Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...710...24s&link_type=abstract
The Astrophysical Journal, Volume 710, Issue 1, pp. 24-28 (2010).
Astronomy and Astrophysics
Astronomy
8
Bl Lacertae Objects: General, Galaxies: Jets, Quasars: General, X-Rays: Galaxies
Scientific paper
Using public Fermi Large Area Telescope (LAT) and Swift Burst Alert Telescope observations, we constructed the first sample of blazars selected at both hard X-rays and gamma rays. Studying its spectral properties, we find a luminosity dependence of the spectral slopes at both energies. Specifically, luminous blazars, generally classified as flat spectrum radio quasars, have hard continua in the medium-hard X-ray range but soft continua in the LAT gamma-ray range (photon indices Γ X <~ 2 and Γ G >~ 2), while lower luminosity blazars, classified as BL Lacs, have opposite behavior, i.e., soft X-ray and hard gamma-ray continua (Γ X >~ 2.4 and Γ G < 2). The trends are confirmed by detailed Monte Carlo simulations explicitly taking into account the observational biases of both instruments. Our results support the so-called blazar sequence which was originally based on radio samples of blazars and radio luminosities. We also argue that the X-ray-to-gamma-ray continua of blazars may provide independent insights into the physical conditions around the jet, complementing/superseding the ambiguities of the traditional classification based on optical properties.
Ajello Marco
Barthelmy Scott
Baumgartner Wayne
Donato Davide
Gehrels Neil
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