19 research outputs found
Multifrequency VLBA study of the blazar S5 0716+714 during the active state in 2004 II. Large-scale jet kinematics and the comparison of the different methods of VLBI data imaging as applied to kinematic studies of AGN
We study the jet kinematics of the blazar S5 0716+714 during its active state
in 2003-2004 with multi-epoch VLBI observations. Aims. We present a kinematic
analysis of the large-scale (0-12 mas) jet of 0716+714, based on the results of
six epochs of VLBA monitoring at 5 GHz. Additionally, we compare kinematic
results obtained with two imaging methods based on different deconvolution
algorithms. The blazar 0716+714 has a diffuse large-scale jet and a very faint
bright compact core. Experiments with simulated data showed that the
conventional data reduction procedure based on the CLEAN deconvolution
algorithm does not perform well in restoring this type of structure. This might
be the reason why previous kinematic studies of this source yielded ambiguous
results. In order to obtain accurate kinematics of this source, we
independently applied two imaging techniques to the raw data: the conventional
method, based on difference mapping, which uses CLEAN deconvolution, and the
generalized maximum entropy method (GMEM) realized in the VLBImager package
developed at the Pulkovo Observatory in Russia. The results of both methods
give us a consistent kinematic scenario: the large-scale jet of 0716+714 is
diffuse and stationary. Differences between the inner (0-1 mas) and outer (1-12
mas) regions of the jet in brightness and velocity of the components could be
explained by the bending of the jet, which causes the angle between the jet
direction and the line of sight to change from ~5 deg to ~11 deg. For the
source 0716+714 both methods worked at the limit of their capability.Comment: 13 pages, 7 figures. Accepted for publication in A&A, 201
A multi-wavelength polarimetric study of the blazar CTA 102 during a Gamma-ray flare in 2012
We perform a multi-wavelength polarimetric study of the quasar CTA 102 during
an extraordinarily bright -ray outburst detected by the {\it Fermi}
Large Area Telescope in September-October 2012 when the source reached a flux
of F photons cm s.
At the same time the source displayed an unprecedented optical and NIR
outburst. We study the evolution of the parsec scale jet with ultra-high
angular resolution through a sequence of 80 total and polarized intensity Very
Long Baseline Array images at 43 GHz, covering the observing period from June
2007 to June 2014. We find that the -ray outburst is coincident with
flares at all the other frequencies and is related to the passage of a new
superluminal knot through the radio core. The powerful -ray emission is
associated with a change in direction of the jet, which became oriented more
closely to our line of sight (1.2) during the ejection of
the knot and the -ray outburst. During the flare, the optical polarized
emission displays intra-day variability and a clear clockwise rotation of
EVPAs, which we associate with the path followed by the knot as it moves along
helical magnetic field lines, although a random walk of the EVPA caused by a
turbulent magnetic field cannot be ruled out. We locate the -ray
outburst a short distance downstream of the radio core, parsecs from the black
hole. This suggests that synchrotron self-Compton scattering of near-infrared
to ultraviolet photons is the probable mechanism for the -ray
production.Comment: Accepted for publication in The Astrophysical Journa
Multiwavelength Intraday Variability of the BL Lac S5 0716+714
We report results from a 1 week multi-wavelength campaign to monitor the BL
Lac object S5 0716+714 (on December 9-16, 2009). In the radio bands the source
shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up
to ~ 10 %. The variability at 2.8 cm leads by about 1 day the variability at 6
cm and 11 cm. This time lag and more rapid variations suggests an intrinsic
contribution to the source's intraday variability at 2.8 cm, while at 6 cm and
11 cm interstellar scintillation (ISS) seems to predominate. Large and
quasi-sinusoidal variations of ~ 0.8 mag were detected in the V, R and I-bands.
The X-ray data (0.2-10 keV) do not reveal significant variability on a 4 day
time scale, favoring reprocessed inverse-Compton over synchrotron radiation in
this band. The characteristic variability time scales in radio and optical
bands are similar. A quasi-periodic variation (QPO) of 0.9 - 1.1 days in the
optical data may be present, but if so it is marginal and limited to 2.2
cycles. Cross-correlations between radio and optical are discussed. The lack of
a strong radio-optical correlation indicates different physical causes of
variability (ISS at long radio wavelengths, source intrinsic origin in the
optical), and is consistent with a high jet opacity and a compact synchrotron
component peaking at ~= 100 GHz in an ongoing very prominent flux density
outburst. For the campaign period, we construct a quasi-simultaneous spectral
energy distribution (SED), including gamma-ray data from the FERMI satellite.
We obtain lower limits for the relativistic Doppler-boosting of delta >= 12-26,
which for a BL\,Lac type object, is remarkably high.Comment: 16 pages, 15 figures, table 2; Accepted for Publication in MNRA
VizieR Online Data Catalog: 1Jy northern AGN sample (Planck+, 2016)
The complete sample presented in this paper consists of 104 northern and equatorial radio-loud AGN. It includes all AGN with declination >=-10° that have a measured average radio flux density at 37GHz exceeding 1Jy. Most of the sample sources have been monitored at Metsahovi Radio Observatory for many years, and the brightest sources have been observed for up to 30yr. (1 data file)
Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
Context. 1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E > 100 GeV) gamma rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED). Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum.Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsahovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE.Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 +/- 0.22 and a flux above 150 GeV of (1.46 +/- 0.16) x 10(-11) ph cm(-2) s(-1). The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 +/- 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac.Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission
Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
Context. 1ESâ1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100âGeV) Îł rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED).
Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum.
Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and MetsÀhovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE.
Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150âGeV of (1.46 ± 0.16) Ă 10-11âphâcm-2âs-1. The source 1ESâ1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac.
Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1âGeV to 1âTeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission
Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
Context. 1ESâ1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100âGeV) Îł rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED).
Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum.
Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and MetsÀhovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE.
Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150âGeV of (1.46 ± 0.16) Ă 10-11âphâcm-2âs-1. The source 1ESâ1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac.
Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1âGeV to 1âTeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission