrease with softening in the decay phase.

scholarly journals Interpreting Crab Nebula’s synchrotron spectrum: two acceleration mechanisms

2019 ◽  
Vol 489 (2) ◽  
pp. 2403-2416 ◽  
Author(s):  
Maxim Lyutikov ◽  
Tea Temim ◽  
Sergey Komissarov ◽  
Patrick Slane ◽  
Lorenzo Sironi ◽  
...  
Keyword(s):  
Spectral Index ◽  
Large Scale ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Peak Frequency ◽  
High Energy ◽  
X Rays ◽  
High Energy Electrons ◽  
Astrophysical Objects ◽  
Different Populations

ABSTRACT We outline a model of the Crab pulsar wind nebula with two different populations of synchrotron emitting particles, arising from two different acceleration mechanisms: (i) Component-I due to Fermi-I acceleration at the equatorial portion of the termination shock, with particle spectral index pI ≈ 2.2 above the injection break corresponding to γwindσwind ∼ 105, peaking in the ultraviolet (UV, γwind ∼ 102 is the bulk Lorentz factor of the wind, σwind ∼ 103 is wind magnetization); and (ii) Component-II due to acceleration at reconnection layers in the bulk of the turbulent Nebula, with particle index pII ≈ 1.6. The model requires relatively slow but highly magnetized wind. For both components, the overall cooling break is in the infrared at ∼0.01 eV, so that the Component-I is in the fast cooling regime (cooling frequency below the peak frequency). In the optical band, Component-I produces emission with the cooling spectral index of αo ≈ 0.5, softening towards the edges due to radiative losses. Above the cooling break, in the optical, UV, and X-rays, Component-I mostly overwhelms Component-II. We hypothesize that acceleration at large-scale current sheets in the turbulent nebula (Component-II) extends to the synchrotron burn-off limit of ϵs ∼ 100 MeV. Thus in our model acceleration in turbulent reconnection (Component-II) can produce both hard radio spectra and occasional gamma-ray flares. This model may be applicable to a broader class of high-energy astrophysical objects, like active galactic nuclei and gamma-ray burst jets, where often radio electrons form a different population from the high-energy electrons.

scholarly journals Sunspot Magnetic Fields and High Energy Electrons in Flares

1971 ◽  
Vol 43 ◽  
pp. 390-396
Author(s):  
Tatsuo Takakura
Keyword(s):  
Magnetic Fields ◽  
Electric Potential ◽  
Potential Field ◽  
Large Scale ◽  
Plasma Waves ◽  
High Energy ◽  
Ohmic Loss ◽  
X Ray ◽  
High Energy Electrons ◽  
Electric Potential Field

A balloon observation of an impulsive hard X-ray burst on September 27, 1969 showed the size of the source to be one arc minute or less. It was remarkably smaller than the associated Hα flare with a size of 3 arc min.The efficient acceleration of electrons and the trigger of the flares are suggested to be attributed to a large scale electric potential field caused by a gas motion near the photosphere. The primary cause of the onset of flares would be the acceleration of electrons. The electrons excite plasma waves which make the conductivity lower by several orders, so that the electromagnetic energy I2L stored before the onset of the flare would be suddenly converted into the heat due to the ohmic loss.

scholarly journals ON ACCELERATION AND PROPAGATION OF ULTRA-HIGH ENERGY COSMIC RAYS

2009 ◽  
Vol 18 (10) ◽  
pp. 1583-1586
Author(s):  
MARTIN LEMOINE
Keyword(s):  
Cosmic Rays ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Current Data ◽  
Type I ◽  
Ultra High Energy ◽  
High Energy Cosmic Rays

This paper discusses the correlation reported in 2008 by the Pierre Auger Observatory (PAO) of the arrival directions of the highest energy cosmic rays with active galactic nuclei (AGN). It is argued that these correlating AGN do not have the power required to be the sources of ultra-high energy protons. This current PAO dataset is further shown to disfavor giant radio-galaxies (both Fanaroff–Riley type I and II) as sources of ultra-high energy protons. The current data thus likely point to the local large scale structure, in which the actual sources of ultra-high energy cosmic rays camouflage. Finally, it is shown that the last gamma-ray burst in Centaurus A could explain, through rescattering on the Cen A lobes, the apparent cluster of events in this direction.

scholarly journals High-energy processes in starburst-driven winds

2020 ◽  
Vol 496 (2) ◽  
pp. 2474-2481 ◽  
Author(s):  
Ana L Müller ◽  
Gustavo E Romero ◽  
Markus Roth
Keyword(s):  
Cosmic Rays ◽  
Power Law ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
X Ray ◽  
Star Forming ◽  
Star Forming Regions ◽  
Energy Processes ◽  
Relativistic Particles

ABSTRACT Starburst galaxies generate large-scale winds powered by the activity in the star-forming regions located in the galactic discs. Fragmentation of the disc produced by the outbreak of the wind results in the formation of clouds. Bowshocks caused by the supersonic outflow appear around such clouds. In this paper, we discuss the acceleration of relativistic particles and the production of non-thermal radiation in such scenario. Cosmic rays accelerated at the bowshocks do not reach the highest energies, although the high-energy luminosity generated is significant. We show that up to ∼10 per cent of the gamma-ray emission in starbursts might come from these sources outside the galactic discs. Discrete X-ray sources with a power-law component are also expected.

scholarly journals Observational aspects of AGN jets at high energy

2014 ◽  
Vol 10 (S313) ◽  
pp. 1-11
Author(s):  
Jun Kataoka
Keyword(s):  
Large Scale ◽  
Gamma Ray ◽  
Galactic Center ◽  
Radio Galaxies ◽  
High Energy ◽  
Jet Physics ◽  
Space Telescopes ◽  
Energy Bands ◽  
X Ray ◽  
Astrophysical Jet

AbstractFor the last two decades, significant and dramatic progress has been made in understanding astrophysical jet sources, particularly in the X-ray and gamma-ray energy bands. For example, the Chandra X-ray observatory reveals a number of AGN jets extending from kpc to Mpc scales. More recently, the Fermi Gamma-ray Space Telescopes launched in 2008 started monitoring the gamma-ray sky with excellent sensitivity of about ten times greater than that of EGRET onboard CGRO, and has detected more than 2,000 sources (mostly AGNs) as of 2014. Moreover, Fermi-LAT has discovered gamma-ray emissions not only from blazars but from a dozen radio galaxies not previously known to emit gamma-rays. Closer to home, the Fermi-bubbles were discovered to extend 50 degrees above and below the Galactic center. These large scale diffuse gamma-ray structures are similar in structure to AGN lobes such as those seen in Cen A and provide evidence for past activity in our Galactic center. In this review, I will first summarize recent highlights of large scale jets in radio galaxies, specifically resolved by the Chandra X-ray observatory. Next I will move on to the gamma-ray sky to present some highlights from Fermi-LAT observations of “misaligned” blazars, namely radio galaxies. I will discuss a unification scheme connecting blazars and misaligned radio galaxies. In the last part, I will also briefly comment on recent multiband observations of the Fermi-bubble and possible impacts on the AGN jet physics in the near future.

Hard X-Ray and Gamma-Ray Emission Induced by Ultra-High-Energy Protons in Cluster Accretion Shocks

2005 ◽  
Vol 628 (1) ◽  
pp. L9-L12 ◽  
Author(s):  
Susumu Inoue ◽  
Felix A. Aharonian ◽  
Naoshi Sugiyama
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Ultra High Energy ◽  
X Ray ◽  
Gamma Ray Emission ◽  
Accretion Shocks

scholarly journals Nonthermal emission from the reverse shock of the youngest Galactic supernova remnant G1.9+0.3

2019 ◽  
Vol 627 ◽  
pp. A166 ◽  
Author(s):  
R. Brose ◽  
I. Sushch ◽  
M. Pohl ◽  
K. J. Luken ◽  
M. D. Filipović ◽  
...  
Keyword(s):  
Transport Equation ◽  
Large Scale ◽  
Gas Flow ◽  
Supernova Remnant ◽  
Gamma Ray ◽  
High Energy ◽  
Particle Accelerator ◽  
Sensitivity Threshold ◽  
Reverse Shock ◽  
X Ray

Context. The youngest Galactic supernova remnant G1.9+0.3 is an interesting target for next-generation gamma-ray observatories. So far, the remnant is only detected in the radio and the X-ray bands, but its young age of ≈100 yr and inferred shock speed of ≈14 000 km s−1 could make it an efficient particle accelerator. Aims. We aim to model the observed radio and X-ray spectra together with the morphology of the remnant. At the same time, we aim to estimate the gamma-ray flux from the source and evaluate the prospects of its detection with future gamma-ray experiments. Methods. We performed spherical symmetric 1D simulations with the RATPaC code, in which we simultaneously solved the transport equation for cosmic rays, the transport equation for magnetic turbulence, and the hydro-dynamical equations for the gas flow. Separately computed distributions of the particles accelerated at the forward and the reverse shock were then used to calculate the spectra of synchrotron, inverse Compton, and pion-decay radiation from the source. Results. The emission from G1.9+0.3 can be self-consistently explained within the test-particle limit. We find that the X-ray flux is dominated by emission from the forward shock while most of the radio emission originates near the reverse shock, which makes G1.9+0.3 the first remnant with nonthermal radiation detected from the reverse shock. The flux of very-high-energy gamma-ray emission from G1.9+0.3 is expected to be close to the sensitivity threshold of the Cherenkov Telescope Array. The limited time available to grow large-scale turbulence limits the maximum energy of particles to values below 100 TeV, hence G1.9+0.3 is not a PeVatron.

scholarly journals A Search for Ultra-high-energy Gamma-ray Emission from Binary X-ray Systems

1989 ◽  
Vol 42 (5) ◽  
pp. 581
Author(s):  
PG Edwards ◽  
D Ciampa ◽  
RW Clay ◽  
JR Patterson
Keyword(s):  
Gamma Ray ◽  
Threshold Energy ◽  
High Energy ◽  
Ultra High Energy ◽  
X Ray ◽  
Air Shower ◽  
High Energy Gamma ◽  
Energy Gamma ◽  
Gamma Ray Emission ◽  
The Individual

Observations have been made with the Buckland park air shower array over a two-year period from June 1984. We have examined events from the directions of six binary X-ray systems to search for any periodic component associated with ultra-high-energy gamma-ray emission above a threshold energy of -9xl014 eV. No statistically significant excess has been found and upper limits to the individual fluxes are presented.

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