Unifying models for X-ray selected and Radio selected BL Lac Objects

Abstract

We discuss alternative interpretations of the differences in the Spectral Energy Distributions (SEDs) of BL Lacs found in complete Radio or X-ray surveys. A large body of observations in different bands suggests that the SEDs of BL Lac objects appearing in X-ray surveys differ from those appearing in radio surveys mainly in having a (synchrotron) spectral cut-off (or break) at much higher frequency. In order to explain the different properties of radio and X-ray selected BL Lacs Giommi and Padovani proposed a model based on a common radio luminosity function. At each radio luminosity, objects with high frequency spectral cut-offs are assumed to be a minority. Nevertheless they dominate the X-ray selected population due to the larger X-ray-to-radio-flux ratio. An alternative model explored here (reminiscent of the orientation models previously proposed) is that the X-ray luminosity function is "primary" and that at each X-ray luminosity a minority of objects has larger radio-to-X-ray flux ratio. The predictions of the two scenarios, computed via a Montecarlo technique, are compared with the observed properties of BL Lacs in the two samples extracted respectively from the 1 Jy radio survey and the Einstein Slew Survey. We show that both models can explain a number but not all the observed features. We then propose a completely new approach, based on the idea that the physical parameter which governs the shape of the SEDs, is (or is associated with) the bolometric luminosity. Assuming an empirical relation between spectral shape and luminosity we show that the observational properties of the two surveys can be reproduced at least with the same accuracy as the two previous models.

21 pages, when TeX-ed including tables (3) and figures (8). MNRAS latex. mn.sty and psfig.sty included. Accepted for pubblication in MNRAS. Also available at http://www.sissa.it/~fossati/pub_list.html

Cited by in corpus (53)

• The blazar sequence: a new perspective
• The HST Survey of BL Lacertae Objects. II. Host Galaxies
• Hard X-ray properties of blazars
• Extreme synchrotron BL Lac objects
• The Deep X-ray Radio Blazar Survey (DXRBS). I. Methods and First Results
• TeV candidate BL Lac objects
• From the Blazar Sequence to the Blazar Envelope: Revisiting the Relativistic Jet Dichotomy in Radio-loud AGN
• ASCA Observations of Blazars and Multiband Analysis
• The RGB Sample of Intermediate BL Lacs
• The nature of the Diffuse Gamma-Ray Background
• Six years of BeppoSAX observations of blazars: a spectral catalog
• Black Hole Masses and Host Galaxy Evolution of Radio-loud Active Galactic Nuclei
• The Blazar Sequence and the Cosmic Gamma-Ray Background Radiation in the Fermi Era
• Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources
• The Deep X-Ray Radio Blazar Survey (DXRBS). III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars
• Analysis of 6cm VLBI polarization observations of a complete sample of northern BL Lacertae Objects
• The NuSTAR Extragalactic Survey: A First Sensitive Look at the High-Energy Cosmic X-ray Background Population
• The Sedentary Multi-Frequency Survey. I. Statistical Identification and Cosmological Properties of HBL BL Lacs
• The Blazar Sequence: Validity and Predictions
• PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
• A Viewing Angle - Kinetic Luminosity Unification Scheme For BL Lacertae Objects
• Multi-band optical variability studies of BL Lacertae
• Unidentified sources in the Fermi-LAT second source catalog: the case for DM subhalos
• Non-thermal Cosmic Backgrounds from Blazars: the contribution to the CMB, X-ray and gamma-ray Backgrounds
• The REX survey: a search for Radio Emitting X-ray sources
• Multi-band optical variability of three TeV Blazars on Diverse Timescales
• Constraints on the Very High Energy Emission from BL Lacertae Objects
• The Contribution of Blazars to the Extragalactic Diffuse Gamma-ray Background and Their Future Spatial Resolution
• Dark matter subhaloes as gamma-ray sources and candidates in the first Fermi-LAT catalogue
• The recognition of blazars and the blazar spectral sequence
• Balancing the Cosmic Energy Budget: The Cosmic X-ray Background, Blazars and the Compton Thick AGN Fraction
• Current and Future Constraints on Dark Matter from Prompt and Inverse-Compton Photon Emission in the Isotropic Diffuse Gamma-ray Background
• Radiative signature of magnetic fields in internal shocks
• HST Observations of the Host Galaxies of BL Lacertae Objects
• A Search for TeV Gamma-Ray Emission from High-Peaked Flat Spectrum Radio Quasars Using the Whipple Air-Cherenkov Telescope
• Multiwavelength Properties of Blazars
• Unifying B2 radio galaxies with BL Lac objects
• Long-term optical polarization variability of the tev blazar 1es~1959+650
• Discovery of the most X-ray luminous quasar SRGE J170245.3+130104 at redshift z$\approx 5.5$
• Correlation between Fermi/LAT gamma-ray and 37 GHz radio properties of northern AGN averaged over 11 months
• Prospects for Very High Energy Blazar Survey by the Next Generation Cherenkov Telescopes
• Distributions of Gamma-Ray Bursts and Blazars in the $L_{\mathrm{p}}-E_{\mathrm{p}}$ Plane and Possible Implications for their Radiation Physics
• Testing the Blazar Paradigm: ASCA Observations of FSRQs with Steep Soft X-ray Spectra
• Chandra Observations of the X-ray Environment of BL Lacs
• Variations in the broadband spectra of BL Lac objects: millimetre observations of an X-ray-selected sample
• The synchrotron peak shift during high-energy flares of blazars
• Searching for the most distant blazars with the Fermi Gamma-ray Space Telescope
• Characterizing the optical nature of the blazar S5 1803+784 during its 2020 flare
• Rotation of the optical polarization angle associated with the 2008 γ-ray flare of blazar w comae
• Multiwavelength flaring activity of PKS1510-089
• Observational Signatures of Gamma Rays from Bright Blazars and Wakefield Theory
• Progress in understanding Blazars from BeppoSAX observations
• The FRII Broad Line Seyfert 1 Galaxy: PKSJ 1037-2705