Nature of $gamma$-ray variability in blazars. (arXiv:1911.08198v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bhatta_G/0/1/0/all/0/1">Gopal Bhatta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dhital_N/0/1/0/all/0/1">Niraj Dhital</a>
We present an in-depth and systematic analysis of a sample of 20 powerful
blazars, including 12 BL Lacs and 8 flat spectrum radio quasars, utilizing
Fermi/LAT observations from the period 2008–2018 using various analysis tools
such as flux distribution, symmetry analysis, and time series analysis. Results
show that blazars with steeper $gamma$-ray spectral indexes are found to be
more variable; and the $gamma$-ray flux distribution closely resemble both
normal and lognormal probability distribution functions. The statistical
variability properties of the sources as studied by power spectral density
analysis are consistent with flicker noise ($P(nu)propto1/nu$) — an
indication of long-memory processes at work. Statistical analysis of the
distribution of flux rise and decay rates in the light curves of the sources,
aimed at distinguishing between particle acceleration and energy dissipation
timescales, counter-intuitively suggests that both kinds of rates follow a
similar distribution and the derived mean variability timescales are in the
order of a few weeks. The corresponding emission region size is used to
constrain location of $gamma$-ray production sites in the sources to be a few
parsecs. Additionally, using Lomb-Scargle periodogram aided with extensive
Monte Carlo simulations, we detected year timescale quasi-periodic oscillations
in the sources S5 0716+714, Mrk 421, ON +325, PKS 1424-418 and PKS 2155-304;
and the detection significance was computed taking proper account of the
red-noise and other artifacts inherent in the observations. We explain our
results in the light of current blazar models with relativistic shocks
propagating down the jet viewed close to the line of sight.
We present an in-depth and systematic analysis of a sample of 20 powerful
blazars, including 12 BL Lacs and 8 flat spectrum radio quasars, utilizing
Fermi/LAT observations from the period 2008–2018 using various analysis tools
such as flux distribution, symmetry analysis, and time series analysis. Results
show that blazars with steeper $gamma$-ray spectral indexes are found to be
more variable; and the $gamma$-ray flux distribution closely resemble both
normal and lognormal probability distribution functions. The statistical
variability properties of the sources as studied by power spectral density
analysis are consistent with flicker noise ($P(nu)propto1/nu$) — an
indication of long-memory processes at work. Statistical analysis of the
distribution of flux rise and decay rates in the light curves of the sources,
aimed at distinguishing between particle acceleration and energy dissipation
timescales, counter-intuitively suggests that both kinds of rates follow a
similar distribution and the derived mean variability timescales are in the
order of a few weeks. The corresponding emission region size is used to
constrain location of $gamma$-ray production sites in the sources to be a few
parsecs. Additionally, using Lomb-Scargle periodogram aided with extensive
Monte Carlo simulations, we detected year timescale quasi-periodic oscillations
in the sources S5 0716+714, Mrk 421, ON +325, PKS 1424-418 and PKS 2155-304;
and the detection significance was computed taking proper account of the
red-noise and other artifacts inherent in the observations. We explain our
results in the light of current blazar models with relativistic shocks
propagating down the jet viewed close to the line of sight.
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