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.

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 The Impact of Plasma Instabilities on the Spectra of TeV Blazars

2019 ◽  
Author(s):  
Rafael Alves Batista ◽  
Andrey Saveliev ◽  
Elisabete M de Gouveia Dal Pino
Keyword(s):  
Compton Scattering ◽  
Gamma Ray ◽  
High Energy ◽  
Plasma Instabilities ◽  
Cascade Process ◽  
Extragalactic Background Light ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Very High Energy ◽  
The Impact

Abstract Relativistic jets from blazars are known to be sources of very-high-energy gamma rays (VHEGRs). During their propagation in the intergalactic space, VHEGRs interact with pervasive cosmological photon fields such as the extragalactic background light (EBL) and the cosmic microwave background (CMB), producing electron-positron pairs. These pairs can upscatter CMB/EBL photons to high energies via inverse Compton scattering, thereby continuing the cascade process. This is often used to set limits on intergalactic magnetic fields (IGMFs). However, the picture may change if plasma instabilities, arising due to the interaction of the pairs with the intergalactic medium (IGM), cool down the electrons/positrons faster than inverse Compton scattering. As a consequence, the kinetic energy lost by the pairs to the IGM could cause a hardening in the observed gamma-ray spectrum at energies below ∼100 GeV. Here we study several types and models of instabilities and assess their impact for interpreting observations of distant blazars. Our results suggest that plasma instabilities can describe the spectra of some blazars and mimic the effects of IGMFs, depending on parameters such as intrinsic spectrum of the object, the density and temperature of the IGM, and the luminosity of the beam. On the other hand, we find that for our fiducial set of parameters plasma instabilities do not have a major impact on the spectra of some of the blazars studied. Therefore, they may be used for constraining IGMFs.

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.

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 Gamma-ray emission from pulsar binaries

2012 ◽  
Vol 8 (S291) ◽  
pp. 418-418
Author(s):  
John Kirk ◽  
Iwona Mochol
Keyword(s):  
Magnetic Field ◽  
Binary Systems ◽  
Gamma Ray ◽  
High Energy ◽  
Low Density ◽  
Inverse Compton Scattering ◽  
Poynting Flux ◽  
Inverse Compton ◽  
Shock Precursor ◽  
The Waves

AbstractPulsar winds, containing charged particles, waves and a net (phase-averaged) magnetic field, are thought to fuel the high-energy emission from several gamma-ray binaries. They terminate where the ram pressure matches that of the surroundings - which, in binaries, is provided by the wind of the companion. Before termination, pulsed emission can be produced by inverse Compton scattering of photons from the companion by particles in the waves. After termination, both the bulk kinetic energy of the particles and the Poynting flux in the waves are dissipated into an energetic particle population embedded in the surviving phase-averaged magnetic field. Pulsed emission is no longer possible, but a substantial flux of unpulsed high-energy photons can be produced. I will present results showing that the physical conditions at the termination shock can be divided into two regimes: a high density one, where current sheets in the wind are first compressed by an MHD shock and subsequently dissipate by reconnection, and a low density one, where the wind can first convert into an electromagnetic wave in the shock precursor, which then damps and merges into the wind nebula. The shocks surrounding isolated pulsars fall into the low-density category, but those around pulsars in binary systems, may transit from one regime to the other according to binary phase. The implications of the shock-structure dichotomy for these objects will be discussed.

scholarly journals Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 yr of ANTARES data

2020 ◽  
Vol 500 (4) ◽  
pp. 5614-5628
Author(s):  
A Albert ◽  
M André ◽  
M Anghinolfi ◽  
G Anton ◽  
M Ardid ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Neutrino Flux ◽  
Radial Distance ◽  
Optimization Procedure ◽  
Lorentz Factor ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Model Parameters ◽  
The Impact ◽  
Astrophysical Neutrino

ABSTRACT Addressing the origin of the astrophysical neutrino flux observed by IceCube is of paramount importance. Gamma-Ray Bursts (GRBs) are among the few astrophysical sources capable of achieving the required energy to contribute to such neutrino flux through pγ interactions. In this work, ANTARES data have been used to search for upward going muon neutrinos in spatial and temporal coincidence with 784 GRBs occurred from 2007 to 2017. For each GRB, the expected neutrino flux has been calculated in the framework of the internal shock model and the impact of the lack of knowledge on the majority of source redshifts and on other intrinsic parameters of the emission mechanism has been quantified. It is found that the model parameters that set the radial distance where shock collisions occur have the largest impact on neutrino flux expectations. In particular, the bulk Lorentz factor of the source ejecta and the minimum variability time-scale are found to contribute significantly to the GRB-neutrino flux uncertainty. For the selected sources, ANTARES data have been analysed by maximizing the discovery probability of the stacking sample through an extended maximum-likelihood strategy. Since no neutrino event passed the quality cuts set by the optimization procedure, 90 per cent confidence level upper limits (with their uncertainty) on the total expected diffuse neutrino flux have been derived, according to the model. The GRB contribution to the observed diffuse astrophysical neutrino flux around 100 TeV is constrained to be less than 10 per cent.

scholarly journals Doppler Boosting Effect on the Jet Radiation of Gamma-Ray Bursts and Active Galactic Nuclei

2016 ◽  
Vol 12 (S324) ◽  
pp. 82-84
Author(s):  
Xiao-Li Huang ◽  
Hai-Ming Zhang ◽  
Shu-Qing Zhong ◽  
En-Wei Liang
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
High Energy ◽  
Mass Scale ◽  
Gamma Ray Bursts ◽  
Radiation Physics ◽  
Physical Laws ◽  
Bl Lacs

AbstractHigh energy photon radiations of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) are dominated by their jet radiations. It was suggested that relativistic jets powered by different mass-scale black holes may share the same physical laws. A tight relation among the peak luminosity, the peak photon energy in the νfν spectrum, and the initial Lorentz factor is found for GRBs. With samples of GeV-TeV BL Lacs, FSRQs, and NLS1 galaxies, we show that these sources do not follow this relation. This may be attributed to the jet geometry and continuous/episodic jet as well as radiation physics for different kinds of sources.

PULSED HIGH-ENERGY EMISSION AND PHASE-RESOLVED SPECTRA BY INVERSE COMPTON SCATTERING IN A PULSAR STRIPED WIND

2008 ◽  
Vol 17 (10) ◽  
pp. 1969-1976
Author(s):  
JÉRÔME PÉTRI ◽  
JOHN G. KIRK
Keyword(s):  
Gamma Ray ◽  
Direct Consequence ◽  
High Energy ◽  
Light Curves ◽  
Inverse Compton Scattering ◽  
Energy Emission ◽  
Inverse Compton ◽  
Pulse Structure ◽  
And Behavior ◽  
High Energy Emission

To date, seven gamma-ray pulsars are known, showing pulsed emission up to tens of GeV and associated light-curves with a double-pulse structure. We study this pulsed high-energy emission in the framework of the striped wind model. By numerical integration of the time-dependent emissivity in the current sheets, we compute the phase-dependent spectral variability of the inverse Compton radiation. Several light curves and spectra are presented. The pulses are a direct consequence of relativistic beaming. Our model is able to explain some of the high-energy (10 MeV–10 GeV) spectral features and behavior of several gamma-ray pulsars, such as Geminga and Vela.

A MODEL FOR THE INNER JET HIGH-ENERGY EMISSION OF CENTAURUS A

2010 ◽  
Vol 19 (06) ◽  
pp. 937-942
Author(s):  
MARIANA ORELLANA ◽  
GUSTAVO E. ROMERO
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Meson Production ◽  
High Energy ◽  
Spectral Energy ◽  
Hadronic Interactions ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Great Relevance ◽  
Centaurus A

We investigate the spectral energy distribution (SED) of Centaurus A resulting from a steady compact acceleration region, located close to the central black hole, where both leptonic and hadronic relativistic populations arise. We present here results of such a model, where we have considered synchrotron radiation by primary electrons and protons, inverse Compton scattering, and gamma-ray emission originated by the inelastic hadronic interactions between relativistic protons and cold nuclei within the jets. Photo-meson production by relativistic hadrons were also taken into account, as well as the effects of secondary particles injected by all interactions. The internal and external absorption of gamma-rays is shown to be of great relevance to shape the observable SED, which was also recently constrained by the results of Fermi and HESS.

scholarly journals Nonthermal emission from high-mass microquasar jets affected by orbital motion

2018 ◽  
Vol 618 ◽  
pp. A146 ◽  
Author(s):  
E. Molina ◽  
V. Bosch-Ramon
Keyword(s):  
Radio Emission ◽  
Stellar Wind ◽  
Gamma Ray ◽  
Orbital Motion ◽  
Source Parameters ◽  
High Energy ◽  
High Mass ◽  
Broadband Emission ◽  
Inverse Compton ◽  
The Impact

Context. The stellar wind in high-mass microquasars should interact with the jet. This interaction, coupled with orbital motion, is expected to make the jet follow a helical, nonballistic trajectory. The jet energy dissipated by this interaction, through shocks for example, could lead to nonthermal activity on scales significantly larger than the system size. Aims. We calculate the broadband emission from a jet affected by the impact of the stellar wind and orbital motion in a high-mass microquasar. Methods. We employ a prescription for the helical trajectory of a jet in a system with a circular orbit. Subsequently, assuming electron acceleration at the onset of the helical jet region, we compute the spatial and energy distribution of these electrons, and their synchrotron and inverse Compton emission including gamma-ray absorption effects. Results. For typical source parameters, significant radio, X- and gamma-ray luminosities are predicted. The scales on which the emission is produced may reduce, but not erase, orbital variability of the inverse Compton emission. The wind and orbital effects on the radio emission morphology could be studied using very long baseline interferometric techniques. Conclusions. We predict significant broadband emission, modulated by orbital motion, from a helical jet in a high-mass microquasar. This emission may be hard to disentangle from radiation of the binary itself, although the light curve features, extended radio emission, and a moderate opacity to very high-energy gamma rays, could help to identify the contribution from an extended (helical) jet region.

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