A novel approach for the analysis of the geometry involved in determining light curves of pulsars

Abstract

In this work, we introduce the use of the differential geometry Frenet-Serret equations to describe a magnetic line in a pulsar magnetosphere. These equations, which need to be solved numerically, fix the magnetic line in terms of their tangent, normal, and binormal vectors at each position, given assumptions on the radius of curvature and torsion. Once the representation of the magnetic line is defined, we provide the relevant set of transformations between reference frames; the ultimate aim is to express the map of the emission directions in the star co-rotating frame. In this frame, an emission map can be directly read as a light curve seen by observers located at a certain fixed angle with respect to the rotational axis. We provide a detailed step-by-step numerical recipe to obtain the emission map for a given emission process, and give a set of simplified benchmark tests. Key to our approach is that it offers a setting to achieve an effective description of the system's geometry together with the radiation spectrum. This allows to compute multi-frequency light curves produced by a specific radiation process (and not just geometry) in the pulsar magnetosphere, and intimately relates with averaged observables such as the spectral energy distribution.

Exploring the energy-dependent radiation properties in dissipative magnetospheres with Fermi pulsars

“…The expression of the curvature radius used in the paper is essentially the same as the one given by , but different forms. Recently, similar approach to determine the curvature radius is also performed by introducing the differential geometry Frenet-Serret equations to express the trajectories of the particles by Viganò & Torres (2020) . The equilibrium γ L values balanced by the acceleration of E || and the CR loss can be obtained in the equilibrium of radiative reaction region (dγ/dt = 0)by…”