2008/12/16 by A. A. Abdo, M. Ackermann, W. B. Atwood +97
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Fermi Gamma-ray Space Telescope #Gamma-ray bursts and supernovae #Magnetosphere #Nebula #Nuclear physics #Physics #Plasma #Pulsar #Pulsars and Gravitational Waves Research #Sky #Stars #Telescope #Vela #astro-ph
paper · pdf · doi:10.1088/0004-637x/696/2/1084
12 pp, accepted for appearance in the Astrophysical Journal; R.W.Romani & M. Razzano, contact authors
arxiv created 2008/12/16 · openalex publication_date 2009/04/22 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/08
The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new γ-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E ⩾ 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of Γ = 1.51 +0.05 −0.04 with an exponential cutoff at E c = 2.9 ± 0.1 GeV. Spectral fits with generalized cutoffs of the form require b ⩽ 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.