73 research outputs found
Nine years of multi-frequency monitoring of the blazar PKS 0048-097: spectral and temporal variability
Blazars are highly variable, radio-loud active galactic nuclei with jets
oriented at a small angle to the line of sight. The observed emission of these
sources covers the whole electromagnetic spectrum from radio frequencies up to
the high or even very high energy gamma-ray range. To understand the complex
physics of these objects, multi-wavelength observations and studies on the
variability and correlations between different wavelengths are therefore
essential. The long-term multi-frequency observations of PKS 0048-097 are
analysed here to investigate its spectral and temporal features. The studies
includes nine years of observations of the blazar, which is well studied in the
optical and radio domain, but not in the other frequencies. Multi-wavelength
data collected with OVRO, KAIT, Catalina, Swift/UVOT, Swift/XRT and Fermi/LAT
were studied. The performed analysis revealed strong variability in all
wavelengths that is most clearly manifested in the X-ray range. The correlation
studies do not exhibit any relation between different wavelengths, except for
the very strong positive correlation between the optical emission in V and R
bands.Comment: 11 pages, 7 figures, published in A&
Signature of Inverse Compton emission from blazars
Blazars are classified into high, intermediate and low energy peaked sources
based on the location of their synchrotron peak. This lies in infra-red/optical
to ultra-violet bands for low and intermediate peaked blazars. The transition
from synchrotron to inverse Compton emission falls in the X-ray bands for such
sources. We present the spectral and timing analysis of 14 low and intermediate
energy peaked blazars ob- served with XMMNewton spanning 31 epochs. Parametric
fits to X-ray spectra helps constrain the possible location of transition from
the high energy end of the syn- chrotron to the low energy end of the inverse
Compton emission. In seven sources in our sample, we infer such a transition
and constrain the break energy in the range 0.6 10 keV. The Lomb-Scargle
periodogram is used to estimate the power spectral density (PSD) shape. It is
well described by a power law in a majority of light curves, the index being
flatter compared to general expectation from AGN, ranging here between 0.01 and
1.12, possibly due to short observation durations resulting in an absence of
long term trends. A toy model involving synchrotron self-Compton (SSC) and
exter- nal Compton (EC; disk, broad line region, torus) mechanisms are used to
estimate magnetic field strength 6 0.03 - 0.88 G in sources displaying the
energy break and infer a prominent EC contribution. The timescale for
variability being shorter than synchrotron cooling implies steeper PSD slopes
which are inferred in these sources.Comment: 24 pages, 6 Tables, 13 figures, Accepted for MNRA
Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations
Blazars are the established sources of an intense and variable non-thermal
radiation extending from radio wavelengths up to HE and VHE gamma-rays.
Understanding the spectral evolution of blazars in selected frequency ranges,
as well as multi-frequency correlations in various types of blazar sources, is
of a primary importance for constraining the blazar physics. Here we present
the results of a long-term optical monitoring of a sample of 30 blazars of the
BL Lac type. We study the optical color-magnitude correlation patterns emerging
in the analyzed sample, and compare the optical properties of the targets with
the high-energy gamma-ray and high-frequency radio data. The optical
observations were carried out in R and B filters using ATOM telescope. Each
object was observed during at least 20 nights in the period 2007-2012. We find
significant global color-magnitude correlations in 40 % of the sample. The
sources which do not display any clear chromatism often do exhibit
bluer-when-brighter (bwb) behavior but only in isolated shorter time intervals.
We also discovered spectral state transitions at optical wavelengths in several
sources. Finally, we find that the radio, optical, and gamma-ray luminosities
of the sources obey almost linear correlations, which seem however induced, at
least partly, by the redshift dependance, and may be also affected by
non-simultaneousness of the analyzed dataset. We argue that the observed bwb
behavior is intrinsic to the jet emission regions, at least for some of the
analyzed blazars, rather than resulting from the contamination of the measured
flux by the starlight of host galaxies. We also conclude that the significance
of color-magnitude scalings does not correlate with the optical color, but
instead seems to depend on the source luminosity, in a sense that these are the
lowest-luminosity BL Lac objects which display the strongest correlations.Comment: 16 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
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