Abstract
Context. According to current pulsar emission models, photons are produced within their magnetosphere and current sheet, along their separatrix, which is located inside and outside the light cylinder. Radio emission is favoured in the vicinity of the polar caps, whereas the high-energy counterpart is presumably enhanced in regions around the light cylinder, whether this is the magnetosphere and/or the wind. However, the gravitational effect on their light curves and spectral properties has only been sparsely researched. Aims. We present a method for simulating the influence that the gravitational field of the neutron star has on its emission properties according to the solution of a rotating dipole evolving in a slowly rotating neutron star metric described by general relativity. Methods. We numerically computed photon trajectories assuming a background Schwarzschild metric, applying our method to neutron star radiation mechanisms such as thermal emission from hot spots and non-thermal magnetospheric emission by curvature radiation. We detail the general-relativistic effects onto observations made by a distant observer. Results. Sky maps are computed using the vacuum electromagnetic field of a general-relativistic rotating dipole, extending previous works obtained for the Deutsch solution. We compare Newtonian results to their general-relativistic counterpart. For magnetospheric emission, we show that aberration and curvature of photon trajectories as well as Shapiro time delay significantly affect the phase delay between radio and high-energy light curves, although the characteristic pulse profile that defines pulsar emission is kept.
Highlights
In 1967, Jocelyn Bell observed a radio source that with extreme regularity displayed an emission peak every 1.337 s
We present a method for simulating the influence that the gravitational field of the neutron star has on its emission properties according to the solution of a rotating dipole evolving in a slowly rotating neutron star metric described by general relativity
We show that aberration and curvature of photon trajectories as well as Shapiro time delay significantly affect the phase delay between radio and high-energy light curves, the characteristic pulse profile that defines pulsar emission is kept
Summary
In 1967, Jocelyn Bell observed a radio source that with extreme regularity displayed an emission peak every 1.337 s. There are currently more than 2000 identified pulsars, and these stellar remnants are known for their typical pulsed radio emission (Lyne & Manchester 1988), the Fermi large area telescope (Fermi/LAT) confirmed the existence of pulsation in the gamma-ray domain (Abdo et al 2013) for more than 250 of these pulsars This gamma-ray activity gives us an insight into the pulsar magnetosphere, especially into where the emission sites for high-energy emission are located, because they must be well above the polar cap in order to avoid too strong magnetic photon absorption in the magnetic field close to the critical value of 4.4 × 109 T (Daugherty & Harding 1996).
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