ACCELERATION OF PARTICLES AT THE TERMINATION SHOCK OF A RELATIVISTIC STRIPED WIND

By L. Sironi, A. Spitkovsky. 2011

213 citations recorded by the source corpus.

The relativistic wind of obliquely rotating pulsars consists of toroidal stripes of opposite magnetic field polarity, separated by current sheets of hot plasma. By means of two- and three-dimensional particle-in-cell simulations, we investigate particle acceleration and magnetic field dissipation at the termination shock of a relativistic striped wind. At the shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength λ or the wind magnetization σ (in the regime σ ≫ 1 of magnetically dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles, whose average Lorentz factor increases by a factor of σ with respect to the pre-shock value. The shape of the post-shock spectrum depends primarily on the ratio λ/(rLσ), where rL is the relativistic Larmor radius in the wind. The spectrum becomes broader as the value of λ/(rLσ) increases, passing from a relativistic Maxwellian to a flat power-law tail with slope around −1.5, populated by particles accelerated by the reconnection electric field. Close to the equatorial plane of the wind, where the stripes are symmetric, the highest energy particles resulting from magnetic reconnection can escape ahead of the shock, and be injected into a Fermi-like acceleration process. In the post-shock spectrum, they populate a power-law tail with slope around −2.5, which extends beyond the flat component produced by reconnection. Our study suggests that the spectral break between the radio and the optical band in Pulsar Wind Nebulae can be a natural consequence of particle acceleration at the termination shock of striped pulsar winds.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. L. Sironi
2. A. Spitkovsky
3. B. Metzger
4. D. Giannios
5. J. Arons
6. M. Petropoulou
7. B. Cerutti
8. Bing Zhang

In Instrumentation

1. D. Giannios
2. L. Sironi
3. B. Metzger
4. J. Arons
5. U. Keshet
6. M. Lemoine
7. M. Petropoulou
8. P. Serpico

Citations in the corpus

• Millisecond Magnetar Birth Connects FRB 121102 to Superluminous Supernovae and Long-duration Gamma-Ray Bursts (2017, background): “…has led to the suggestion of other acceleration sites than the termination shock, such as the magnetic reconnection in the striped pulsar wind (e.g. Sironi & Spitkovsky 2011; Zrake & Arons 2016), which particle-in-cell plasma simulations show can indeed produce flatter (p < 2) electron spec- tra…”
• RELATIVISTIC RECONNECTION: AN EFFICIENT SOURCE OF NON-THERMAL PARTICLES (2014, background): “Yet, no consensus exists whether relativistic reconnection results self-consistently in non-thermal particle acceleration (Sironi & Spitkovsky 2011a), rather than just heating (Cerutti et al. 2012).”
• Gamma-ray binaries and related systems (2013, background): “Simulations of shock-driven reconnection by Sironi & Spitkovsky (2011) find that particles initially accelerated by reconnection in the equatorial plane are further accelerated by a “Fermi-like” process, yielding a power-law spectrum, with the magnetic energy efficiently transferred to the…”
• Three-dimensional magnetohydrodynamic simulations of the Crab nebula (2013, background): “But what is even more important is that the recent advanced particle-in-cell (PIC) simulations show that the acceleration of non-thermal particles does not operate at such shocks (Sironi & Spitkovsky 2009, 2011b).”
• Astrophysical models for the origin of the positron (2011, background): “Yet, recent two- and three-dimensional particle-in-cell simulations seem to support this kind of scenario [85].”
• Relativistic Shocks: Particle Acceleration and Magnetization (2015, methodology): “In contrast, superluminal shocks (θ & θcrit) show negligible particle acceleration (Gallant et al. 1992; Hoshino 2008; Sironi and Spitkovsky 2009a, 2011b; Sironi et al. 2013).”
• THE MAXIMUM ENERGY OF ACCELERATED PARTICLES IN RELATIVISTIC COLLISIONLESS SHOCKS (2013, methodology): “…the conclusion that particle acceleration along extended X-lines formed by tearing of the current sheets may contribute to the flat particle distribution (with spectral index p ' 1.5) required to explain the far infrared and radio spectra of PWNe (e.g., Lyubarsky 2003; Sironi & Spitkovsky 2011a).”
• GAMMA-RAY ACTIVITY IN THE CRAB NEBULA: THE EXCEPTIONAL FLARE OF 2011 APRIL (2011, background): “We note that such a spectrum is also inferred for the radio emitting electrons in the Crab Nebula, and more generally in pulsar wind nebulas (Gaensler & Slane 2006; Sironi & Spitkovsky 2011a).”
• Reconnection-driven plasmoids in blazars: fast flares on a slow envelope (2012, background): “Additional acceleration of particles takes place during the merging process of the plasmoids (Zenitani & Hoshino 2001; 2005; Drake et al. 2006, Sironi & Spitkovsky 2011; although the energy spectrum of the particles depends on the details and is still topic of investigation).”
• SIMULATIONS OF PARTICLE ACCELERATION BEYOND THE CLASSICAL SYNCHROTRON BURNOFF LIMIT IN MAGNETIC RECONNECTION: AN EXPLANATION OF THE CRAB FLARES (2013, background): “It tends to suppress the development of the drift kink instability that occurs only in 3D, which may quench non-thermal particle acceleration (Zenitani & Hoshino 2008, see also the discussion in Liu et al. 2011; Sironi & Spitkovsky 2011; Kagan et al. 2012).”
• Non-thermal particle acceleration in collisionless relativistic electron-proton reconnection (2016, background): “…and pulsar wind nebulae (PWNe) (Coroniti 1990; Lyubarsky & Kirk 2001; Zenitani & Hoshino 2001; Kirk & Skjæraasen 2003; Kirk 2004; Contopoulos 2007a,b; Sironi & Spitkovsky 2011; Uzdensky et al. 2011; Cerutti et al. 2012a,b, 2013, 2014a,b; Uzdensky & Spitkovsky 2014; Philippov & Spitkovsky…”
• A Concordance Picture of FRB 121102 as a Flaring Magnetar Embedded in a Magnetized Ion–Electron Wind Nebula (2018, background): “Although some of the power of a collisionless magnetized shock is transferred into the ions, we assume that the electrons are also efficiently heated, e.g., by small-scale turbulence generated by the ions ahead of the shock (Sironi & Spitkovsky 2011) or other plasma scale processes.”
• Plasmoids in relativistic reconnection, from birth to adulthood: first they grow, then they go (2016, methodology): “…Nalewajko et al. 2015; Sironi et al. 2015; Werner et al. 2016; Kagan et al. 2016) and three dimensions (3D; e.g., Zenitani & Hoshino 2005, 2008; Yin et al. 2008; Liu et al. 2011; Sironi & Spitkovsky 2011a, 2012; Kagan et al. 2013; Cerutti et al. 2013b; Sironi & Spitkovsky 2014; Guo et al. 2015).”