FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE CRAB PULSAR AND NEBULA

By A. Abdo, M. Ackermann, M. Ajello, W. Atwood, M. Axelsson, L. Baldini, J. Ballet, G. Barbiellini, M. Baring, D. Bastieri and 182 more. 2009

232 citations recorded by the source corpus.

We report on γ-ray observations of the Crab Pulsar and Nebula using 8 months of survey data with the Fermi Large Area Telescope (LAT). The high quality light curve obtained using the ephemeris provided by the Nançay and Jodrell Bank radio telescopes shows two main peaks stable in phase with energy. The first γ-ray peak leads the radio main pulse by (281 ± 12 ± 21) μs, giving new constraints on the production site of non-thermal emission in pulsar magnetospheres. The first uncertainty is due to γ-ray statistics, and the second arises from the rotation parameters. The improved sensitivity and the unprecedented statistics afforded by the LAT enable precise measurement of the Crab Pulsar spectral parameters: cut-off energy at Ec = (5.8 ± 0.5 ± 1.2) GeV, spectral index of Γ = (1.97 ± 0.02 ± 0.06) and integral photon flux above 100 MeV of (2.09 ± 0.03 ± 0.18) × 10−6 cm−2 s−1. The first errors represent the statistical error on the fit parameters, while the second ones are the systematic uncertainties. Pulsed γ-ray photons are observed up to ∼ 20 GeV which precludes emission near the stellar surface, below altitudes of around 4–5 stellar radii in phase intervals encompassing the two main peaks. A detailed phase-resolved spectral analysis is also performed: the hardest emission from the Crab Pulsar comes from the bridge region between the two γ-ray peaks while the softest comes from the falling edge of the second peak. The spectrum of the nebula in the energy range 100 MeV–300 GeV is well described by the sum of two power laws of indices Γsync = (3.99 ± 0.12 ± 0.08) and ΓIC = (1.64 ± 0.05 ± 0.07), corresponding to the falling edge of the synchrotron and the rising edge of the inverse Compton (IC) components, respectively. This latter, which links up naturally with the spectral data points of Cherenkov experiments, is well reproduced via IC scattering from standard magnetohydrodynamic nebula models, and does not require any additional radiation mechanism.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7b08fe3c0f7aa22c69b3617a4ad2857497fbc6cf

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Citations in the corpus

THE FIRST FERMI LAT SUPERNOVA REMNANT CATALOG (2015, background): “…so we compared our results to the fluxes, indices, localizations, and extensions for extended sources that were reported in these publications (Abdo et al. 2010d; Lande et al. 2012; Castro & Slane 2010; Abdo et al. 2010c,e,f; Giordano et al. 2012; Katsuta et al. 2012; Brandt & Fermi-LAT…”
THE FIRST FERMI-LAT CATALOG OF SOURCES ABOVE 10 GeV (2013, methodology): “The fifth radio galaxy, Cen A, is exceptional because of its proximity and also a presence of γ -ray emitting giant lobes clearly resolved with the LAT (Abdo et al. 2010d).”
FERMI LARGE AREA TELESCOPE FIRST SOURCE CATALOG (2010, methodology): “The association between GeV γ-ray PSRs and the PWNs visible in TeV γ-rays seems well established, as has already been discussed in Abdo et al. (2010m).”
THE SECOND FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS (2013, background): “The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope did not just confirm the expectation: by discovering dozens of radio-quiet gamma-ray pulsars and millisecond pulsars (MSPs, thought to be old pulsars spun up to rapid periods via accretion from a companion, Alpar et al. 1982), the”
THE FIRST FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS (2009, methodology): “The LAT is sensitive to gamma rays with energies in the range from 20 MeV to greater than 300 GeV, and its on-axis effective area is ∼ 8000 cm2 for E > 1 GeV.”
GAMMA-RAY ACTIVITY IN THE CRAB NEBULA: THE EXCEPTIONAL FLARE OF 2011 APRIL (2011, methodology): “The spectrum of the inverse-Compton component softens significantly with respect to a power law at higher energies, as expected from measurements at very high energy (VHE) gamma rays (Aharonian et al. 2006; Zanin et al. 2011; Abdo et al. 2010a).”
THE FERMI LARGE AREA TELESCOPE ON ORBIT: EVENT CLASSIFICATION, INSTRUMENT RESPONSE FUNCTIONS, AND CALIBRATION (2012, methodology): “For comparison the intensity of the extragalactic diffuse γ-ray emission measured by the LAT (Abdo et al. 2010f) is overlaid to demonstrate the many orders of background suppression necessary to distinguish it from particle background.”