Particle Acceleration in Astrophysical Shear Flows

Rieger, F.; Duffy, P.

doi:10.1088/1009-9271/5/s1/195

Cited by 9 publications

(12 citation statements)

References 35 publications

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“…Particle acceleration in shear flows has been previously investigated by many authors, mainly related to astrophysical scenarios (Berezhko and Krymskii 1981, Jopikii and Morfill 1990, Ostrowski 1990, Rieger and Duffy 2005, Rieger and Mannheim 2002, Webb 1989). The shear acceleration mechanism (Rieger and Duffy 2005) is based on the idea that energetic particles may gain energy by systematically scattering off moving small-scale magnetic field irregularities. These irregularities are thought to be embedded in a collisionless shear flow such that their velocities correspond to the local flow velocity.…”

Section: Particle Accelerationmentioning

confidence: 99%

Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets

Alves¹,

Grismayer²,

Fonseca

et al. 2014

New J. Phys.

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Strong shear flow regions found in astrophysical jets are shown to be important dissipation regions, where the shear flow kinetic energy flow is converted into electric and magnetic field energy via shear instabilities. The emergence of these self-consistent fields makes shear flows significant sites for radiation emission and particle acceleration. We focus on electron-scale instabilities, namely the collisionless, unmagnetized electron-scale Kelvin-Helmholtz instability (ESKHI) and a large-scale DC magnetic field generation mechanism on the electron scales. We show that these processes are important candidates to generate magnetic fields in the presence of strong velocity shears, which may naturally originate in energetic matter outbursts of active galactic nuclei and gamma-ray bursters. We show that the ESKHI is robust to density jumps between shearing flows, thus operating in various scenarios with different density contrasts. Multidimensional particle-incell (PIC) simulations of the ESKHI, performed with OSIRIS, reveal the emergence of a strong and large-scale DC magnetic field component, which is not captured by the standard linear fluid theory. This DC component arises from kinetic effects associated with the thermal expansion of electrons of one flow into the other across the shear layer, whilst ions remain unperturbed due to their inertia. The electron expansion forms DC current sheets, which induce a DC magnetic field. Our results indicate that most of the electromagnetic energy Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. developed in the ESKHI is stored in the DC component, reaching values of equipartition on the order of − 10 3 in the electron time-scale, and persists longer than the proton time-scale. Particle scattering/acceleration in the self-generated fields of these shear flow instabilities is also analyzed. New J. Phys. 16 (2014) 035007 E P Alves et al New J. Phys. 16 (2014) 035007 E P Alves et al New J. Phys. 16 (2014) 035007 E P Alves et al 4 New J. Phys. 16 (2014) 035007 E P Alves et al 5 New J. Phys. 16 (2014) 035007 E P Alves et al 6 New J. Phys. 16 (2014) 035007 E P Alves et al 7 Figure 2. Simplified theoretical setting: tangential discontinuity velocity shear between different uniform density flows. New J. Phys. 16 (2014) 035007 E P Alves et al 8 New J. Phys. 16 (2014) 035007 E P Alves et al 9 New J. Phys. 16 (2014) 035007 E P Alves et al 24

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Section: Particle Accelerationmentioning

confidence: 99%

Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets

Alves¹,

Grismayer²,

Fonseca

et al. 2014

New J. Phys.

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“…[59], [60] and [61], respectively; see also [40]). Fermi I mechanism could take place due to internal shocks in the jet; Fermi II acceleration could take place if magnetic turbulence is significant enough; shear layer would be a natural outcome of an expanding jet or different jet/medium velocities.…”

Section: The Binary System Scalesmentioning

confidence: 90%

“…The highest energy particle is derived from the acceleration efficiencies in balance with the radiative losses and the accelerator size, leading to GeV energies for electrons in the jet innermost regions and >TeV elsewhere; protons are not cooling restricted, being able to reach >TeV everywhere in the jet (see e.g. [40]). The adopted acceleration efficiency allows for instance to reach TeV photon production energies for the emitting particles.…”

Section: Studying High Energy Emission In the Mq Scenariomentioning

confidence: 99%

“…Regarding particle acceleration, although internal shocks may take place still at these distances from the compact object associated perhaps with violent episodes occurring in the jet base, Fermi II type and shear acceleration appear more plausible for a continuous outflow at these scales (something similar could happen in the intra-knot regions of extragalactic jets, see, e.g., [40]). …”

Section: The Jet Middle Scalesmentioning

confidence: 99%

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Theoretical overview on high-energy emission in microquasars

Bosch‐Ramon

2007

The Multi-Messenger Approach to High-Energy Gamma-Ray Sources

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Microquasar (MQ) jets are sites of particle acceleration and synchrotron emission. Such synchrotron radiation has been detected coming from jet regions of different spatial scales, which for the instruments at work nowadays appear as compact radio cores, slightly resolved radio jets, or (very) extended structures (e.g.Because of the presence of relativistic particles and dense photon, magnetic and matter fields, these outflows are also the best candidates to generate the very high-energy (VHE) gamma-rays detected coming from two of these objects, LS 5039 and LS I +61 303 ([4,5], and [6], respectively), and may be contributing significantly to the X-rays emitted from the MQ core (e.g. [7], [8]). In addition, beside electromagnetic radiation, jets at different scales are producing some amount of leptonic and hadronic cosmic rays (CR), and evidences of neutrino production in these objects may be eventually found. In this work, we review on the different physical processes that may be at work in or related to MQ jets. The jet regions capable to produce significant amounts of emission at different wavelengths have been reduced to the jet base, the jet at scales of the order of the size of the system orbital semi-major axis, the jet middle scales (the resolved radio jets), and the jet termination point. The surroundings of the jet could be sites of multiwavelegnth emission as well, deserving also an insight. We focus on those scenarios, either hadronic or leptonic, in which it seems more plausible to generate both photons from radio to VHE and high-energy neutrinos. We briefly comment as well on the relevance of MQ as possible contributors to the galactic CR in the GeV-PeV range.

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“…This happens more efficiently because protons suffer less synchrotron losses than electrons. At the same time, protons have a higher gyro radius r gy ∝ E/B, which is proportional to the mean scattering time [Rie05]. The low energy hump is explained by synchrotron radiation of co-accelerated electrons.…”

Section: Hadronic Modelsmentioning

confidence: 99%

Measurement of Very High Energy Gamma‐Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study

Wagner¹

2007

PUBL ASTRON SOC PAC

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SummaryThe thesis reports on the measurement of very high energy (VHE) gamma-rays from four Active Galactic Nuclei (AGN) with the Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC). When taking into account -ray absorption by the extragalactic background light (EBL), a hint for an inverse Compton peak is found with the peak energy moving from (0.3 ± 0.1) TeV to (1.4 ± 0.7) TeV with increasing flux level. This evidence is strengthened by the observation of a moving structure also in the measured spectra, which are free of uncertainties of the EBL model used.Unprecedented rapid flux variability with doubling times of ≤ 5 minutes was found during some of the observation nights. These fast flares are used to infer significant limits on the size of the acceleration region of R · δ −1 ≤ 10 12 cm for homogeneous one-zone SelfSynchrotron Compton models. Significant spectral hardening of ∆α = 0.4 within less than 20 minutes could be observed. The well-defined fast flares were also used to infer a lower limit on the quantum gravity energy scale of 1.5 × 10 17 GeV.For the BL Lac object 1ES 2344+514 for the first time a differential energy spectrum during a state of low -ray activity is inferred, which between 140 GeV and 5 TeV can be vii described by a power law of the form dF dE = (1.18 ± 0.13) × 10The study of the 24-day VHE -ray light curve of 1ES 2344+514 yields a low flux level of 0.04 ≤ F E>350 GeV ≤ 0.11 times the Crab nebula flux. In combination with the all-time (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)) light curve a low emission level of about ≈4% of the Crab nebula flux is found.Within the thesis, predictions for the detectability of BL Lac candidate objects in VHE -rays with the MAGIC telescope are presented. These predictions led to the discovery of two new objects in this energy domain, PG 1553+113 and BL Lacertae. PG 1553+113 was detected at a high significance level of 8.8σ . The softest gamma ray spectrum observed so far in VHE -rays was found for this source. It can be described by a pure power law between 95 GeV and 500 GeV:The spectrum is used to infer an upper limit of z < 0.78 on the yet undetermined redshift of PG 1553+113 by imposing a maximum hardness of the intrinsic spectrum. While the light curve does not show apparent short-term variability, simultaneously recorded optical data feature a substantial flare, which leaves room for interpretation of the non-existing correlations.BL Lacertae, the prototype of the BL Lac objects, was detected at a significance level of 5.6σ . This object is the first low-frequency peaked BL Lac object seen in VHE -rays. A preliminary spectrum hints at a steep slope of ≈ −3.7 between 100 GeV and 1 TeV.For the first time a synoptic study of all high-frequency peaked BL Lac-type objects detected as VHE gamma-ray emitters is performed. The intrinsic properties of the observed emission are compared and correlated among each other and with the individual estimated black hole masses. Key findings are (1) that all currently known VHE -r...

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Particle Acceleration in Astrophysical Shear Flows

Cited by 9 publications

References 35 publications

Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets

Electron-scale shear instabilities: magnetic field generation and particle acceleration in astrophysical jets

Theoretical overview on high-energy emission in microquasars

Measurement of Very High Energy Gamma‐Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study

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