Expositor: Daniel Íñiguez Pascual (Institut de Ciències de l’Espai (ICE-CSIC), Barcelona)
Fecha: viernes 11 de septiembre, 11:30 hs.
Resumen: Pulsars are rapidly rotating neutron stars with very short spin periods and strong magnetic fields. Typically detected by their radio emission, a percentage of them also emit high-energy radiation. Some relevant aspects of this emission are still not perfectly understood, such as the radiation mechanism at work or the place of production. In this seminar I will present a project focused on understanding this high-energy emission using effective radiative and geometrical models. These models are then compared with observational data in order to obtain conclusions about the high-energy emission of pulsars.
The radiative model solves the dynamics of magnetospheric charged particles and computes their emission via synchro-curvature radiation. In this way, by varying only three of the model parameters we generate high-energy spectra that are compared with observational ones. The model successfully reproduces the gamma-ray spectra of the whole population of pulsars, and the whole high-energy spectra, from X-rays to gamma-rays, of those pulsars observed in both bands. This achievement reinforces the idea that synchro-curvature radiation is the mechanism responsible of the high-energy emission of pulsars. Complementary to the radiative model, a spectro-geometrical model addresses the spatial distribution of the high-energy emission of pulsars. Together with the dynamics and radiation of the particles, we also calculate the geometry of their trajectories. With this and a realistic prescription of the shape of the emission region, we produce emission maps, which contain geometrical and spectral information. From these maps we extract light curves, which ultimately depend on two geometrical parameters, and we compare these synthetic light curves with observational ones. We are able to match the global structure of many light curves, reproducing their most relevant features. However, the model is not able to capture small scale features and struggles to resemble very complex or asymmetric light curves. The relative success in this fitting suggests that some of the assumptions taken in the model, such as the location of the emission region and its shape, may broadly reflect the true geometry of the magnetosphere, but indicates that further modelling is required to reproduce all the complexity the observational light curves have. Finally, we explore the origin of the dispersion seen in the observational gamma-ray efficiency of pulsars, which we use to estimate the distribution of the intrinsic efficiency of the mechanism producing the gamma-ray emission.
