Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. II. Connection with γ-Rays

Abstract It is commonly believed that blazar jets are relativistic magnetized plasma outflows from supermassive black holes. One key question is how the jets dissipate magnetic energy to accelerate particles and drive powerful multiwavelength flares. Relativistic magnetic reconnection has been proposed as the primary plasma physical process in the blazar emission region. Recent numerical simulations have shown strong acceleration of nonthermal particles that may lead to multiwavelength flares. Nevertheless, previous works have not directly evaluated γ-ray signatures from first-principles simulations. In this paper, we employ combined particle-in-cell and polarized radiation transfer simulations to study multiwavelength radiation and optical polarization signatures under the leptonic scenario from relativistic magnetic reconnection. We find harder-when-brighter trends in optical and Fermi-LAT γ-ray bands as well as closely correlated optical and γ-ray flares. The swings in optical polarization angle are also accompanied by γ-ray flares with trivial time delays. Intriguingly, we find highly variable synchrotron self-Compton signatures due to inhomogeneous particle distributions during plasmoid mergers. This feature may result in fast γ-ray flares or orphan γ-ray flares under the leptonic scenario, complementary to the frequently considered minijet scenario. It may also imply neutrino emission with low secondary synchrotron flux under the hadronic scenario, if plasmoid mergers can accelerate protons to very high energy.

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Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832624 ◽

2018 ◽

Vol 617 ◽

pp. A30 ◽

Cited By ~ 3

Author(s):

◽

M. L. Ahnen ◽

S. Ansoldi ◽

L. A. Antonelli ◽

C. Arcaro ◽

...

Keyword(s):

Light Curve ◽

Spectral Energy Distribution ◽

Low Frequency ◽

High Energy ◽

Spectral Energy ◽

Polarization Angle ◽

Optical Polarization ◽

Bl Lac Objects ◽

Very High Energy ◽

Very High

Aims. The very high energy (VHE ≳100 GeV) γ-ray MAGIC observations of the blazar S4 0954+65, were triggered by an exceptionally high flux state of emission in the optical. This blazar has a disputed redshift of z = 0.368 or z ≥ 0.45 and an uncertain classification among blazar subclasses. The exceptional source state described here makes for an excellent opportunity to understand physical processes in the jet of S4 0954+65 and thus contribute to its classification. Methods. We investigated the multiwavelength (MWL) light curve and spectral energy distribution (SED) of the S4 0954+65 blazar during an enhanced state in February 2015 and have put it in context with possible emission scenarios. We collected photometric data in radio, optical, X-ray, and γ-ray. We studied both the optical polarization and the inner parsec-scale jet behavior with 43 GHz data. Results. Observations with the MAGIC telescopes led to the first detection of S4 0954+65 at VHE. Simultaneous data with Fermi-LAT at high energy γ-ray (HE, 100 MeV < E < 100 GeV) also show a period of increased activity. Imaging at 43 GHz reveals the emergence of a new feature in the radio jet in coincidence with the VHE flare. Simultaneous monitoring of the optical polarization angle reveals a rotation of approximately 100°. Conclusions. The high emission state during the flare allows us to compile the simultaneous broadband SED and to characterize it in the scope of blazar jet emission models. The broadband spectrum can be modeled with an emission mechanism commonly invoked for flat spectrum radio quasars (FSRQs), that is, inverse Compton scattering on an external soft photon fieldfrom the dust torus, also known as external Compton. The light curve and SED phenomenology is consistent with an interpretation of a blob propagating through a helical structured magnetic field and eventually crossing a standing shock in the jet, a scenario typically applied to FSRQs and low-frequency peaked BL Lac objects (LBL).

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Detection of very-high-energy γ-ray emission from the colliding wind binary η Car with H.E.S.S.

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936761 ◽

2020 ◽

Vol 635 ◽

pp. A167 ◽

Cited By ~ 2

Author(s):

◽

H. Abdalla ◽

R. Adam ◽

F. Aharonian ◽

F. Ait Benkhali ◽

...

Keyword(s):

Binary Systems ◽

High Energy ◽

Emission Region ◽

Reconstructed Signal ◽

Additional Noise ◽

Before And After ◽

Orbital Phase ◽

Very High Energy ◽

Stereoscopic System ◽

Very High

Aims. Colliding wind binary systems have long been suspected to be high-energy (HE; 100 MeV < E < 100 GeV) γ-ray emitters. η Car is the most prominent member of this object class and is confirmed to emit phase-locked HE γ rays from hundreds of MeV to ~100 GeV energies. This work aims to search for and characterise the very-high-energy (VHE; E >100 GeV) γ-ray emission from η Car around the last periastron passage in 2014 with the ground-based High Energy Stereoscopic System (H.E.S.S.). Methods. The region around η Car was observed with H.E.S.S. between orbital phase p = 0.78−1.10, with a closer sampling at p ≈ 0.95 and p ≈ 1.10 (assuming a period of 2023 days). Optimised hardware settings as well as adjustments to the data reduction, reconstruction, and signal selection were needed to suppress and take into account the strong, extended, and inhomogeneous night sky background (NSB) in the η Car field of view. Tailored run-wise Monte-Carlo simulations (RWS) were required to accurately treat the additional noise from NSB photons in the instrument response functions. Results. H.E.S.S. detected VHE γ-ray emission from the direction of η Car shortly before and after the minimum in the X-ray light-curve close to periastron. Using the point spread function provided by RWS, the reconstructed signal is point-like and the spectrum is best described by a power law. The overall flux and spectral index in VHE γ rays agree within statistical and systematic errors before and after periastron. The γ-ray spectrum extends up to at least ~400 GeV. This implies a maximum magnetic field in a leptonic scenario in the emission region of 0.5 Gauss. No indication for phase-locked flux variations is detected in the H.E.S.S. data.

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Studying particle acceleration from driven magnetic reconnection at the termination shock of a relativistic striped wind using particle-in-cell simulations

EPJ Web of Conferences ◽

10.1051/epjconf/202023507003 ◽

2020 ◽

Vol 235 ◽

pp. 07003

Author(s):

Yingchao Lu ◽

Fan Guo ◽

Patrick Kilian ◽

Hui Li ◽

Chengkun Huang ◽

...

Keyword(s):

Particle Acceleration ◽

Magnetic Reconnection ◽

Magnetic Energy ◽

Maximum Energy ◽

Termination Shock ◽

Particle In Cell ◽

Poynting Flux ◽

Electrons And Positrons ◽

Particle Kinetic Energy ◽

Fermi Type

A rotating pulsar creates a surrounding pulsar wind nebula (PWN) by steadily releasing an energetic wind into the interior of the expanding shockwave of supernova remnant or interstellar medium. At the termination shock of a PWN, the Poynting-flux- dominated relativistic striped wind is compressed. Magnetic reconnection is driven by the compression and converts magnetic energy into particle kinetic energy and accelerating particles to high energies. We carrying out particle-in-cell (PIC) simulations to study the shock structure as well as the energy conversion and particle acceleration mechanism. By analyzing particle trajectories, we find that many particles are accelerated by Fermi-type mechanism. The maximum energy for electrons and positrons can reach hundreds of TeV.

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Very High Energy Gamma Rays from Plerions: CANGAROO Results

Symposium - International Astronomical Union ◽

10.1017/s0074180900114597 ◽

1998 ◽

Vol 188 ◽

pp. 125-128

Author(s):

T. Kifune

Keyword(s):

Gamma Rays ◽

Gamma Ray ◽

High Energy ◽

Current Status ◽

Emission Region ◽

Thermal Processes ◽

High Energy Gamma ◽

Very High Energy ◽

Energy Gamma ◽

Very High

The current status of very high energy gamma ray astronomy (in ~ 1 TeV region) is described by using as example results of CANGAROO (Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback). Gamma rays at TeV energies, emitted through inverse Compton effect of electrons or π0 decay from proton interaction, provide direct evidence on “hot” non-thermal processes of the Universe, as well as environmental features, such as the strength of magnetic field in the emission region, for the non-thermal processes.

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Neutrino and γ-ray Emission from the Core of NGC1275 by Magnetic Reconnection: GRMHD Simulations and Radiative Transfer/Particle Calculations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318007950 ◽

2018 ◽

Vol 14 (S342) ◽

pp. 184-188

Author(s):

J. C. Rodríguez-Ramírez ◽

Elisabete M. de Gouveia Dal Pino ◽

R. Alves Batista

Keyword(s):

Monte Carlo ◽

Radiative Transfer ◽

Magnetic Reconnection ◽

Neutrino Flux ◽

Cosmic Ray ◽

High Energy ◽

Emission Model ◽

The Core ◽

Very High Energy ◽

General Relativistic

AbstractVery high energy (VHE) emission has been detected from the radio galaxy NGC1275, establishing it as a potential cosmic-ray (CR) accelerator and a high energy neutrino source. We here study neutrino and γ-ray emission from the core of NGC1275 simulating the interactions of CRs assumed to be accelerated by magnetic reconnection, with the accreting plasma environment. To do this, we combine (i) numerical general relativistic (GR) magneto-hydrodynamics (MHD), (ii) Monte Carlo GR leptonic radiative transfer and, (iii) Monte Carlo interaction of CRs. A leptonic emission model that reproduces the SED in the [103-1010.5] eV energy range is used as the background target for photo-pion interactions+electromagnetic cascading. CRs injected with the power-law index Îº=1.3 produce an emission profile that matches the VHE tail of NGC1275. The associated neutrino flux, below the IceCube limits, peaks at ∼PeV energies. However, coming from a single source, this neutrino flux may be an over-estimation.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2346 ◽

2020 ◽

Vol 498 (1) ◽

pp. 799-820 ◽

Cited By ~ 1

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.

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Large-scale particle acceleration during magnetic reconnection in solar flares

10.5194/egusphere-egu2020-1959 ◽

2020 ◽

Author(s):

Xiaocan Li ◽

Fan Guo

Keyword(s):

Particle Acceleration ◽

Magnetic Reconnection ◽

Power Law ◽

Solar Flares ◽

Large Scale ◽

Magnetic Energy ◽

High Energy ◽

Macroscopic Model ◽

Scale Particle ◽

Reconnection Layer

<p>Magnetic reconnection is a primary driver of magnetic energy release and particle acceleration processes in space and astrophysical plasmas. Solar flares are a great example where observations have suggested that a large fraction of magnetic energy is converted into nonthermal particles and radiation. One of the major unsolved problems in reconnection studies is nonthermal particle acceleration. In the past decade or two, 2D kinetic simulations have been widely used and have identified several acceleration mechanisms in reconnection. Recent 3D simulations have shown that the reconnection layer naturally generates magnetic turbulence. Here we report our recent progresses in building a macroscopic model that includes these physics for explaining particle acceleration during solar flares. We show that, for sufficient large systems, high-energy particle acceleration processes can be well described as flow compression and shear. By means of 3D kinetic simulations, we found that the self-generated turbulence is essential for the formation of power-law electron energy spectrum in non-relativistic reconnection. Based on these results, we then proceed to solve an energetic particle transport equation in a compressible reconnection layer provided by high-Lundquist-number MHD simulations. Due to the compression effect, particles are accelerated to high energies and develop power-law energy distributions. The power-law index and maximum energy are both comparable to solar flare observations. This study clarifies the nature of particle acceleration in large-scale reconnection sites and initializes a framework for studying large-scale particle acceleration during solar flares.</p>

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Fast magnetic energy dissipation in relativistic plasma induced by high order laser modes

High Power Laser Science and Engineering ◽

10.1017/hpl.2016.16 ◽

2016 ◽

Vol 4 ◽

Cited By ~ 7

Author(s):

Y. J. Gu ◽

Q. Yu ◽

O. Klimo ◽

T. Zh. Esirkepov ◽

S. V. Bulanov ◽

...

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Magnetic Energy ◽

Collisionless Plasma ◽

High Energy ◽

Field Energy ◽

Displacement Current ◽

Particle In Cell ◽

Magnetic Field Energy ◽

High Energy Electrons

Fast magnetic field annihilation in a collisionless plasma is induced by using TEM(1,0) laser pulse. The magnetic quadrupole structure formation, expansion and annihilation stages are demonstrated with 2.5-dimensional particle-in-cell simulations. The magnetic field energy is converted to the electric field and accelerate the particles inside the annihilation plane. A bunch of high energy electrons moving backwards is detected in the current sheet. The strong displacement current is the dominant contribution which induces the longitudinal inductive electric field.

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Locating the gamma-ray emission region in the brightest Fermi-LAT flat-spectrum radio quasars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3483 ◽

2020 ◽

Vol 500 (4) ◽

pp. 5297-5321

Author(s):

Atreya Acharyya ◽

Paula M Chadwick ◽

Anthony M Brown

Keyword(s):

Time Scales ◽

Gamma Ray ◽

High Energy ◽

Emission Region ◽

Large Area ◽

Line Region ◽

Spectrum Radio ◽

Show Evidence ◽

Very High Energy ◽

Gamma Ray Emission

ABSTRACT We present a temporal and spectral analysis of the gamma-ray flux from nine of the brightest flat-spectrum radio quasars (FSRQs) detected with the Fermi Large Area Telescope during its first 8 yr of operation, with the aim of constraining the location of the emission region. Using the increased photon statistics obtained from the two brightest flares of each source, we find evidence of sub-hour variability from B2 1520+31, PKS 1502+106, and PKS 1424−41, with the remaining sources showing variability on time-scales of a few hours. These indicate gamma-ray emission from extremely compact regions in the jet, potentially compatible with emission from within the broad-line region (BLR). The flare spectra show evidence of a spectral cut-off in 7 of the 18 flares studied, further supporting the argument for BLR emission in these sources. An investigation into the energy dependence of cooling time-scales finds evidence for both BLR origin and emission from within the molecular torus (MT). However, Monte Carlo simulations show that the very high energy (Eγ ≥ 20 GeV) emission from all sources except 3C 279, 3C 454.3, and 4C 21.35 is incompatible with a BLR origin. The combined findings of all the approaches used suggest that the gamma-ray emission in the brightest FSRQs originates in multiple compact emission regions throughout the jet, within both the BLR and the MT.

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