115 research outputs found
About H-models Of Noninertial System
In this paper we consider the problem of modeling noninertial processes with stochastic dependence between the input variables. Such processes are called H-processes ("tubular" structure processes). A new class of parametric identification algorithms with the indicator function of multidimensional static objects is suggested to use. The results of some computational experiments are presented
Analysis of the intra-night variability of BL Lacertae during its August 2020 flare
We present an analysis of the photometry of the blazar BL Lacertae on
diverse timescales from mid-July to mid-September 2020. We have used 11
different optical telescopes around the world and have collected data over 84
observational nights. The observations cover the onset of a new activity phase
of BL Lacertae started in August 2020 (termed as the August 2020 flare by us),
and the analysis is focused on the intra-night variability. On short-term
timescales, (i) flux varied with ~2.2\,mag in band, (ii) the spectral index
was found to be weakly dependent on the flux (i.e., the variations could be
considered mildly chromatic) and (iii) no periodicity was detected. On
intra-night timescales, BL Lacertae was found to show bluer-when-brighter
chromatism predominantly. We also found two cases of significant inter-band
time lags of the order of a few minutes. The duty cycle of the blazar during
the August 2020 flare was estimated to be quite high (~90\% or higher). We
decomposed the intra-night light curves into individual flares and determined
their characteristics. On the basis of our analysis and assuming the turbulent
jet model, we determined some characteristics of the emitting regions: Doppler
factor, magnetic field strength, electron Lorentz factor, and radius. The radii
determined were discussed in the framework of the Kolmogorov theory of
turbulence. We also estimated the weighted mean structure function slope on
intra-night timescales, related it to the slope of the power spectral density,
and discussed it with regard to the origin of intra-night variability.Comment: 46 pages, 19 figures, 8 tables, accepted for publication in The
Astrophysical Journal Supplement Series (manuscript version after proof
correction
Duality for the Jordanian Matrix Quantum Group
We find the Hopf algebra dual to the Jordanian matrix quantum group
. As an algebra it depends only on the sum of the two parameters
and is split in two subalgebras: (with three generators) and
(with one generator). The subalgebra is a central Hopf subalgebra of
. The subalgebra is not a Hopf subalgebra and its coalgebra
structure depends on both parameters. We discuss also two one-parameter special
cases: and . The subalgebra is a Hopf algebra and
coincides with the algebra introduced by Ohn as the dual of . The
subalgebra is isomorphic to as an algebra but has a
nontrivial coalgebra structure and again is not a Hopf subalgebra of
.Comment: plain TeX with harvmac, 16 pages, added Appendix implementing the ACC
nonlinear ma
Duality for Exotic Bialgebras
In the classification of Hietarinta, three triangular
-matrices lead, via the FRT formalism, to matrix bialgebras which are not
deformations of the trivial one. In this paper, we find the bialgebras which
are in duality with these three exotic matrix bialgebras. We note that the
duality of FRT is not sufficient for the construction of the bialgebras
in duality. We find also the quantum planes corresponding to these bialgebras
both by the Wess-Zumino R-matrix method and by Manin's method.Comment: 25 pages, LaTeX2e, using packages: cite, amsfonts, amsmath, subeq
Dissecting the long-term emission behaviour of the BL Lac object Mrk 421
We report on long-term multiwavelengthmonitoring of blazar Mrk 421 by the GLAST-AGILE
Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and
Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in
the period 2007–2015, characterized by several extreme flares. The ratio between the optical,
X-ray and γ -ray fluxes is very variable. The γ -ray flux variations show a fair correlation with
the optical ones starting from 2012.We analyse spectropolarimetric data and find wavelengthdependence
of the polarization degree (P), which is compatible with the presence of the
host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA).
Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of
the EVPA.We build broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite.
They show strong variability in both flux and X-ray spectral shape and suggest a shift of
the synchrotron peak up to a factor of ∼50 in frequency. The interpretation of the flux and
spectral variability is compatible with jet models including at least two emitting regions that
can change their orientation with respect to the line of sight.http://10.0.4.69/mnras/stx2185Accepted manuscrip
A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008
We present and analyse the WEBT multifrequency observations of 3C 454.3 in
the 2007-2008 observing season, including XMM-Newton observations and near-IR
spectroscopic monitoring, and compare the recent emission behaviour with the
past one. In the optical band we observed a multi-peak outburst in July-August
2007, and other faster events in November 2007 - February 2008. During these
outburst phases, several episodes of intranight variability were detected. A mm
outburst was observed starting from mid 2007, whose rising phase was
contemporaneous to the optical brightening. A slower flux increase also
affected the higher radio frequencies, the flux enhancement disappearing below
8 GHz. The analysis of the optical-radio correlation and time delays, as well
as the behaviour of the mm light curve, confirm our previous predictions,
suggesting that changes in the jet orientation likely occurred in the last few
years. The historical multiwavelength behaviour indicates that a significant
variation in the viewing angle may have happened around year 2000. Colour
analysis reveals a complex spectral behaviour, which is due to the interplay of
different emission components. All the near-IR spectra show a prominent Halpha
emission line, whose flux appears nearly constant. The analysis of the
XMM-Newton data indicates a correlation between the UV excess and the
soft-X-ray excess, which may represent the head and the tail of the big blue
bump, respectively. The X-ray flux correlates with the optical flux, suggesting
that in the inverse-Compton process either the seed photons are synchrotron
photons at IR-optical frequencies or the relativistic electrons are those that
produce the optical synchrotron emission. The X-ray radiation would thus be
produced in the jet region from where the IR-optical emission comes.Comment: 10 pages, 12 figures (7 included in the text, 5 in GIF format),
accepted for publication in A&
WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth
Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the
XMM-Newton satellite, to study its emission properties. The source was
monitored in the optical-to-radio bands by 37 telescopes. The brightness level
was relatively low. Some episodes of very fast variability were detected in the
optical bands. The X-ray spectra are well fitted by a power law with photon
index of about 2 and photoelectric absorption exceeding the Galactic value.
However, when taking into account the presence of a molecular cloud on the line
of sight, the data are best fitted by a double power law, implying a concave
X-ray spectrum. The spectral energy distributions (SEDs) built with
simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations
suggest that the peak of the synchrotron emission lies in the near-IR band, and
show a prominent UV excess, besides a slight soft-X-ray excess. A comparison
with the SEDs corresponding to previous observations with X-ray satellites
shows that the X-ray spectrum is extremely variable. We ascribe the UV excess
to thermal emission from the accretion disc, and the other broad-band spectral
features to the presence of two synchrotron components, with their related SSC
emission. We fit the thermal emission with a black body law and the non-thermal
components by means of a helical jet model. The fit indicates a disc
temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s.Comment: 11 pages, 7 figures, accepted for publication in A&
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