Relativistic Shocks: Particle Acceleration and Magnetization

By L. Sironi, U. Keshet, M. Lemoine. 2015

181 citations recorded by the source corpus.

We review the physics of relativistic shocks, which are often invoked as the sources of non-thermal particles in pulsar wind nebulae (PWNe), gamma-ray bursts (GRBs), and active galactic nuclei (AGN) jets, and as possible sources of ultra-high energy cosmic-rays. We focus on particle acceleration and magnetic field generation, and describe the recent progress in the field driven by theory advances and by the rapid development of particle-in-cell (PIC) simulations. In weakly magnetized or quasi parallel-shocks (i.e. where the magnetic field is nearly aligned with the flow), particle acceleration is efficient. The accelerated particles stream ahead of the shock, where they generate strong magnetic waves which in turn scatter the particles back and forth across the shock, mediating their acceleration. In contrast, in strongly magnetized quasi-perpendicular shocks, the efficiencies of both particle acceleration and magnetic field generation are suppressed. Particle acceleration, when efficient, modifies the turbulence around the shock on a long time scale, and the accelerated particles have a characteristic energy spectral index of sγ≃2.2$s_{\gamma}\simeq2.2$ in the ultra-relativistic limit. We discuss how this novel understanding of particle acceleration and magnetic field generation in relativistic shocks can be applied to high-energy astrophysical phenomena, with an emphasis on PWNe and GRB afterglows.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/cf274557e9779cc5b5764fae7f43b1f241ae0df2

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In Astronomy and Astrophysics

1. B. Metzger
2. Bing Zhang
3. E. Berger
4. Pawan Kumar
5. B. Margalit
6. W. Fong
7. Raffaella Margutti
8. Ryan Chornock

In Nuclear and High Energy Physics

1. E. Berger
2. Bing Zhang
3. F. Tavecchio
4. B. Metzger
5. Pawan Kumar
6. L. Maraschi
7. G. Bonnoli
8. B. Margalit

Citations in the corpus

• A unified picture of Galactic and cosmological fast radio bursts (2020, background): “Simulations suggest that shocks in a magnetized pair plasma might not produce an extended power-law particle spectrum above the average energy per particle (Sironi et al. 2015), i.e., little emission above νm.”
• The Blazar TXS 0506+056 Associated with a High-energy Neutrino: Insights into Extragalactic Jets and Cosmic-Ray Acceleration (2018, background): “Various mechanisms have been proposed for accelerating UHECRs in AGN jets, involving strong shocks, magnetic reconnection, shear flows, etc. (Bykov et al. 2012; Sironi et al. 2015).”
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. V. Rising X-Ray Emission from an Off-axis Jet (2017, methodology): “…(median value from short GRBs afterglows from Fong et al. 2015) and =p 2.2 (as expected from particle acceleration in the ultra-relativistic limit; Sironi et al. 2015), and we run each simulation for a collimated q = 5j jet and a jet with q = 15j , representative of a less collimated outflow…”
• An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients (2018, background): “In addition to accelerating electrons into a nonthermal distribution, the forward shock is also predicted to heat electrons (Sironi et al. 2015), generating a relativistic Maxwellian particle distribution with a mean thermal Lorentz factor, f m m v c f v 2 4.6 0.5 , 18e p e eth sh 2 0.1 2g » »⎜ ⎟ ⎛…”