scholarly journals A stratified jet model for AGN emission in the two-flow paradigm

2018 ◽  
Vol 620 ◽  
pp. A41
Author(s):  
T. Vuillaume ◽  
G. Henri ◽  
P.-O. Petrucci
Keyword(s):  
Energy Distribution ◽  
Thermal Emission ◽  
Lorentz Factor ◽  
High Energy ◽  
Physical Parameters ◽  
Detailed Model ◽  
Pair Plasma ◽  
Analytical Approximations ◽  
Electron Positron ◽  
Inverse Compton

Context. High-energy emission of extragalactic objects is known to take place in relativistic jets, but the nature, the location, and the emission processes of the emitting particles are still unknown. One of the models proposed to explain the formation of relativistic ejections and their associated non-thermal emission is the two-flow model, where the jets are supposed to be composed of two different flows, a mildly relativistic baryonic jet surrounding a fast, relativistically moving electron positron plasma. Here we present the simulation of the emission of such a structure taking into account the main sources of photons that are present in active galactic nuclei (AGNs). Aims. We try to reproduce the broadband spectra of radio-loud AGNs with a detailed model of emission taking into account synchrotron and inverse-Compton emission by a relativistically moving beam of electron positron, heated by a surrounding turbulent baryonic jet. Methods. We compute the density and energy distribution of a relativistic pair plasma all along a jet, taking into account the synchrotron and inverse-Compton process on the various photon sources present in the core of the AGN, as well as the pair creation and annihilation processes. We use semi-analytical approximations to quickly compute the inverse-Compton process on a thermal photon distribution with any anisotropic angular distribution. The anisotropy of the photon field is also responsible for the bulk acceleration of the pair plasma through the “Compton rocket” effect, thus imposing the plasma velocity along the jet. As an example, the simulated emerging spectrum is compared to the broadband emission of 3C 273. Results. In the case of 3C 273, we obtain an excellent fit of the average broadband energy distribution by assuming physical parameters compatible with known estimates. The asymptotic bulk Lorentz factor is lower than what is observed by superluminal motion, but the discrepancy could be solved by assuming different acceleration profiles along the jet.

scholarly journals Magnetic energy dissipation and origin of non-thermal spectra in radiatively efficient relativistic sources

2019 ◽  
Vol 491 (3) ◽  
pp. 3900-3907 ◽  
Author(s):  
E Sobacchi ◽  
Y E Lyubarsky
Keyword(s):  
Energy Distribution ◽  
Magnetic Energy ◽  
Strong Electric Field ◽  
Spectral Energy Distribution ◽  
Lorentz Factor ◽  
High Energy ◽  
Local Magnetic Field ◽  
Spectral Energy ◽  
Electron Mass ◽  
Electron Positron

ABSTRACT The dissipation of turbulent magnetic fields is an appealing scenario to explain the origin of non-thermal particles in high-energy astrophysical sources. However, it has been suggested that the particle distribution may effectively thermalize when the radiative (synchrotron and/or Inverse Compton) losses are severe. Inspired by recent particle-in-cell simulations of relativistic turbulence, which show that electrons are impulsively heated in intermittent current sheets by a strong electric field aligned with the local magnetic field, we instead argue that in plasmas where the particle number density is dominated by the pairs (electron–positron and electron–positron–ion plasmas): (i) as an effect of fast cooling and of different injection times, the electron energy distribution is dne/dγ ∝ γ−2 for γ ≲ γheat (the Lorentz factor γheat being close to the equipartition value), while the distribution steepens at higher energies; (ii) since the time-scales for the turbulent fields to decay and for the photons to escape are of the same order, the magnetic and the radiation energy densities in the dissipation region are comparable; (iii) if the mass energy of the plasma is dominated by the ion component, the pairs with a Lorentz factor smaller than a critical one (of the order of the proton-to-electron mass ratio) become isotropic, while the pitch angle remains small otherwise. The outlined scenario is consistent with the typical conditions required to reproduce the spectral energy distribution of blazars, and allows one to estimate the magnetization of the emission site. Finally, we show that turbulence within the Crab Nebula may power the observed gamma-ray flares if the pulsar wind is nearly charge separated at high latitudes.

scholarly journals Gamma rays from jets interacting with BLR clouds in blazars

2019 ◽  
Vol 623 ◽  
pp. A101 ◽  
Author(s):  
S. del Palacio ◽  
V. Bosch-Ramon ◽  
G. E. Romero
Keyword(s):  
Thermal Emission ◽  
Strong Shock ◽  
High Energy ◽  
Broad Line ◽  
High Energy Radiation ◽  
Broad Line Region ◽  
Photon Field ◽  
Cloud Dynamics ◽  
Line Region ◽  
Inverse Compton

Context. The innermost parts of powerful jets in active galactic nuclei are surrounded by dense, high-velocity clouds from the broad-line region, which may penetrate into the jet and lead to the formation of a strong shock. Such jet-cloud interactions are expected to have measurable effects on the γ-ray emission from blazars. Aims. We characterise the dynamics of a typical cloud-jet interaction scenario, and the evolution of its radiative output in the 0.1–30 GeV energy range, to assess to what extent these interactions can contribute to the γ-ray emission in blazars. Methods. We use semi-analytical descriptions of the jet-cloud dynamics, taking into account the expansion of the cloud inside the jet and its acceleration. Assuming that electrons are accelerated in the interaction and making use of the hydrodynamical information, we then compute the high-energy radiation from the cloud, including the absorption of γ-rays in the ambient photon field through pair creation. Results. Jet-cloud interactions can lead to significant γ-ray fluxes in blazars with a broad-line region (BLR), in particular when the cloud expansion and acceleration inside the jet are taken into account. This is caused by 1) the increased shocked area in the jet, which leads to an increase in the energy budget for the non-thermal emission; 2) a more efficient inverse Compton cooling with the boosted photon field of the BLR; and 3) an increased observer luminosity due to Doppler boosting effects. Conclusions. For typical broad-line region parameters, either (i) jet-cloud interactions contribute significantly to the persistent γ-ray emission from blazars or (ii) the BLR is far from spherical or the fraction of energy deposited in non-thermal electrons is small.

scholarly journals Kinetic beaming in radiative relativistic magnetic reconnection: a mechanism for rapid gamma-ray flares in jets

2020 ◽  
Vol 498 (1) ◽  
pp. 799-820 ◽  
Author(s):  
J M Mehlhaff ◽  
G R Werner ◽  
D A Uzdensky ◽  
M C Begelman
Keyword(s):  
Magnetic Reconnection ◽  
Gamma Ray ◽  
Critical Role ◽  
High Energy ◽  
Particle In Cell ◽  
Pair Plasma ◽  
Spectrum Radio ◽  
Inverse Compton ◽  
Emission Models ◽  
The One

ABSTRACT Rapid gamma-ray flares pose an astrophysical puzzle, requiring mechanisms both to accelerate energetic particles and to produce fast observed variability. These dual requirements may be satisfied by collisionless relativistic magnetic reconnection. On the one hand, relativistic reconnection can energize gamma-ray emitting electrons. On the other hand, as previous kinetic simulations have shown, the reconnection acceleration mechanism preferentially focuses high energy particles – and their emitted photons – into beams, which may create rapid blips in flux as they cross a telescope’s line of sight. Using a series of 2D pair-plasma particle-in-cell simulations, we explicitly demonstrate the critical role played by radiative (specifically inverse Compton) cooling in mediating the observable signatures of this ‘kinetic beaming’ effect. Only in our efficiently cooled simulations do we measure kinetic beaming beyond one light crossing time of the reconnection layer. We find a correlation between the cooling strength and the photon energy range across which persistent kinetic beaming occurs: stronger cooling coincides with a wider range of beamed photon energies. We also apply our results to rapid gamma-ray flares in flat-spectrum radio quasars, suggesting that a paradigm of radiatively efficient kinetic beaming constrains relevant emission models. In particular, beaming-produced variability may be more easily realized in two-zone (e.g. spine-sheath) set-ups, with Compton seed photons originating in the jet itself, rather than in one-zone external Compton scenarios.

scholarly journals Inverse-Compton scattering in the resolved jet of the high-redshift quasar PKS J1421−0643

2020 ◽  
Vol 497 (1) ◽  
pp. 988-1000 ◽  
Author(s):  
D M Worrall ◽  
M Birkinshaw ◽  
H L Marshall ◽  
D A Schwartz ◽  
A Siemiginowska ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Redshift ◽  
Lorentz Factor ◽  
High Energy ◽  
Radio Spectrum ◽  
X Rays ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Jet Power

ABSTRACT Despite the fact that kpc-scale inverse-Compton (iC) scattering of cosmic microwave background (CMB) photons into the X-ray band is mandated, proof of detection in resolved quasar jets is often insecure. High redshift provides favourable conditions due to the increased energy density of the CMB, and it allows constraints to be placed on the radio synchrotron-emitting electron component at high energies that are otherwise inaccessible. We present new X-ray, optical, and radio results from Chandra, HST, and the VLA for the core and resolved jet in the z = 3.69 quasar PKS J1421−0643. The X-ray jet extends for about 4.5 arcsec (32 kpc projected length). The jet’s radio spectrum is abnormally steep and consistent with electrons being accelerated to a maximum Lorentz factor of about 5000. Results argue in favour of the detection of iC X-rays for modest magnetic field strength of a few nT, Doppler factor of about 4, and viewing angle of about 15°, and predict the jet to be largely invisible in most other spectral bands including the far- and mid-infrared and high-energy gamma-ray. The jet power is estimated to be about 3 × 1046 erg s−1 which is of order a tenth of the quasar bolometric power, for an electron–positron jet. The jet radiative power is only about 0.07 per cent of the jet power, with a smaller radiated power ratio if the jet contains heavy particles, so most of the jet power is available for heating the intergalactic medium.

scholarly journals Time evolution of the spectral break in the high-energy extra component of GRB 090926A

2017 ◽  
Vol 606 ◽  
pp. A93 ◽  
Author(s):  
M. Yassine ◽  
F. Piron ◽  
R. Mochkovitch ◽  
F. Daigne
Keyword(s):  
Time Evolution ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
High Energy ◽  
Pair Creation ◽  
Spectral Break ◽  
Broadband Spectrum ◽  
Inverse Compton ◽  
Spectral Attenuation ◽  
Prompt Emission

Aims. The prompt light curve of the long GRB 090926A reveals a short pulse ~10 s after the beginning of the burst emission, which has been observed by the Fermi observatory from the keV to the GeV energy domain. During this bright spike, the high-energy emission from GRB 090926A underwent a sudden hardening above 10 MeV in the form of an additional power-law component exhibiting a spectral attenuation at a few hundreds of MeV. This high-energy break has been previously interpreted in terms of gamma-ray opacity to pair creation and has been used to estimate the bulk Lorentz factor of the outflow. In this article, we report on a new time-resolved analysis of the GRB 090926A broadband spectrum during its prompt phase and on its interpretation in the framework of prompt emission models. Methods. We characterized the emission from GRB 090926A at the highest energies with Pass 8 data from the Fermi Large Area Telescope (LAT), which offer a greater sensitivity than any data set used in previous studies of this burst, particularly in the 30−100 MeV energy band. Then, we combined the LAT data with the Fermi Gamma-ray Burst Monitor (GBM) in joint spectral fits to characterize the time evolution of the broadband spectrum from keV to GeV energies. We paid careful attention to the systematic effects that arise from the uncertainties on the LAT response. Finally, we performed a temporal analysis of the light curves and we computed the variability timescales from keV to GeV energies during and after the bright spike. Results. Our analysis confirms and better constrains the spectral break, which has been previously reported during the bright spike. Furthermore, it reveals that the spectral attenuation persists at later times with an increase of the break characteristic energy up to the GeV domain until the end of the prompt phase. We discuss these results in terms of keV−MeV synchroton radiation of electrons accelerated during the dissipation of the jet energy and inverse Compton emission at higher energies. We interpret the high-energy spectral break as caused by photon opacity to pair creation. Requiring that all emissions are produced above the photosphere of GRB 090926A, we compute the bulk Lorentz factor of the outflow, Γ. The latter decreases from 230 during the spike to 100 at the end of the prompt emission. Assuming, instead, that the spectral break reflects the natural curvature of the inverse Compton spectrum, lower limits corresponding to larger values of Γ are also derived. Combined with the extreme temporal variability of GRB 090926A, these Lorentz factors lead to emission radii R ~ 1014 cm, which are consistent with an internal origin of both the keV−MeV and GeV prompt emissions.

Study the Effect of Heavy Elements Nanoparticles in the Photons Energy Spectrum in a Tissue-Equivalent Medium

2017 ◽  
Vol 265 ◽  
pp. 428-433
Author(s):  
V.V. Temchenko ◽  
V.N. Kustov ◽  
Ksenya Sergeevna Lukуanenko
Keyword(s):  
Gold Nanoparticles ◽  
Energy Spectrum ◽  
Energy Distribution ◽  
High Energy ◽  
Heavy Elements ◽  
Tissue Equivalent ◽  
Electron Positron

The effect of the tantalum, platinum and gold nanoparticles on the energy distribution of the high-energy photons in the tissue-equivalent media is studied. It was shown that the presence of nanoparticles results in emergence in the medium of the electron-positron pairs manifesting in the decrease in the number of the primary photons and emergence of the secondary photons with energies of 511 keV and lower.

scholarly journals Comptonization by reconnection plasmoids in black hole coronae I: Magnetically dominated pair plasma

2021 ◽  
Author(s):  
Navin Sridhar ◽  
Lorenzo Sironi ◽  
Andrei M Beloborodov
Keyword(s):  
Black Holes ◽  
High Energy ◽  
Particle Energy ◽  
X Rays ◽  
Particle In Cell ◽  
Pair Plasma ◽  
Electron Positron ◽  
High Energy Tail ◽  
Hard State ◽  
Magnetic Tension

Abstract We perform two-dimensional particle-in-cell simulations of reconnection in magnetically dominated electron-positron plasmas subject to strong Compton cooling. We vary the magnetization σ ≫ 1, defined as the ratio of magnetic tension to plasma inertia, and the strength of cooling losses. Magnetic reconnection under such conditions can operate in magnetically dominated coronae around accreting black holes, which produce hard X-rays through Comptonization of seed soft photons. We find that the particle energy spectrum is dominated by a peak at mildly relativistic energies, which results from bulk motions of cooled plasmoids. The peak has a quasi-Maxwellian shape with an effective temperature of ∼100 keV, which depends only weakly on the flow magnetization and the strength of radiative cooling. The mean bulk energy of the reconnected plasma is roughly independent of σ, whereas the variance is larger for higher magnetizations. The spectra also display a high-energy tail, which receives ∼25 per cent of the dissipated reconnection power for σ = 10 and ∼40 per cent for σ = 40. We complement our particle-in-cell studies with a Monte Carlo simulation of the transfer of seed soft photons through the reconnection layer, and find the escaping X-ray spectrum. The simulation demonstrates that Comptonization is dominated by the bulk motions in the chain of Compton-cooled plasmoids and, for σ ∼ 10, yields a spectrum consistent with the typical hard state of accreting black holes.

scholarly journals GAMMA-RAY EMISSION OF RELATIVISTIC JETS AS A SUPERCRITICAL PROCESS

2008 ◽  
Vol 17 (09) ◽  
pp. 1611-1617 ◽  
Author(s):  
B. E. STERN ◽  
J. POUTANEN
Keyword(s):  
Gamma Ray ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
High Energy ◽  
Relativistic Fluids ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Astrophysical Objects ◽  
Particle Propagation ◽  
The Impact

Supercriticality of the same kind as that in a nuclear pile can take place in high-energy astrophysical objects producing a number of impressive effects. For example, it could cause an explosive release of the energy of a cloud of ultrarelativistic protons into radiation. More certainly, supercriticality should be responsible for energy dissipation of very energetic relativistic fluids such as ultrarelativistic shocks in gamma-ray bursts and jets in active galactic nuclei (AGNs). In this case, the photon breeding process operates. It is a kind of converter mechanism with the high-energy photons and e+e- pairs converting into each other via pair production and inverse Compton scattering. Under certain conditions, which should be satisfied in powerful AGNs, the photon breeding mechanism becomes supercritical: the high-energy photons breed exponentially until their feedback on the fluid changes its velocity pattern. Then the system comes to a self-adjusting near-critical steady state. Monte-Carlo simulations with detailed treatment of particle propagation and interactions demonstrate that a jet with a Lorentz factor Γ ≈ 20 can radiate away up to a half of its total energy, and for Γ = 40 the radiation efficiency can be up to 80 per cent. Outer layers of the jet decelerate down to a moderate Lorentz factor 2–4, while the spine of the jet has a final Lorentz factor in the range 10–20 independent of the initial Γ. Such sharp deceleration under the impact of radiation must cause a number of interesting phenomena such as formation of internal shocks and an early generation of turbulence.

Dense Electron-Positron Pair Plasma Expansion

2015 ◽  
Vol 70 (10) ◽  
pp. 875-880
Author(s):  
Mourad Djebli
Keyword(s):  
High Energy ◽  
Expansion Velocity ◽  
Exchange Correlation ◽  
Two Fluids ◽  
Pair Plasma ◽  
Electron Positron ◽  
Correlation Potential ◽  
Energy Laser ◽  
High Energy Laser ◽  
Electron Positron Pair

AbstractThe expansion of an electron-positron plasma is studied based on quantum hydrodynamical equations for two fluids. The quasi-neutral expansion, depicted through the quantum screening distance, is investigated numerically when the annealing processes is very slow. It was found that the pair plasma behaves as a single fluid with a front expansion velocity that depends on the density and degenerate parameters. Faster expansion results from the existence of exchange-correlation potential, which is enhanced in high-density plasma. The present investigation may be useful in understanding the expansion of a dense plasma produced by the interaction between high-energy laser and solid targets.

scholarly journals Electron–positron pair plasma in TXS 0506+056 and the ‘neutrino flare’ in 2014–2015

2020 ◽  
Vol 497 (4) ◽  
pp. 5318-5325
Author(s):  
N Fraija ◽  
E Aguilar-Ruiz ◽  
A Galván-Gámez
Keyword(s):  
Gamma Ray ◽  
Neutrino Flux ◽  
High Energy ◽  
Electron Mass ◽  
Pair Plasma ◽  
Electron Positron ◽  
Accelerated Protons ◽  
Temporal And Spatial ◽  
Electron Positron Pair ◽  
Simultaneous Activity

ABSTRACT The detection of a prolonged flaring activity from blazar TXS 0506+056 in temporal and spatial coincidence with the energetic neutrino IceCube-170922A provided evidence about the photohadronic interactions in this source. However, analysis of the archival neutrino and multiwavelength data from the direction of this blazar between 2014 September and 2015 March revealed a ‘neutrino flare’ without observing quasi-simultaneous activity in the gamma-ray bands, posing challenges to established models. Electron–positron (e±) pairs generated from the accretion discs have been amply proposed as a mechanism of bulk acceleration of sub-relativistic and relativistic jets. These pairs annihilate inside the source producing a line around the electron mass, which is blueshifted in the observed frame (on Earth) and redshifted in the frame of the dissipation region of the jet. The redshifted photons in the dissipation region interact with accelerated protons, producing high-energy neutrinos that contribute significantly to the diffuse neutrino flux in the ∼10–20 TeV energy range in connection with gamma-rays from the photopion process, which can be detected by future MeV orbiting satellites. Based on this phenomenological model, we can explain the ‘neutrino flare’ reported in 2014–1015.

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