Browsing by Author "Fossati, G."
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Item Are relativistic jets monoparametric engines?Georganopoulos, M.; Meyer, E. T.; Fossati, G.; Lister, M. L.We adopt as a working hypothesis that relativistic jets are essentially monoparametric entities, and that their physical properties are a function of a single physical parameter, the same way the physical properties of main sequence stars are mainly a function of the star mass. We propose that the physical parameter is the jet kinetic power, and we use as a proxy for this quantity the low frequency extended radio luminosity (LFERL), an orientation insensitive quantity. We discuss the consequences of this hypothesis for the collective properties of relativistic jets and we show that a blazar sequence should spontaneously emerge on the peak frequency vs luminosity plot as the locus of those sources that are well aligned to the observer’s line of sight. We also show that the sources of the same LFERL should form tracks that start from a location on the blazar sequence and move to lower luminosities and peak frequencies in a way that encodes information about the emitting plasma energetics and kinematics and velocity gradients, as well as about the inverse Compton (IC) emission seed photons. We are currently working on collecting the observations that will allow us to put this idea to the test.Item Clues on Blazars Phenomenology from the FIRST Flat Spectrum Sample(Astronomical Society of the Pacific, 2010) Fossati, G.; Meyer, E. T.We highlight some results of our work on the FIRST Flat Spectrum Sample (FFSS) of blazars, in particular concerning the relationship between their luminosity and Spectral Energy Distribution (SED), including preliminary results on the power of the emission of their Broad Line Region (BLR). The current analysis shows that within the FFSS, which captures at once a broad range of blazar phenomenology, the SED-power correlation which constituted the observational basis of the blazar sequence hypothesis seems to be present. We also find that FFSS BL Lac and FSRQ sources, despite having been selected together, tend to stay separate with respect to several properties, such as SED type and luminosities (e.g. radio, γ-ray, BLR). The BLR analysis suggests that in BL Lac objects the BLR is indeed under-luminous compared with FSRQ. This in turn suggests that ratio between thermal and non-thermal emission in the two classes of objects is different. Finally, we discuss some clues emerging from the study of the sample of blazars detected at GeV γ-rays by Fermi/LAT, focusing again on the question of power of SED properties.Item Using the SED to locate the Gamma-ray emission site of powerful blazars(2012-02-28) Georganopoulos, Markos; Meyer, E. T.; Fossati, G.The location of the Gamma-ray emission of powerful blazars is a matter of active debate. Is the location within the UV emitting sub-pc scale broad line region, or farther out at pc scales where the molecular torus IR emission dominates? We present a diagnostic that connects three observables, the synchrotron and external Compton peak frequencies and the Compton dominance (the ratio of Compton to synchrotron luminosity) to the seed photon energy and energy density. We discuss encouraging preliminary results and discuss how to use our diagnostic to understand the location of the Gamma-ray emission as a function of source power through the use of multiwavelength observations.