2019/03/31 by Paul K. H. Yeung, Dieter Horns
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Crab Nebula #Electron #Fermi Gamma-ray Space Telescope #Magnetic field #Nebula #Pulsars and Gravitational Waves Research #RADIUS #Range (aeronautics) #Synchrotron radiation #Telescope #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/ab107a
Original article published in ApJ on 2019 April 23; Erratum (at the back) submitted to ApJ on 2021 February 1
openalex created_date 2019/03/22 · openalex publication_date 2019/04/20 · arxiv created 2021/02/01 · arxiv updated 2021/02/03 · openalex updated_date 2026/08/06
Abstract The Crab Nebula is a bright emitter of non-thermal radiation across the entire accessible range of wavelengths. The spatial and spectral structures of the synchrotron nebula are well-resolved from radio to hard X-ray emission. The unpulsed emission at GeV–TeV energies is mostly produced via inverse-Compton scattering of energetic electrons with the synchrotron-emitted photons. The spatial structure observed at these energies provides insights into the distribution of electrons and indirectly constrains the so-far unknown structure of the magnetic field in the nebula. Analyzing the Large Area Telescope (LAT) data accumulated over ∼9.1 yr with a properly refined model for the Crab pulsar’s spectrum, we determined the 68% containment radius ( R 68 ) of the Crab Nebula to be <?CDATA (0.0330± 0.0025stat-0.0075+0.0012sys)^∘ ?> ( <?CDATA 1\buildrel ′\over. 98± 0\buildrel ′\over. 15stat_-0.^′ 45^+0.^′ 07sys?> ) in the 5–500 GeV band. The estimated systematic uncertainty is based on two factors: (1) different analysis methods, morphological models and event types, and (2) the point-spread function evaluated with observations of Mkn 421. When comparing the Fermi -LAT and High Energy Stereoscopic System results on the spatial extension, we find evidence for an energy-dependent shrinking of the Crab Nebula’s γ -ray extension ( <?CDATA R68∝ EIC-α ?> , where <?CDATA α =0.155± 0.035stat-0.037sys?> ).