251 research outputs found
Multi-wavelength Intra-day Variability and Quasi-periodic Oscillation in Blazars
We reviewed multi-wavelength blazars variability and detection of
quasi-periodic oscillations on intra-day timescales. The variability timescale
from few minutes to up to less than a days is commonly known as intra-day
variability. These fast variations are extremely useful to constrain the size
of emitting region, black hole mass estimation, etc. It is noticed that in
general blazars show intra-day variability in the complete electromagnetic
spectrum. But some class of blazars either do not show or show very little
intra-day variability in a specific band of electromagnetic spectrum. Blazars
show rarely quasi-periodic oscillations in time series data in optical and
X-ray bands. Other properties and emission mechanism of blazars are also
briefly discussed.Comment: Invited Review; Submitted to Galaxies; a special issue on
Microvariability of Blazar
X-ray Flux and Spectral Variability of the TeV Blazars Mrk 421 and PKS 2155-304
We reviewed X-ray flux and spectral variability properties studied to date by
various X-ray satellites for Mrk 421 and PKS 2155-304, which are TeV emitting
blazars. Mrk 421 and PKS 2155-304 are the most X-ray luminous blazars in the
northern and southern hemispheres, respectively. Blazars show flux and spectral
variabilities in the complete electromagnetic spectrum on diverse timescales
ranging from a few minutes to hours, days, weeks, months and even several
years. The flux and spectral variability on different timescales can be used to
constrain the size of the emitting region, estimate the super massive black
hole mass, find the dominant emission mechanism in the close vicinity of the
super massive black hole, search for quasi-periodic oscillations in time series
data and~several other physical parameters of blazars. Flux and spectral
variability is also a dominant tool to explain jet as well as disk emission
from blazars at different epochs of observations.Comment: 15 pages, Published in the special issue "X-Ray Flux and Spectral
Variability of Blazars" of Galaxies Journa
X-ray Intraday Variability of Five TeV Blazars with NuSTAR
We have examined 40 NuSTAR light curves (LCs) of five TeV emitting high
synchrotron peaked blazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650 and
PKS 2155-304. Four of the blazars showed intraday variability in the NuSTAR
energy range of 3-79 keV. Using an auto correlation function analysis we
searched for intraday variability timescales in these LCs and found indications
of several between 2.5 and 32.8 ks in eight LCs of Mrk 421, a timescale around
8.0 ks for one LC of Mrk 501, and timescales of 29.6 ks and 57.4 ks in two LCs
of PKS 2155-304. The other two blazars' LCs do not show any evidence for
intraday variability timescales shorter than the lengths of those observations,
however, the data was both sparser and noisier, for them. We found positive
correlations with zero lag between soft (3-10 keV) and hard (10-79 keV) bands
for most of the LCs, indicating that their emissions originate from the same
electron population. We examined spectral variability using a hardness ratio
analysis and noticed a general "harder-when-brighter" behavior. The 22 LCs of
Mrk 421 observed between July 2012 and April 2013 show that this source was in
a quiescent state for an extended period of time and then underwent an
unprecedented double peaked outburst while monitored on a daily basis during 10
- 16 April 2013. We briefly discuss models capable of explaining these blazar
emissions.Comment: 21 pages, 4 figures, 4 tables, Accepted for Publication in Ap
Multi-wavelength Temporal Variability of the Blazar 3C 454.3 during 2014 Activity Phase
We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during
the high -ray active period from May-December, 2014. Except for X-rays,
the period is well sampled at near-infrared (NIR)-optical by the \emph{SMARTS}
facility and the source is detected continuously on daily timescale in the
\emph{Fermi}-LAT -ray band. The source exhibits diverse levels of
variability with many flaring/active states in the continuously sampled
-ray light curve which are also reflected in the NIR-optical light
curves and the sparsely sampled X-ray light curve by the \emph{Swift}-XRT.
Multi-band correlation analysis of this continuous segment during different
activity periods shows a change of state from no lags between IR and
-ray, optical and -ray, and IR and optical to a state where
-ray lags the IR/optical by 3 days. The results are consistent
with the previous studies of the same during various -ray flaring and
active episodes of the source. This consistency, in turn, suggests an extended
localized emission region with almost similar conditions during various
-ray activity states. On the other hand, the delay of -ray with
respect to IR/optical and a trend similar to IR/optical in X-rays along with
strong broadband correlations favor magnetic field related origin with X-ray
and -ray being inverse Comptonized of IR/optical photons and external
radiation field, respectively.Comment: 15 pages, 5 figures, 1 table, MNRAS accepte
Statistical analysis of variability properties of the Kepler blazar W2R 1926+42
We analyzed Kepler light curves of the blazar W2R 1926+42 that provided
nearly continuous coverage from quarter 11 through quarter 17 (589 days between
2011 and 2013) and examined some of their flux variability properties. We
investigate the possibility that the light curve is dominated by a large number
of individual flares and adopt exponential rise and decay models to investigate
the symmetry properties of flares. We found that those variations of W2R
1926+42 are predominantly asymmetric with weak tendencies toward positive
asymmetry (rapid rise and slow decay). The durations (D) and the amplitudes
(F0) of flares can be fit with log-normal distributions. The energy (E) of each
flare is also estimated for the first time. There are positive correlations
between logD and logE with a slope of 1.36, and between logF0 and logE with a
slope of 1.12. Lomb-Scargle periodograms are used to estimate the power
spectral density (PSD) shape. It is well described by a power law with an index
ranging between -1.1 and -1.5. The sizes of the emission regions, R, are
estimated to be in the range of 1.1*10^15 cm - 6.6*10^16 cm. The flare
asymmetry is difficult to explain by a light travel time effect but may be
caused by differences between the timescales for acceleration and dissipation
of high-energy particles in the relativistic jet. A jet-in-jet model also could
produce the observed log-normal distributions
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