Search results for "astronomy & astrophysics"
showing 10 items of 1148 documents
The history of chemical enrichment in the intracluster medium from cosmological simulations
2017
The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analyzing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the SPH GADGET-3 code, have been run including two different sets of baryonic physics: one accounts for radiative coolin…
VLBI detection of the HST-1 feature in the M87 jet at 2 cm
2010
A bright feature 80 pc away from the core in the powerful jet of M87 shows highly unusual properties. Earlier radio, optical and X-ray observations have shown that this feature, labeled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. It has been claimed that this feature might have a blazar nature, due to these properties. To examine the possible blazar-like nature of HST-1, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs obtained between 2000 and 2009. Applying VLBI wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolution. Here …
Coupling hydrodynamics and radiation calculations for star-jet interactions in active galactic nuclei
2016
Context. Stars and their winds can contribute to the non-thermal emission in extragalactic jets. Because of the complexity of jet-star interactions, the properties of the resulting emission are closely linked to those of the emitting flows. Aims. We simulate the interaction between a stellar wind and a relativistic extragalactic jet and use the hydrodynamic results to compute the non-thermal emission under different conditions. Methods. We performed relativistic axisymmetric hydrodynamical simulations of a relativistic jet interacting with a supersonic, non-relativistic stellar wind. We computed the corresponding streamlines out of the simulation results and calculated the injection, evolut…
Jet-torus connection in radio galaxies
2017
High-resolution Very-Long-Baseline Interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jet, could be induced by the different conditions in the surrounding ambient medium including the obscuring torus, or a combination of the two. In this paper we investigate the influence of the ambient medium (including the obscuring torus) on the observed properties of jets from radio galaxies. We performed special-relativistic hydrodynamic (RHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code \texttt{Ratpenat}…
Correlation of the highest-energy cosmic rays with nearby extragalactic objects.
2007
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above ~ 6x10^{19} electron volts and the positions of active galactic nuclei (AGN) lying within ~ 75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar…
Long-term monitoring of mrk 501 for its very high energy γ emission and a flare in 2011 october
2012
"As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, is very useful for" "physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitored Mrk 501 for γ - rays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ -ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ -ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady…
Dissipative Processes and Their Role in the Evolution of Radio Galaxies
2019
Particle acceleration in relativistic jets to very high energies occurs at the expense of the dissipation of magnetic or kinetic energy. Therefore, understanding the processes that can trigger this dissipation is key to the characterization of the energy budgets and particle acceleration mechanisms at action in active galaxies. Instabilities and entrainment are two obvious candidates to trigger dissipation. On the one hand, supersonic, relativistic flows threaded by helical fields, as expected from the standard formation models of jets in supermassive black-holes, are unstable to a series of magnetohydrodynamical instabilities, such as the Kelvin-Helmholtz, current-driven, or possibly the p…
Secondary School Students' Knowledge and Opinions on Astrobiology Topics and Related Social Issues.
2017
Astrobiology is the study of the origin of life on Earth and the distribution of life in the Universe. Its multidisciplinary approach, social and philosophical implications, and appeal within the discipline and beyond make astrobiology a uniquely qualified subject for general science education. In this study, student knowledge and opinions on astrobiology topics were investigated. Eighty-nine students in their last year of compulsory education (age 15) completed a written questionnaire that consisted of 10 open questions on the topic of astrobiology. The results indicate that students have significant difficulties understanding the origin of life on Earth, despite exposure to the topic by w…
A study of the effect of molecular and aerosol conditions in the atmosphere on air fluorescence measurements at the Pierre Auger Observatory
2010
The air fluorescence detector of the Pierre Auger Observatory is designed to perforin calorimetric measurements of extensive air showers created by Cosmic rays of above 10(18) eV. To correct these measurements for the effects introduced by atmospheric fluctuations, the Observatory contains a group Of monitoring instruments to record atmospheric conditions across the detector site, ail area exceeding 3000 km(2). The atmospheric data are used extensively in the reconstruction of air showers, and are particularly important for the correct determination of shower energies and the depths of shower maxima. This paper contains a summary of the molecular and aerosol conditions measured at the Pierr…
Optical and ultraviolet pulsed emission from an accreting millisecond pulsar
2021
Ambrosino, F., et al.