Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars

By P. Giommi, G. Polenta, A. Lähteenmäki, D. Thompson, M. Capalbi, S. Cutini, D. Gasparrini, J. González-Nuevo, J. León-Tavares, M. López-Caniego and 85 more. 2011

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We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the -ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, withh i 0 up to about 70 GHz, above which it steepens toh i 0:65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency ( S ) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples withh S i = 10 13:1 0:1 Hz, while the mean inverse-Compton peak frequency,h IC i, ranges from 10 21 to 10 22 Hz. The distributions of S and of IC of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with -ray selected blazars peaking at 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection e ect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the -ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and S predicted by the blazar sequence.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/ce01931d56bceff283fc7403d0b0c4902ebbdbdc

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Citations in the corpus

A simplified view of blazars: clearing the fog around long‐standing selection effects (2011, methodology): “…values as high as νSpeak > ∼ 10 18 Hz and its shape varies strongly depending on the selection band (that is radio, X-ray or γ-ray: Abdo et al. 2010c; Giommi et al. 2011). c© 2011 RAS, MNRAS 000, 1–14 Some of these differences have been explained by socalled unified schemes, which posit that BL…”
Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program (2017, background): “…extreme characteristics across the electromagnetic spectrum, such as ultra-luminous (up to ∼ 1050erg s−1) emission (e.g., Abdo et al. 2010c, 2011; Giommi et al. 2012; Sentürk et al. 2013), high amplitudes of variability on various timescales as short as several minutes (e.g., HESS…”
Fermi Large Area Telescope Fourth Source Catalog (2019, methodology): “…Schinzel et al. 2015, 2017) and below (see, e.g., Massaro et al. 2013; Nori et al. 2014; Giroletti et al. 2016), or using submillimeter (see, e.g., Giommi et al. 2012; López-Caniego et al. 2013) and infrared observations (see, e.g., Massaro et al. 2011, 2012a, 2012b; D’Abrusco et al. 2014;…”