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تسجيل مستخدم جديدRadio and gamma-ray emission in faint BL Lacs
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The advent of Fermi is changing our understanding on the radio and gamma-ray emission in Active Galactic Nuclei. In fact, contrary to previous campaigns, Fermi mission reveals that BL Lac objects are the most abundant emitters in gamma-ray band. However, since they are relatively weak sources, most of their parsec scale structure as their multifrequency properties are poorly understood and/or not systematically investigated. Our main goal is to analyse, using a multiwavelength approach, the nuclear properties of an homogeneous sample of 42 faint BL Lacs, selected, for the first time in literature, with no constraint on their radio and gamma-ray flux densities/emission. We began asking and obtaining new VLBA observations at 8 and 15 GHz for the whole sample. We derived fundamental parameters as radio flux densities, spectral index information, and parsec scale structure. Moreover, we investigated their gamma-ray emission properties using the 2LAT Fermi results. Here, we report our preliminary results on the radio and gamma-ray properties of this sample of faint BL Lacs. In the next future, we will complete the multiwavelength analysis.
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Blazars represent the most abundant class of high-energy extragalactic $gamma$-ray sources. The subset of blazars known as BL Lac objects is on average closer to Earth and characterized by harder spectra at high energy than the whole sample. The frac
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We present the spectral signatures of the Bethe-Heitler pair production ($pe$) process on the spectral energy distribution (SED) of blazars, in scenarios where the hard $gamma$-ray emission is of photohadronic origin. If relativistic protons interact
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The spectral energy distribution of blazars around the synchrotron peak can be well described by the log-parabolic model that has three parameters: peak energy ($E_textrm{p}$), peak luminosity ($L_textrm{p}$) and the curvature parameter ($b$). It has
been suggested that $E_textrm{p}$ shows relations with $L_textrm{p}$ and $b$ in several sources, which can be used to constrain the physical properties of the emitting region and/or acceleration processes of the emitting particles. We systematically study the $E_textrm{p}$-$L_textrm{p}$ and $E_textrm{p}$-(1$/b$) relations for 14 BL Lac objects using the 3-25~keV $RXTE$/PCA and 0.3-10~keV $Swift$/XRT data. Most objects (9/14) exhibit positive $E_textrm{p}$-$L_textrm{p}$ correlations, three sources show no correlation, and two sources display negative correlations. In addition, most targets (7/14) present no correlation between $E_textrm{p}$ and 1$/b$, five sources pose negative correlations, and two sources demonstrate positive correlations. 1ES~1959+650 displays two different $E_textrm{p}$-$L_textrm{p}$ relations in 2002 and 2016. We also analyze $E_textrm{p}$-$L_textrm{p}$ and $E_textrm{p}$-(1$/b$) relations during flares lasting for several days. The $E_textrm{p}$-$L_textrm{p}$ relation does not exhibit significant differences between flares, while the $E_textrm{p}$-(1$/b$) relation varies from flare to flare. For the total sample, when $L_textrm{p}$ < $textrm{10}^textrm{45} textrm{erg} textrm{s}^textrm{-1}$, there seems to be a positive $E_textrm{p}$-$L_textrm{p}$ correlation. $L_textrm{p}$ and the slope of $E_textrm{p}$-$L_textrm{p}$ relation present an anti-correlation, which indicates that the causes of spectral variations might be different between luminous and faint sources. $E_textrm{p}$ shows a positive correlation with the black hole mass. We discuss the implications of these results.
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