High-energy pulses and phase-resolved spectra by inverse Compton emission in the pulsar striped wind

Application to Geminga

¹ Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: petri@astro.u-strasbg.fr
² Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany

Received: 22 September 2008
Accepted: 13 May 2009

Abstract

Context. Although discovered 40 years ago, the emission mechanism responsible for the observed pulsar radiation remains unclear. However, high-energy pulsed emission is usually explained in the framework of either the polar cap or the outer gap model. Here we explore an alternative model based on the striped wind.

Aims. The purpose of this work is to study the pulsed component, the light-curves as well as the spectra of the high-energy emission, above 10 MeV, emanating from the striped wind model. Gamma rays are produced by scattering off the soft cosmic microwave background photons on the ultrarelativistic leptons flowing in the current sheets.

Methods. We compute the time-dependent inverse Compton emissivity of the wind, in the Thomson regime, by performing three-dimensional numerical integration in space over the whole striped wind. The phase-dependent spectral variability is then calculated as well as the change in pulse shape when going from the lowest to the highest energies.

Results. Several light curves and spectra of inverse Compton radiation with phase resolved dependence are presented. We apply our model to the well-known gamma-ray pulsar Geminga. We are able to fit the EGRET spectra between 10 MeV and 10 GeV as well as the light curve above 100 MeV with good accuracy.

Conclusions. In the striped wind model, the pulses are a direct consequence of the relativistic beaming effect. It is a simple geometrical model able to explain the very high-energy variability of the phase-resolved spectrum as well as the shape of the associated pulses. Future comparisons with observations at the highest energies and possibly polarization measurements will be important to discriminate between existing models.