367 research outputs found
The connection between the radio jet and the gamma-ray emission in the radio galaxy 3C 120
We present the analysis of the radio jet evolution of the radio galaxy 3C 120
during a period of prolonged gamma-ray activity detected by the Fermi satellite
between December 2012 and October 2014. We find a clear connection between the
gamma-ray and radio emission, such that every period of gamma-ray activity is
accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new
superluminal component. However, not all ejections of components are associated
with gamma-ray events detectable by Fermi. Clear gamma-ray detections are
obtained only when components are moving in a direction closer to our line of
sight.This suggests that the observed gamma-ray emission depends not only on
the interaction of moving components with the mm-VLBI core, but also on their
orientation with respect to the observer. Timing of the gamma-ray detections
and ejection of superluminal components locate the gamma-ray production to
within almost 0.13 pc from the mm-VLBI core, which was previously estimated to
lie about 0.24 pc from the central black hole. This corresponds to about twice
the estimated extension of the broad line region, limiting the external photon
field and therefore suggesting synchrotron self Compton as the most probable
mechanism for the production of the gamma-ray emission. Alternatively, the
interaction of components with the jet sheath can provide the necessary photon
field to produced the observed gamma-rays by Compton scattering.Comment: Already accepted for publication in The Astrophysical Journa
Multiwavelength observations of the blazar BL Lacertae: a new fast TeV γ-ray flare
Proceedings of the 35th International Cosmic Ray Conference (ICRC 2017), Busan (South Korea). Published in Proceeding of Science.Observations of fast TeV γ-ray flares from blazars reveal the extreme compactness of emitting regions in blazar jets. Combined with very-long-baseline radio interferometry measurements, they probe the structure and emission mechanism of the jet. We report on a fast TeV γ-ray flare from BL Lacertae observed by VERITAS, with a rise time of about 2.3 hours and a decay time of about 36 minutes. The peak flux at >200 GeV measured with the 4-minute binned light curve is (4.2±0.6)×10−6photonsm−2s−1, or ∼180% the Crab Nebula flux. Variability in GeV γ-ray, X-ray, and optical flux, as well as in optical and radio polarization was observed around the time of the TeV γ-ray flare. A possible superluminal knot was identified in the VLBA observations at 43 GHz. The flare constrains the size of the emitting region, and is consistent with several theoretical models with stationary shocks
Freely decaying weak turbulence for sea surface gravity waves
We study numerically the generation of power laws in the framework of weak
turbulence theory for surface gravity waves in deep water. Starting from a
random wave field, we let the system evolve numerically according to the
nonlinear Euler equations for gravity waves in infinitely deep water. In
agreement with the theory of Zakharov and Filonenko, we find the formation of a
power spectrum characterized by a power law of the form of .Comment: 4 pages, 3 figure
The July 2010 outburst of the NLS1 PMN J0948+0022
We report about the multiwavelength campaign on the Narrow-Line Seyfert 1
(NLS1) Galaxy PMN J0948+0022 (z = 0.5846) performed in 2010 July-September and
triggered by high activity as measured by Fermi/LAT. The peak luminosity in the
0.1-100 GeV energy band exceeded, for the first time in this type of source,
the value of 10^48 erg/s, a level comparable to the most powerful blazars. The
comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with
that of a typical blazar - like 3C 273 - shows that the power emitted at gamma
rays is extreme.Comment: 2011 Fermi Symposium proceedings - eConf C11050
Turbulent Thermalization
We study, analytically and with lattice simulations, the decay of coherent
field oscillations and the subsequent thermalization of the resulting
stochastic classical wave-field. The problem of reheating of the Universe after
inflation constitutes our prime motivation and application of the results. We
identify three different stages of these processes. During the initial stage of
``parametric resonance'', only a small fraction of the initial inflaton energy
is transferred to fluctuations in the physically relevant case of sufficiently
large couplings. A major fraction is transfered in the prompt regime of driven
turbulence. The subsequent long stage of thermalization classifies as free
turbulence. During the turbulent stages, the evolution of particle distribution
functions is self-similar. We show that wave kinetic theory successfully
describes the late stages of our lattice calculation. Our analytical results
are general and give estimates of reheating time and temperature in terms of
coupling constants and initial inflaton amplitude.Comment: 27 pages, 13 figure
Multi-epoch parsec-scale observations of the blazar PKS 1510-089
(Abridged) We investigate the flux density variability and changes in the
parsec-scale radio structure of the flat spectrum radio quasar PKS 1510-089.
This source was target of multi-epoch VLBI and Space-VLBI observations at 4.8,
8.4 and 22 GHz carried out between 1999 and 2001. The comparison of the
parsec-scale structure observed at different epochs shows the presence of a
non-stationary jet feature moving with a superluminal apparent velocity of
16.2c+-0.7c. Over three epochs at 8.4 GHz during this period the core flux
density varies of about 50%, while the scatter in the jet flux density is
within 10%. The polarization percentage of both core and jet components
significantly change from 2 to 9 per cent, while the polarization angle of the
core shows an abrupt change of about 90 degrees becoming roughly perpendicular
to the jet direction, consistent with a change in the opacity. To complete the
picture of the physical processes at work, we complemented our observations
with multi-epoch VLBA data at 15 GHz from the MOJAVE programme spanning a time
baseline from 1995 to 2010. Since 1995 jet components are ejected roughly once
per year with the same position angle and an apparent speed between 15c and
20c, indicating that no jet precession is taking place on a timescale longer
than a decade in our frame. The variability of the total intensity flux density
together with variations in the polarization properties may be explained
assuming either a change between the optically-thick and -thin regimes produced
by a shock that varies the opacity, or a highly ordered magnetic field produced
by the compression of the relativistic plasma by a shock propagating along the
jet. Taking into account the high gamma-ray emission observed from this source
by the AGILE and Fermi satellites we investigated the connection between the
radio and gamma-ray activity during 2007-2010.Comment: 12 pages, 13 figures; accepted for publication in MNRA
Benign breast tumors and risk factors for their development
The purpose of the review was to evaluate and analyze the literature data on the presented problem in recent years.Цель обзора – оценка и анализ литературных данных по представленной проблеме за последние годы
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