384 research outputs found
Frequency dependent core shifts and parameter estimation for the blazar 3C 454.3
We study the core shift effect in the parsec scale jet of the blazar 3C 454.3
using the 4.8 GHz - 36.8 GHz radio light curves obtained from three decades of
continuous monitoring. From a piecewise Gaussian fit to each flare, time lags
between the observation frequencies and spectral indices
based on peak amplitudes are determined. From the fit , indicating equipartition between
the magnetic field energy density and the particle energy density. From the fit
, is in the range to . A mean
magnetic field strength at 1 pc, G, and at the core,
mG, are inferred, consistent with previous
estimates. The measure of core position offset is
pc GHz when averaged over all frequency pairs. Based on the
statistical trend shown by the measured core radius as a
function of , we infer that the synchrotron opacity model may not be valid
for all cases. A Fourier periodogram analysis yields power law slopes in the
range to describing the power spectral density shape and gives
bend timescales in the range yr. This result, and both positive
and negative , indicate that the flares originate from multiple shocks
in a small region. Important objectives met in our study include: the
demonstration of the computational efficiency and statistical basis of the
piecewise Gaussian fit; consistency with previously reported results; evidence
for the core shift dependence on observation frequency and its utility in jet
diagnostics in the region close to the resolving limit of very long baseline
interferometry observations.Comment: 12 pages, 11 figures (23 sub-figures), 5 tables. Accepted for
publication in MNRA
Chandra and HST observations of gamma-ray blazars: comparing jet emission at small and large scales
We present new Chandra and HST data for four gamma-ray blazars selected on
the basis of radio morphology with the aim of revealing X-ray and optical
emission from their jets at large scales. All the sources have been detected.
Spectral Energy Distributions of the large scale jets are obtained as well as
new X-ray spectra for the blazar cores. Modeling for each object the core
(sub-pc scale) and large-scale (>100 kpc) jet SEDs, we derive the properties of
the same jet at the two scales. The comparison of speeds and powers at
different scales supports a simple scenario for the dynamics and propagation of
high power relativistic jets.Comment: Accepted for publication in Ap
Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies
We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that
were previously classified as radio silent and two that were classified as
radio quiet. These detections reveal the presumption that NLS1 galaxies
labelled radio quiet or radio silent and hosted by spiral galaxies are unable
to launch jets to be incorrect. The detections are a plausible indicator of the
presence of a powerful, most likely relativistic jet because this intensity of
emission at 37 GHz cannot be explained by, for example, radiation from
supernova remnants. Additionally, one of the detected NLS1 galaxies is a newly
discovered source of gamma rays and three others are candidates for future
detections.Comment: 5 pages, 1 figure, 37 GHz data available in electronic form at the
CDS. Accepted in A&
37 GHz observations of narrow-line Seyfert 1 galaxies
Observations at 37 GHz, performed at Mets\"ahovi Radio Observatory, are
presented for a sample of 78 radio-loud and radio-quiet narrow-line Seyfert 1
(NLS1) galaxies, together with additional lower and higher frequency radio data
from RATAN-600, Owens Valley Radio Observatory, and the Planck satellite. Most
of the data have been gathered between February 2012 and April 2015 but for
some sources even longer lightcurves exist. The detection rate at 37 GHz is
around 19%, comparable to other populations of active galactic nuclei presumed
to be faint at radio frequencies, such as BL Lac objects. Variability and
spectral indices are determined for sources with enough detections. Based on
the radio data, many NLS1 galaxies show a blazar-like radio spectra exhibiting
significant variability. The spectra at a given time are often inverted or
convex. The source of the high-frequency radio emission in NLS1 galaxies,
detected at 37 GHz, is most probably a relativistic jet rather than star
formation. Jets in NLS1 galaxies are therefore expected to be a much more
common phenomenon than earlier assumed.Comment: Accepted for publication in A&A. Table of 37 GHz data will be
available at the CDS soo
An Optical Survey of the Position Error Contours of Unidentified High Energy Gamma-Ray Sources at Galactic Latitude b >|20| degrees
We present the most recent results of an optical survey of the position error
contours ("error boxes") of unidentified high energy gamma-ray sources.Comment: 1 figure, 3 tables, to be published in Astronomical Journa
30 years of multi-wavelength observations of 3C 273
We present a wide multi-wavelength database of most observations of the
quasar 3C 273 obtained during the last 30 years. This database is the most
complete set of observations available for an active galactic nucleus (AGN). It
contains nearly 20'000 observations grouped together into 70 light curves
covering 16 orders of magnitude in frequency from the radio to the gamma-ray
domain.
The database is constituted of many previously unpublished observations and
of most publicly available data gathered in the literature and on the World
Wide Web (WWW). It is complete to the best of our knowledge, except in the
optical (UBV) domain where we chose not to add all observations from the
literature. In addition to the photometric data, we present the spectra of 3C
273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the
X-ray domain, we used the spectral fit parameters from the literature to
construct the light curves.
Apart from describing the data, we show the most representative light curves
and the average spectrum of 3C 273. The database is available on the WWW in a
homogeneous and clear form and we wish to update it regularly by adding new
observations.Comment: 12 pages, 6 figures, to be published in A&AS, data available at:
http://obswww.unige.ch/3c273
Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007
Since the CGRO operation in 1991-2000, one of the primary unresolved
questions about the blazar gamma-ray emission has been its possible correlation
with the low-energy (in particular optical) emission. To help answer this
problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the
GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring
data to be compared with the gamma-ray detections by the AGILE and GLAST
satellites. This new WEBT project started in early September 2007, just before
a strong gamma-ray detection of 0716+714 by AGILE. We present the GASP-WEBT
optical and radio light curves of this blazar obtained in July-November 2007,
about various AGILE pointings at the source. We construct NIR-to-UV spectral
energy distributions (SEDs), by assembling GASP-WEBT data together with UV data
from the Swift ToO observations of late October. We observe a contemporaneous
optical-radio outburst, which is a rare and interesting phenomenon in blazars.
The shape of the SEDs during the outburst appears peculiarly wavy because of an
optical excess and a UV drop-and-rise. The optical light curve is well sampled
during the AGILE pointings, showing prominent and sharp flares. A future
cross-correlation analysis of the optical and AGILE data will shed light on the
expected relationship between these flares and the gamma-ray events.Comment: 5 pages, 5 figures, to be published in A&A (Letters); revised to
match the final version (changes in Fig. 5 and related text
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