Volume 640, August 2020
|Number of page(s)||10|
|Published online||10 August 2020|
Inferring the origins of the pulsed γ-ray emission from the Crab pulsar with ten-year Fermi-LAT data⋆
Institute for Experimental Physics, Department of Physics, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
Accepted: 6 June 2020
Context. The Crab pulsar is a bright γ-ray source, which has been detected at photon energies up to ∼1 TeV. Its phase-averaged and phase-resolved γ-ray spectra below 10 GeV exhibit exponential cutoffs, while those above 10 GeV apparently follow simple power laws.
Aims. We re-visit the γ-ray properties of the Crab pulsar with ten-year Fermi Large Area Telescope (LAT) data in the range of 60 MeV–500 GeV. With the phase-resolved spectra, we investigate the origins and mechanisms responsible for the emissions.
Methods. The phaseograms were reconstructed for different energy bands and further analysed using a wavelet decomposition. The phase-resolved energy spectra were combined with the observations of ground-based instruments, such as MAGIC and VERITAS, to achieve a larger energy converage. We fitted power-law models to the overlapping energy spectra from 10 GeV to ∼1 TeV. In the fit, we included a relative cross-calibration of energy scales between air-shower-based gamma-ray telescopes with the orbital pair-production telescope from the Fermi mission.
Results. We confirm the energy-dependence of the γ-ray pulse shape and, equivalently, the phase-dependence of the spectral shape for the Crab pulsar. A relatively sharp cutoff at a relatively high energy of ∼8 GeV is observed for the bridge-phase emission. The E > 10 GeV spectrum observed for the second pulse peak is harder than those for other phases.
Conclusions. In view of the diversity of phase-resolved spectral shapes of the Crab pulsar, we tentatively propose a multi-origin scenario where the polar-cap, outer-gap, and relativistic-wind regions are involved.
Key words: pulsars: individual: Crab pulsar / gamma rays: stars
The data point values in Figs. 1, 3, 4, and 9 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A43
© ESO 2020
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