Blazars are a small fraction of all extragalactic sources but, unlike other objects, they are strong emitters across the entire electromagnetic spectrum. Recent data in the microwave region of the electromagnetic spectrum have become available to allow for systematic studies of blazars over large cosmological volumes. This frequency band is indeed particularly suited for the selection of blazars since at these frequencies the contamination from radio extended components with steep spectra is no longer present and the emission from the accretion process is negligible. During the first 3 months of scientific operations Fermi-LAT detected 106 bright, high-galactic latitude (| b |> 10 deg) AGNs with high significance. In this study we investigate the possible relations between the microwave and the gamma-ray emissions for Fermi-LAT detected AGNs belonging to WMAP 5th year bright source catalog.
Blazars are rare extragalactic objects as they are a subset of radio loud QSOs, which in turn are only ≈10% of radio-quiet QSOs and Seyfert galaxies that are found in large numbers at optical and at X-ray frequencies. Despite that, the strong emission at all wavelengths that characterizes blazars, makes them the dominant type of extragalactic sources in those energy windows where the accretion onto a supermassive black hole, or other thermal mechanisms, do not produce significant radiation. For instance, in the microwave band, [1] showed that blazars are the largest population of extragalactic objects (see also Toffolatti et al. [2]). The same is true in the γ-ray band [3] and at TeV energies where BL Lac objects are the most frequent type of sources found in the high Galactic latitude sky.
Blazars have been known and studied in different energy windows for over 40 years, however, many questions still remain open about their physics and demographics, e.g., how are jets made and how are they accelerated? How are the relativistic particles accelerated and why is the maximum acceleration so much higher in BL Lacs? What are the mechanisms producing blazar variability and what is the blazar duty-cycle?
We investigate these problematics using a multiwavelength approach through WMAP (µ-wave) and Fermi (γ-ray) observations. Primordial photons are redshifted to µ-wave frequencies due to the Universe expansion and we see these photons as cosmic background in µ-wave band. Tiny inhomogeneities in the early universe left their imprint on the CMB in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters (e.g. total energy density and curvature of the universe). The ability of the present and upcoming CMB experiments to determine the cosmological parameters requires a careful cleaning of the CMB maps from the galactic and extra-galactic foregrounds . This cleaning pro-duces very useful bright source catalogs useful to our scopes.
The microwave frequency range is, moreover, likely the best region of the electromagnetic spectrum to pursue statistical studies of blazars since it is least affected by the superposition of spectral components of different nature like e.g. steep radio emission from the extended part of the jet, non-nuclear optical emission from the host galaxy or optical/UV and soft X-ray emission from an accretion disk.
We have already studied a µ-wave selected sample and its X-ray properties [4] and verified that the µwave flux is tightly correlated with the X-ray one. Given the currently accepted emission mechanisms, such as Synchrotron Self Compton, as responsible for the broad-band blazar emission, we would like to investigate a possible relation among µ-wave and γ-ray fluxes.
Our strategy consists in building a complete sample of blazars selected in the µ-wave band, starting from the WMAP bright source catalogues periodically released by the WMAP Team. Than we study the properties of this µ-wave selected sample of jet-dominated AGN looking for synchrotron peak distribution of the sources, γ-ray spectral index estimates, possible relations between µ-wave fluxes and X-ray, γ-ray duty cycle, α µγ . As in Pittori et al. [5], we take into account the constraints from the observed extragalactic gamma-ray background on the maximum duty cycle allowed for the selected sample of WMAP Blazars.
Wilkinson Microwave Anisotropic Prope (WMAP) [6] satellite provides an all-sky survey of the millimeter-wave sky and its point source catalogs are valuable for the study of flat-spectrum radio sources. In this work we use the five-year catalogue of 390 foreground sources (WMAP5) [7]. We define the complete sample as including all sources in the WMAP5 catalogue with flux at 41 GHz larger than 0.9 Jy. We define a flux limited sample using the source fluxes as observed in the WMAP 41 GHz channel to have a compromise between sensitivity, completeness and the need to use a high frequency band, to avoid the steep radio components. Highest frequency channels in WMAP survey (61, 94 GHz) have less objects and are less deep in flux with respect to lower frequencies (23, 33, 41 GHz).
F ermi Gamma-ray Space Telescope is an international mission suited for the study of γ-ray emission in the Universe. The LAT, the primary instrument, is an imaging, wide field-of-view telescope, covering the energy range from below 20 MeV to more than 300 GeV with a sensitivity that exceeds EGRET by a factor of 30 or more. F ermi satellite commonly observes the sky in scanning mode: on a given orbit, the LAT will sweep the sky 35 degree away from the orbital plane, covering 75% of the sky. At the end of the orbit, F ermi will rock to 35 degree on the other side of the orbital. Therefore the entire sky is covered every three hours providing an uniform sky coverage within few orbit [8]. Thanks to the improved instrument performance (point spread function, effective area, large field o
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