Spectral Energy Distribution variation in BL Lacs and FSRQs

Source: arXiv


We present the results of our study of spectral energy distributions (SEDs)
of a sample of ten low- to intermediate-synchrotron-peaked blazars. We
investigate some of the physical parameters most likely responsible for the
observed short-term variations in blazars. To do so, we focus on the study of
changes in the SEDs of blazars corresponding to changes in their respective
optical fluxes. We model the observed spectra of blazars from radio to optical
frequencies using a synchrotron model that entails a log-parabolic distribution
of electron energies. A significant correlation among the two fitted spectral
parameters ($a$, $b$) of log-parabolic curves and a negative trend among the
peak frequency and spectral curvature parameter, $b$, emphasize that the SEDs
of blazars are fitted well by log-parabolic curves. On considering each model
parameter that could be responsible for changes in the observed SEDs of these
blazars, we find that changes in the jet Doppler factors are most important.

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Available from: S. Boeva, Oct 01, 2015
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    ABSTRACT: The BL Lac object 3C 66A was the target of an extensive multiwavelength monitoring campaign from 2003 July through 2004 April (with a core campaign from 2003 September to 2003 December) involving observations throughout the electromagnetic spectrum. Radio, infrared, and optical observations were carried out by the WEBT-ENIGMA collaboration. At higher energies, 3C 66Awas observed in X-rays (RXTE), and at very high energy (VHE) in gamma-rays (STACEE, VERITAS). In addition, the source has been observed with the VLBA at nine epochs throughout the period 2003 September to 2004 December, including three epochs contemporaneous with the core campaign. A gradual brightening of the source over the course of the campaign was observed at all optical frequencies, culminating in a very bright maximum around 2004 February 18. The WEBT campaign revealed microvariability with flux changes of similar to 5% on timescales as short as similar to 2 hr. The source was in a relatively bright state, with several bright flares on timescales of several days. The spectral energy distribution (SED) indicates a v F v peak in the optical regime. A weak trend of optical spectral hysteresis with a trend of spectral softening throughout both the rising and decaying phases has been found. On longer timescales, there appears to be a weak indication of a positive hardness-intensity correlation for low optical fluxes, which does not persist at higher flux levels. The 3-10 keV X-ray flux of 3C 66A during the core campaign was historically high and its spectrum very soft, indicating that the low-frequency component of the broadband SED extends beyond similar to 10 keV. No significant X-ray flux and/or spectral variability was detected. STACEE and Whipple observations provided upper flux limits at > 150 and > 390 GeV, respectively. The 22 and 43 GHz data from the three VLBA epochs made between 2003 September and 2004 January indicate a rather smooth jet with only very moderate internal structure. Evidence for superluminal motion (8.5 +/- 5.6 h(-1) c) was found in only one of six components, while the apparent velocities of all other components are consistent with 0. The radial radio brightness profile suggests a magnetic field decay proportional to r(-1) and, thus, a predominantly perpendicular magnetic field orientation.
    The Astrophysical Journal 09/2005; 631(1). DOI:10.1086/432609 · 5.99 Impact Factor
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    ABSTRACT: We report the BeppoSAX observations of 6 Flat Spectrum Radio Quasars. Three of them have a clear detection up to 100 keV with the PDS instrument. For 4 objects the X-ray spectrum is satisfactorily fitted by a power-law continuum with Galactic absorption. 2251+158 show the presence of absorption higher than the galactic value, while the spectrum of the source 0208-512 shows a complex structure, with evidence of absorption at low energy. We construct the Spectral Energy Distributions adding historical data to the broad band X-ray spectra obtained with $Beppo$SAX and reproduce them with a one-zone Synchrotron-Inverse Compton model (including both SSC and External Compton). The implications are briefly discussed. Comment: 5 figures; ApJ, in press
    The Astrophysical Journal 07/2002; 575(1). DOI:10.1086/341212 · 5.99 Impact Factor
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    ABSTRACT: We demonstrate the importance of near-infrared radiation from hot dust for Compton cooling of electrons/positrons in quasar jets. In our model, we assume that the non-thermal radiation spectra observed in OVV quasars are produced by relativistic electrons/positrons accelerated in thin shells which propagate down the jet with relativistic speeds. We show that the Comptonization of the near-IR flux is likely to dominate the radiative output of OVV quasars in the energy range from tens of keV up to hundreds of MeV, where it exceeds that produced by Comptonization of the UV radiation reprocessed and rescattered in the Broad Emission Line region. The main reason for this lies in the fact that the jet encounters the ambient IR radiation over a relatively large distance as compared to the distance where the energy density of the broad emission line light peaks. In the soft - to mid energy X-ray band, the spectral component resulting from Comptonization of the near-IR radiation joins smoothly with the synchrotron-self-Compton component, which may be responsible for the soft X-ray flux. At the highest observed gamma-ray energies, in the GeV range, Comptonization of broad emission lines dominates over other components. Comment: 23 pages, including 5 Postscript figures and 3 tables, uses aastex. Astrophysical Journal, accepted for publication in the December 20, 2000 issue
    The Astrophysical Journal 08/2000; 545(1). DOI:10.1086/317791 · 5.99 Impact Factor