Abstract
We develop a simple two-zone interpretation of the broadband baseline Crab nebula spectrum between 10−5 eV and ~ 100 TeV by using two distinct log-parabola energetic electrons distributions. We determine analytically the very-high energy photon spectrum as originated by inverse-Compton scattering of the far-infrared soft ambient photons within the nebula off a first population of electrons energized at the nebula termination shock. The broad and flat 200 GeV peak jointly observed by Fermi/LAT and MAGIC is naturally reproduced. The synchrotron radiation from a second energetic electron population explains the spectrum from the radio range up to ~ 10 keV. We infer from observations the energy dependence of the microscopic probability of remaining in proximity of the shock of the accelerating electrons.
Highlights
The steady-state gamma-ray emission of the Crab Nebula has been observed in the past decade by a number of ground-based observatories, i.e., HEGRA [1], MAGIC [2], HESS II [3] and VERITAS [4]
We propose a two-zone model with two distinct populations of energetic electrons having two distinct log-parabola distributions injected at the same energy to explain the broadband spectrum from 10−5 eV up to 100 TeV; the MeV region exceeds our prediction
The broad and flat VHE peak at 200 GeV joining the TeV-band spectrum observed with MAGIC (0.05 − 30 TeV) with the GeV-band spectrum obtained with Fermi/LAT (1 − 200 GeV) has been empirically modelled with a modified log-parabola with an additional freeparameter that is not physically justified [2]
Summary
The steady-state gamma-ray emission of the Crab Nebula has been observed in the past decade by a number of ground-based observatories, i.e., HEGRA [1], MAGIC [2], HESS II [3] and VERITAS [4]. The broad and flat VHE peak at 200 GeV joining the TeV-band spectrum observed with MAGIC (0.05 − 30 TeV) with the GeV-band spectrum obtained with Fermi/LAT (1 − 200 GeV) has been empirically modelled with a modified log-parabola with an additional freeparameter that is not physically justified [2]. We show that such VHE peak is naturally explained by inverse-Compton scattering off monochromatic Infra-Red ambient photons within the nebula of a log-parabola distribution of electrons.
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