On the origin of X-ray spectra in luminous blazars

Journal Article · Tue Dec 10 00:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/779/1/68· OSTI ID:22348488

Sikora, Marek; Janiak, Mateusz; Moderski, Rafał ^[1]; Nalewajko, Krzysztof ^[2]

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1. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw (Poland)
2. JILA, University of Colorado and National Institute of Standards and Technology, UCB 440, Boulder, CO 80309 (United States)

Gamma-ray luminosities of some quasar-associated blazars imply jet powers reaching values comparable to the accretion power even if assuming very strong Doppler boosting and very high efficiency of gamma-ray production. With much lower radiative efficiencies of protons than of electrons, and the recent reports of very strong coupling of electrons with shock-heated protons indicated by particle-in-cell simulations, the leptonic models seem to be strongly favored over the hadronic ones. However, the electron-proton coupling combined with the external-radiation-Compton (ERC) models of gamma-ray production in leptonic models predict extremely hard X-ray spectra, with energy indices α {sub x} ∼ 0. This is inconsistent with the observed 2-10 keV slopes of blazars, which cluster around α {sub x} ∼ 0.6. This problem can be resolved by assuming that electrons can be efficiently cooled down radiatively to non-relativistic energies, or that blazar spectra are entirely dominated by the synchrotron self-Compton (SSC) component up to at least 10 keV. Here, we show that the required cooling can be sufficiently efficient only at distances r < 0.03 pc. SSC spectra, on the other hand, can be produced roughly co-spatially with the observed synchrotron and ERC components, which are most likely located roughly at a parsec scale. We show that the dominant SSC component can also be produced much further than the dominant synchrotron and ERC components, at distances of ≳ 10 pc. Hence, depending on the spatial distribution of the energy dissipation along the jet, one may expect to see γ-ray/optical events with either correlated or uncorrelated X-rays. In all cases the number of e{sup +}e{sup –} pairs per proton is predicted to be very low. The direct verification of the proposed SSC scenario, and particularly the question of the co-spatiality of the SSC component with other spectral components, requires sensitive observations in the hard X-ray band. This is now possible with the deployment of the NuSTAR satellite, providing the required sensitivity to monitor the details of the hard X-ray spectra of blazars in the range where the ERC component is predicted to start dominating over the SSC component.

• OSTI ID: 22348488
• Journal Information: Astrophysical Journal, Vol. 779, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCELERATION
ELECTRON-PROTON INTERACTIONS
ELECTRONS
ENERGY LOSSES
GALAXIES
GAMMA RADIATION
HARD X RADIATION
KEV RANGE
LUMINOSITY
POSITRONS
PROTONS
QUASARS
RELATIVISTIC RANGE
SATELLITES
SIMULATION
SPATIAL DISTRIBUTION
STRONG-COUPLING MODEL
SUPERCONDUCTING SUPER COLLIDER
X-RAY SPECTRA