Fermi Gamma-ray Space Telescope

The Role of the Magnetospheric Structure on the Energy-dependent Light Curves of the Vela Pulsar

Monica Barnard
(Christo Venter, Alice K. Harding and Constantinos Kalapotharakos on behalf of the Fermi LAT Collaboration)


Detection of the Vela pulsar up to ~100 GeV by H.E.S.S. and the Fermi Large Area Telescope (LAT) provides evidence for a curved spectrum. We interpret this spectrum to be the result of curvature radiation by primary particles in the pulsar magnetosphere and current sheet. We present energy-dependent light curves with good resolution for several different parameters using a full emission code, assuming a force-free magnetic field and uniform emissivity. We include a refined calculation of the curvature radius of particle trajectories, which has an influence on the transport, predicted light curves, and spectra. We find that the curvature radii of trajectories associated with the second gamma-ray light curve peak are relatively larger than those associated with the first, leading to larger cutoffs and explaining the disappearance of the first peak at higher energy. We fit model light curves to the radio and energy-dependent gamma-ray data. To address the larger-than-observed prediction of the radio-to-gamma phase lag, we will also present results for a more self-consistent force-free inside and dissipative outside (FIDO) model. Multi-band energy-dependent light curve modeling thus presents an important tool to constrain models of pulsar emission and magnetospheric structure.