373 research outputs found
Fermi-LAT Observation of Non-Blazar AGNs
We report on a detailed investigation of the -ray emission from 26
non-blazar AGNs based on the Fermi LAT data accumulated for 7 years. The photon
index of non-blazar AGNs changes in the range of 1.84-2.86 and the flux varies
from a few times to . Over long time periods, power-law provides an adequate
description of the -ray spectra of almost all sources. Significant
curvature is observed in the -ray spectra of NGC 1275, NGC 6251, SBS
0846+513 and PMN J0948+0022 and their spectra are better described by
log-parabola or power-law with exponential cut-off models. The -ray
spectra of PKS 0625-25 and 3C 380 show a possible deviation from a simple
power-law shape, indicating a spectral cutoff around the observed photon energy
of GeV and GeV, respectively.
Our analysis confirms the previous finding of an unusual spectral turnover in
the -ray spectrum of Cen A: the photon index changes from
to at GeV. In the plane, the
luminosity of non-blazar AGNs is spread in the range of , where the lowest luminosity have FRI radio galaxies (but
typically appear with a harder photon index) and the highest- SSRQs/NLSY1s
(with softer photon indexes). We confirm the previously reported
short-timescale flux variability of NGC 1275 and 3C 120. The -ray
emission from NLSY1s, 1H 0323+342, SBS 0846+513 and PMN J0948+0022, is
variable, showing flares in short scales sometimes accompanied by a moderate
hardening of their spectra (e.g., on MJD 56146.8 the -ray photon index
of SBS 0846+513 was ). 3C 111, Cen A core, 3C 207, 3C 275.1, 3C
380, 4C+39.23B, PKS 1502+036 and PKS 2004-447 show a long-timescale flux
variability in the -ray band.Comment: Accepted for publication in Astronomy & Astrophysics. The abstract
has been shortened to comply with the size limit set by arXi
Comparing 3C 120 jet emission at small and large scales
Context. Important information on the evolution of the jet can be obtained by
comparing the physical state of the plasma at its propagation through the
broad-line region (where the jet is most likely formed) into the intergalactic
medium, where it starts to significantly decelerate. Aims. We compare the
constraints on the physical parameters in the innermost ( pc) and outer
( kpc) regions of the 3C 120 jet by means of a detailed multiwavelength
analysis and theoretical modeling of their broadband spectra. Methods.The data
collected by Fermi LAT, Swift and Chandra are analyzed together and the
spectral energy distributions are modeled using a leptonic synchrotron and
inverse Compton model, taking into account the seed photons originating inside
and outside of the jet. The model parameters are estimated using the MCMC
method. Results. The -ray flux from the inner jet of 3C 120 was
characterized by rapid variation from MJD 56900 to MJD 57300. Two strong flares
were observed on April 24, 2015 when, within 19.0 minutes and 3.15 hours the
flux was as high as and
respectively. The broadband
emission in the quiet and flaring states can be described as SSC emission while
IC scattering of dusty torus photons cannot be excluded for the flaring states.
The X-ray emission from the knots can be well reproduced by IC scattering of
CMB photons only if the jet is highly relativistic (since even when
still ). These extreme requirements can be somewhat
softened assuming the X-rays are from the synchrotron emission of a second
population of very-high-energy electrons. Conclusions. We found that the jet
power estimated at two scales is consistent, suggesting that the jet does not
suffer severe dissipation, it simply becomes radiatively inefficient.Comment: Accepted for publication in Astronomy & Astrophysics. The abstract
has been shortened to comply with the size limit set by arXi
Gradient boosting decision trees classification of blazars of uncertain type in the fourth Fermi-LAT catalog
The deepest all-sky survey available in the -ray band - the last
release of the Fermi-LAT catalogue (4FGL-DR3) based on the data accumulated in
12 years, contains more than 6600 sources. The largest population among the
sources is blazar subclass - 3743, of which are classified as BL
Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the
rest are listed as blazar candidates of uncertain type (BCU) as their firm
optical classification is lacking. The goal of this study is to classify BCUs
using different machine learning algorithms which are trained on the spectral
and temporal properties of already classified BL Lacs and FSRQs. Artificial
Neural Networks, \textit{XGBoost} and LightGBM algorithms are employed to
construct predictive models for BCU classification. Using 18 input parameters
of 2219 BL Lacs and FSRQs, we train (80\% of the sample) and test (20\%) these
algorithms and find that LightGBM model, state-of-the-art classification
algorithm based on gradient boosting decision trees, provides the highest
performance. Based on our best model, we classify 825 BCUs as BL Lac candidates
and 405 as FSRQ candidates, however, 190 remain without a clear prediction but
the percentage of BCUs in 4FGL is reduced to 5.1\%. The -ray photon
index, synchrotron peak frequency, and high energy peak frequency of a large
sample are used to investigate the relationship between FSRQs and BL Lacs
(LBLs, IBLs, and HBLs).Comment: Accepted for publication in MNRA
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