Systematic Physical Characterization of the Gamma-Ray Spectra of 2FHL Blazars. (arXiv:1901.03494v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Berg_J/0/1/0/all/0/1">Jacobus P. van den Berg</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Boettcher_M/0/1/0/all/0/1">Markus Boettcher</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Dominguez_A/0/1/0/all/0/1">Alberto Dominguez</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Moya_M/0/1/0/all/0/1">Marcos Lopez-Moya</a> (2) ((1) North-West University, South Africa, (2) Universidad Complutense de Madrid, Spain)
We test different physically motivated models for the spectral shape of the
$gamma$-ray emission in a sample of 128 blazars with known redshifts detected
by the Fermi Large Area Telescope (LAT) at energies above 50 GeV. The first
nine years of LAT data in the energy range from 300 MeV to 2 TeV are analyzed
in order to extend the spectral energy coverage of the 2FHL blazars in our
sample. We compare these spectral data to four leptonic models for the
production of $gamma$-rays through Compton scattering by a population of
electrons with different spectral shapes. In the first three models we consider
Compton scattering in the Thomson regime with different acceleration mechanisms
for the electrons. In the fourth model we consider Compton scattering by a pure
power law distribution of electrons with spectral curvature due to scattering
in the Klein-Nishina regime. The majority of blazar $gamma$-ray spectra are
preferentially fit with either a power law with exponential cut-off in the
Thomson regime or a power law electron distribution with Compton scattering in
the Klein-Nishina regime, while a log-parabola with a low-energy power-law and
broken power-law spectral shape in the Thomson regime appears systematically
disfavoured, which is likely a consequence of the restriction to pure Thomson
scattering which we imposed on those models. This finding may be an indication
that the $gamma$-ray emission from FSRQs in the 2FHL catalog is dominated by
Compton scattering of radiation from the dusty torus, while in the case of BL
Lac objects, it is dominated by synchrotron self-Compton radiation.
We test different physically motivated models for the spectral shape of the
$gamma$-ray emission in a sample of 128 blazars with known redshifts detected
by the Fermi Large Area Telescope (LAT) at energies above 50 GeV. The first
nine years of LAT data in the energy range from 300 MeV to 2 TeV are analyzed
in order to extend the spectral energy coverage of the 2FHL blazars in our
sample. We compare these spectral data to four leptonic models for the
production of $gamma$-rays through Compton scattering by a population of
electrons with different spectral shapes. In the first three models we consider
Compton scattering in the Thomson regime with different acceleration mechanisms
for the electrons. In the fourth model we consider Compton scattering by a pure
power law distribution of electrons with spectral curvature due to scattering
in the Klein-Nishina regime. The majority of blazar $gamma$-ray spectra are
preferentially fit with either a power law with exponential cut-off in the
Thomson regime or a power law electron distribution with Compton scattering in
the Klein-Nishina regime, while a log-parabola with a low-energy power-law and
broken power-law spectral shape in the Thomson regime appears systematically
disfavoured, which is likely a consequence of the restriction to pure Thomson
scattering which we imposed on those models. This finding may be an indication
that the $gamma$-ray emission from FSRQs in the 2FHL catalog is dominated by
Compton scattering of radiation from the dusty torus, while in the case of BL
Lac objects, it is dominated by synchrotron self-Compton radiation.
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