Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet’s Tale
By J. Arons. Space Science Reviews, 2012
136 citations recorded by the source corpus.
I outline, from a theoretical and somewhat personal perspective, significant features of Pulsar Wind Nebulae (PWNe) as Cosmic Accelerators. I pay special attention to the recently discovered gamma ray “flares” in the Crab Nebula’s emission, focusing on the possibility, raised by the observations, that the accelerating electric field exceeds the magnetic field, suggesting that reconnection in the persistent current layer (a “current sheet”) plays a significant role in the behavior of this well studied Pevatron. I address the present status of the termination shock model for the particle accelerator that converts the wind flow energy to the observed non-thermal particle spectra, concluding that it has a number of major difficulties related to the transverse magnetic geometry of the shock wave. I discuss recent work on the inferred pair outflow rates, which are in excess of those predicted by existing theories of pair creation, and use those results to point out that the consequent mass loading of the wind reduces the wind’s bulk flow 4-velocity to the point that dissipation of the magnetic field in a pulsar’s wind upstream of the termination shock is restored to life as a viable model for the solution of the “σ” problem. I discuss some suggestions that current starvation in the current flow supporting the structured (“striped”) upstream magnetic field perhaps induces a transition to superluminal wave propagation. I show that current starvation probably does not occur, because those currents are carried in the current sheet separating the stripes rather than in the stripes themselves.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/0fbe68d860a07e30f2a97b90e33d88b3ce15baab
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Citations in the corpus
- PARTICLE ACCELERATION AND PLASMA DYNAMICS DURING MAGNETIC RECONNECTION IN THE MAGNETICALLY DOMINATED REGIME (2015, background): “…is often invoked to explain high-energy emissions and ultra-high-energy cosmic rays from objects such as pulsar wind nebulae (PWNe; Kirk 2004; Arons 2012; Uzdensky & Spitkovsky 2014), jets from active galactic nuclei (AGN; de Gouveia dal Pino & Lazarian 2005; Giannios et al. 2009), and…”
- Ab-initio Pulsar Magnetosphere: Particle Acceleration in Oblique Rotators and High-energy Emission Modeling (2017, background): “This is important for reaching ex- tremely high energies, since ion acceleration in the return current layer at the boundary of closed field line region becomes limited due to curvature radiation losses (Arons 2012).”
- Particle acceleration in axisymmetric pulsar current sheets (2014, background): “The precipitation of the energetic electrons onto the star may be an additional source of radiation, an “auroral”-like emission (Arons 2012).”
- Three-dimensional magnetohydrodynamic simulations of the Crab nebula (2013, background): “…dissipation length scale still significantly exceeds the radius of the wind termination shock (Lyubarsky & Kirk 2001), unless the pulsar produces much more plasma compared to the predictions of the current models of pair-production in pulsar magnetospheres (see Arons 2012, and references therein).”
- Relativistic Shocks: Particle Acceleration and Magnetization (2015, background): “Another “external” influence of reconnection on the shock structure, that might lead to particle acceleration to higher energies, may be connected to the accelerator behind the recently discovered gamma-ray flares in the Crab Nebula (Abdo 2011).”