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تسجيل مستخدم جديدInfluence of Energy-Dependent Particle Diffusion on the X-ray spectral curvature of MKN 421
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The X-ray spectral curvature of blazars is traditionally explained by an empirical log-parabola function characterized by three parameters, namely the flux, curvature and spectral index at a given energy. Since their exact relationship with the underlying physical quantities is unclear, interpreting the physical scenario of the source through these parameters is difficult. To attain an insight on the X-ray spectral shape, we perform a detailed study of the X-ray spectra of the blazar MKN 421, using an analytical model where the electron diffusion from the particle acceleration site is energy-dependent. The resultant synchrotron spectrum is again determined by three parameters, namely, the energy index of the escape time scale, the quantity connecting the electron energy to the observed photon energy and the normalization. The X-ray observations of MKN 421, during July 2012 - April 2013 by NuSTAR and Swift-XRT are investigated using this model and we find a significant correlation between model parameters and the observational quantities. Additionally, a strong anti-correlation is found between the fit parameters defining the spectral shape, which was not evident from earlier studies using empirical models. This indicates the flux variations in MKN 421 and possibly other blazars, may arise from a definite physical process that needs to be further investigated.
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The X-ray observations of Mkn 421 show significant spectral curvature that can be reproduced by a log-parabola function. The spectra can also be fitted by an analytical model considering synchrotron emission from an electron distribution that is acce
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nderstand the underlying particle energy distribution. Methods: We study the correlations between the UV and gamma bands with the X-ray band using the z-transformed discrete correlation function. We model the underlying particle spectrum with a single population of electrons emitting synchrotron radiation, and do a statistical fitting of the simultaneous, time-resolved data from the Swift-XRT and the NuSTAR. Results: There was rapid flux variability in the X-ray band, with a minimum doubling timescale of $1.69 pm 0.13$ hrs. There were no corresponding flares in UV and gamma bands. The variability in UV and gamma rays are relatively modest with $ sim 8 % $ and $sim 16 % $ respectively, and no significant correlation was found with the X-ray light curve. The observed X-ray spectrum shows clear curvature which can be fit by a log parabolic spectral form. This is best explained to originate from a log parabolic electron spectrum. However, a broken power law or a power law with an exponentially falling electron distribution cannot be ruled out either. Moreover, the excellent broadband spectrum from $0.3-79$ keV allows us to make predictions of the UV flux. We find that this prediction is compatible with the observed flux during the low state in X-rays. However, during the X-ray flares, the predicted flux is a factor of $2-50$ smaller than the observed one. This suggests that the X-ray flares are plausibly caused by a separate population which does not contribute significantly to the radiation at lower energies. Alternatively, the underlying particle spectrum can be much more complex than the ones explored in this work.
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