Inferring the origins of the pulsed γ-ray emission from the Crab pulsar with ten-year Fermi-LAT data
Abstract
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.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- August 2020
- DOI:
- 10.1051/0004-6361/202038166
- arXiv:
- arXiv:2004.07669
- Bibcode:
- 2020A&A...640A..43Y
- Keywords:
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- pulsars: individual: Crab pulsar;
- gamma rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Original article published in A&