Search results for "lazar"
showing 10 items of 91 documents
ANTARES constrains a blazar origin of two IceCube PeV neutrino events
2015
Abstract Context. The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally coincident with two of the most energetic IceCube events. Objects like these are prime candidates to be the source of the highest-energy cosmic rays, and thus of associated neutrino emission. Aims. We present an analysis of neutrino emission from the six blazars using observations with the ANTARES neutrino telescope. Methods. The standard methods of the ANTARES candidate list search are applied to six years of data to search for an excess of muons and hence th…
Gamma-Ray Flares from Mrk421 in 2008 observed with the ARGO-YBJ detector
2010
In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6) 10^-1…
ALMA full polarization observations of PKS1830-211 during its record-breaking flare of 2019
2020
We report Atacama Large Millimeter Array (ALMA) Band 6 full-polarization observations of the lensed blazar PKS 1830-211 during its record-breaking radio and gamma-ray flare in the spring of 2019. The observations were taken close to the peak of the gamma activity and show a clear difference in polarization state between the two time-delayed images. The leading image has a fractional polarization about three times lower than the trailing image, implying that significant depolarization occurred during the flare. In addition, we observe clear intra-hour variability of the polarization properties between the two lensed images, with a quasi-linear increase in the differential electric-vector pos…
Relativistic beaming and gamma-ray brightness of blazars
2009
We investigate the dependence of gamma-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. By combining apparent jet speeds derived from high-resolution VLBA images from the MOJAVE program with millimetre-wavelength flux density monitoring data from Metsahovi Radio Observatory, we estimate the jet Doppler factors, Lorentz factors, and viewing angles for a sample of 62 blazars. We study the trends in these quantities between the sources which were detected in gamma-rays by the Fermi Large Area Telescope (LAT) during its first three months of science operations and those which were not detected. The LAT-detected blaz…
High-Frequency Polarization Variability from Active Galactic Nuclei
2021
The linear polarization of non-thermal emission encodes information about the structure of the magnetic fields, either from the region where the emission is produced (i.e., the intrinsic polarization angle) and/or from the screens of magnetized plasma that may be located on its way towards Earth (i.e., the effect of Faraday rotation). In addition, the variability timescale of the polarized emission, or its Faraday rotation, can be used to estimate the size of the region where the emission (or the Faraday rotation) originates. The observation of polarized emission from active galactic nuclei (AGN) and, in particular, its time evolution, also provides information about the critical role that …
Integrismo político en EEUU / 2. Integrismo y tortura
2004
MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VI. Kinematics Analysis of a Complete Sample of Blazar Jets
2009
We discuss the jet kinematics of a complete flux-density-limited sample of 135 radio-loud active galactic nuclei (AGN) resulting from a 13 year program to investigate the structure and evolution of parsec-scale jet phenomena. Our analysis is based on new 2 cm Very Long Baseline Array (VLBA) images obtained between 2002 and 2007, but includes our previously published observations made at the same wavelength, and is supplemented by VLBA archive data. In all, we have used 2424 images spanning the years 1994-2007 to study and determine the motions of 526 separate jet features in 127 jets. The data quality and temporal coverage (a median of 15 epochs per source) of this complete AGN jet sample r…
El ejército portugués dio paso a la democracia 25 de Abril en Portugal
1999
Soportes de la lucha para la democracia
1996
Notas de José Vidal-Beneyto para un discurso dado en el Centro Nacional de Cultura de Lisboa en octubre 1996.
De la dictadura a la democracia pasando por la revolución
1999
Se trata del texto de una conferencia de José Vidal-Beneyto. Se desconoce en qué espacio y contexto fue pronunciada y aqunque aquí se recoge la versión mecanografiada por el propio autor, existe una versión publicada en: Vidal-Beneyto, José (2007). Memoria democrática (pp. 149-154). Madrid: Foca.