Dissipation in pulsar winds

Abstract

I review the constraints placed on relativistic pulsar winds by comparing optical and X-ray images of the inner Crab Nebula on the one hand with two-dimensional MHD simulations on the other. The various proposals in the literature for achieving the low magnetisation required at the inner edge of the Nebula, are then discussed, emphasising that of dissipation in the striped-wind picture. The possibility of direct observation of the wind is examined. Based on the predicted orientation of the polarisation vector, I outline a new argument suggesting that the off-pulse component of the optical emission of the Crab pulsar originates in the wind.

Investigating the origin of optical and X-ray pulsations of the transitional millisecond pulsar PSR J1023+0038

“…A geometric factor < 1 indicates that the pulsar wind is concentrated on the equatorial plane, as also suggested by several models of the Crab pulsar (see, e.g., Kirk 2006).…”

The Dawes Review 11: From young to old: The evolutionary path of Pulsar Wind Nebulae

“…One of the longer standing problems in PWNe physics, the so called sigma-paradox (Melatos 1998), arose as consequence of these 1D models, and puzzled the community for more than thirty years: in order to explain the existence of the TS, the average magnetisation in the nebula must be quite low: (Kennel & Coroniti 1984b). But theoretical models of pulsar magnetospheres predict a much larger magnetisation at the light cylinder of the star: (Kirk et al 2009; Arons 2012). To make compatible these two opposite predictions, a huge amount of magnetic dissipation must be considered along the path separating the light cylinder and the pulsar wind termination shock, converting the pulsar wind from a Poynting dominated outflow to a particle dominated one.…”

“…Moreover the presence of a bright source makes IC a relatively strong cooling process, to the point that it is unclear if the observed X-ray emission is synchrotron or IC (Neronov & Chernyakova, 2007;Kargaltsev et al, 2014;Bednarek & Sitarek, 2013;Zdziarski et al, 2010;Paredes-Fortuny et al, 2015;Bosch-Ramon et al, 2012). These systems offer us a unique opportunity to investigate the PSR wind and its acceleration properties, at distances much smaller than in regular PWNe, and can have important consequences on a large set of dissipative wind models (Kirk & Skjaeraasen, 2003;Kirk, 2006;Lyubarsky, 2010;Takamoto et al, 2012;Cerutti & Philippov, 2017;Cerutti et al, 2020;Huber et al, 2021a,b).…”

“…As in normal bow-shocks, particles can be accelerated to high energy, but unlike regular systems, the orbital dynamics can lead to a substantial mixing with the stellar material, a high level of turbulence, and the development of multiple shocks, with distributed acceleration. Moreover the presence of a bright source makes IC a relatively strong cooling process, to the point that it is unclear if the observed X-ray emission is synchrotron or IC (Neronov & Chernyakova 2007;Kargaltsev et al 2014;Bednarek & Sitarek 2013;Zdziarski, Neronov, & Chernyakova 2010;Paredes-Fortuny et al 2015;Bosch-Ramon et al 2012) These systems offer us a unique opportunity to investigate the PSR wind and its acceleration properties, at distances much smaller than in regular PWNe, and can have important consequences on a large set of dissipative wind models (Kirk & Skjaeraasen 2003;Kirk 2006;Lyubarsky 2010;Takamoto, Inoue, & Inutsuka 2012;Cerutti & Philippov 2017;Cerutti, Philippov, & Dubus 2020;Huber et al 2021a;Huber, Kissmann, & Reimer 2021b).…”

Pulsar wind zone processes in LS 5039

“…On one hand, the magnetization parameter may be a function of angle, and although must be very small in the equatorial part of the wind e.g., [46], simulations do not favor an angle-independent low value [50]. On the other hand, Contopoulos and Kazanas [29] already showed that the Lorentz factor of the outflowing plasma could increase linearly with distance from the light cylinder (implying that r decreases inversely proportional to the distance).…”