Search results for "Disk"
showing 10 items of 6052 documents
Study of the reflection spectrum of the LMXB 4U 1702-429
2016
The source 4U 1702-429 (Ara X-1) is a low-mass X-ray binary system hosting a neutron star. Albeit the source is quite bright ( $\sim10^{37}$ erg s$^{-1}$) its broadband spectrum has never been studied. Neither dips nor eclipses have been observed in the light curve suggesting that its inclination angle is smaller than 60$^{\circ}$.We analysed the broadband spectrum of 4U 1702-429 in the 0.3-60 keV energy range, using XMM-Newton and INTEGRAL data, to constrain its Compton reflection component if it is present. After excluding the three time intervals in which three type-I X-ray bursts occurred, we fitted the joint XMM-Newton and INTEGRAL spectra obtained from simultaneous observations. A bro…
The Close T Tauri Binary System V4046 Sgr: Rotationally Modulated X-Ray Emission from Accretion Shocks
2012
We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotatio…
Effects of radiation in accretion regions of classical T Tauri stars
2019
Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the su…
Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
2013
(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic f…
The INTEGRAL view of the pulsating hard X-ray sky: from accreting and transitional millisecond pulsars to rotation-powered pulsars and magnetars
2020
arXiv:2012.01346v1
Gravitational Lensing: the Structure of Quasars and Galaxies
2016
We use gravitational lens systems in which a galaxy produces multiple images of a distant quasar to study the properties of both the unresolved structure of the lensed quasar and the mass distribution in the gravitational lens. First, we estimate the size and the logarithmic slope of the temperature profile in the accretion disk of the lensed quasar Q2237+0305 using a method that is independent of the component velocities, based on six epochs of multi-wavelength narrowband images from the Nordic Optical Telescope. A statistical comparison of the observed microlensing with simulations based on microlensing magnification maps gives Bayesian estimates for the half-light radius of ~8 light-days…
YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
2013
Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do not show evidence of such periodicity. Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere could disrupt the shock structure influencing the observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromosphere, taking optically thin radiation losses and thermal conduction into account. We investigated the effects of seve…
Tila, paikka ja identiteetti Helsingin sanomien asunnottomuuskeskusteluissa : diskurssianalyysi vuosien 2010-2013 artikkeleista ja mielipidekirjoituk…
2013
Tutkielman tarkoituksena on selvittää, miten tilat ja niihin liitetyt identiteetit rakentuvat asunnottomuutta koskevissa Helsingin Sanomien artikkeleissa ja mielipidekirjoituksissa 1.1.2010 ja 15.4.2013 välisellä ajalla. Koska asunnottomuutta luokitellaan sen perusteella, millaisessa fyysisessä ympäristössä asunnoton yönsä viettää, kiinnostuksen kohteena on, millaisiin ympäristöihin asunnottomuus Helsingin Sanomissa asettuu ja paikallistuu. Tutkimuksen analyysimenetelmänä on käytetty diskurssianalyysiä. Fyysiseen ympäristöön liittyvien määritelmien lisäksi tarkoituksena on hahmottaa paikkoihin ja identiteetteihin liittyvää diskursiivista todellisuutta, jolloin mielenkiinto kohdistuu niihin …
Atbildība par nelikumīgām darbībām sportā
2019
Šī darba temats ir atbildība par nelikumīgām darbībām sportā, konkrētāk, par manipulācijām ar sporta sacensībām un antidopinga noteikumu pārkāpumiem, skatoties uz faktu, ka par pirmo Krimināllikumā iekļauts atsevišķs pants, bet par dopinga lietošanu nav un kriminālatbildību iespējams piemērot tikai ļoti retos gadījumos. Tālākai tēmas analīzei būtiski izprast jēdzienu saturu, šo darbību praktisko izpausmi un ietekmi uz sportistu tiesībām, interesēm, kā arī uz sabiedrību kopumā. Bakalaura darba mērķis ir apskatīt minēto neatļauto rīcību aktualitāti Latvijā, regulējumu un tā atbilstību starptautiskajiem tiesību aktiem, kā arī regulējumu ārvalstīs, kurās par manipulācijām ar sporta sacensībām u…
Tiesneša atbildība kā instruments taisnīgas tiesas nodrošināšanai
2017
Tā kā tiesa ir vienīgā institūcija, kurai ir tiesības spriest tiesu, svarīgi, lai tiesnesis būtu taisnīgs un tiktu nodrošinātas Satversmē garantētās pamattiesības uz taisnīgu tiesu. Personai ir tiesības uz lietas likumīgu izskatīšanu, ko nodrošina tieši tiesa (tiesnesis). Gan pildot amata pienākumus, gan arī ārpus darba tiesnesim ir jāievēro likumā paredzētās normas un tiesneša ētika. Spriežot tiesu tiesnesim nedrīkst būt savas intereses un viņš ir pakļauts vienīgi likumam. Tiesnesis nes atbildību par to, lai lietas dalībnieki tiktu pie taisnīga lietas iznākuma Likuma normu pārkāpuma gadījumos, tiesnesim jānes atbildība par savu rīcību, un viņš nav no tās atbrīvots. Bakalaura darba temats i…