Search results for "disks"
showing 8 items of 118 documents
Observatory science with eXTP
2019
Disponible preprint en: arXiv:1812.04023v1 [astro-ph.HE] [v1] Mon, 10 Dec 2018 19:00:52 UTC (4,376 KB)
Sobolev homeomorphic extensions onto John domains
2020
Given the planar unit disk as the source and a Jordan domain as the target, we study the problem of extending a given boundary homeomorphism as a Sobolev homeomorphism. For general targets, this Sobolev variant of the classical Jordan-Schoenflies theorem may admit no solution - it is possible to have a boundary homeomorphism which admits a continuous $W^{1,2}$-extension but not even a homeomorphic $W^{1,1}$-extension. We prove that if the target is assumed to be a John disk, then any boundary homeomorphism from the unit circle admits a Sobolev homeomorphic extension for all exponents $p<2$. John disks, being one sided quasidisks, are of fundamental importance in Geometric Function Theory.
High-energy monitoring of NGC 4593 II. Broad-band spectral analysis: testing the two-corona model
2019
It is widely believed that the primary X-ray emission of AGN is due to the Comptonisation of optical-UV photons from a hot electron corona, while the origin of the 'soft-excess' is still uncertain and matter of debate. A second Comptonisation component, called warm corona, was therefore proposed to account for the soft-excess, and found in agreement with the optical-UV to X-ray emission of a sample of Seyfert galaxies. In this context, we exploit the broadband XMM-Newton and NuSTAR simultaneous observations of the Seyfert galaxy NGC 4593 to further test the so called "two corona model". The NGC 4593 spectra are well reproduced by the model, from the optical/UV to the hard X-rays. Moreover, …
Broad-band Spectral Evolution of Scorpius X-1 along its Color-Color Diagram
2007
We analyze a large collection of RXTE archive data from April 1997 to August 2003 of the bright X-ray source Scorpius X-1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by studying energy spectra from selected regions in the Z-track of its Color-Color Diagram. A two-component model, consisting of a soft thermal component interpreted as thermal emission from an accretion disk and a thermal Comptonization component, is unable to fit the whole 3--200 keV energy spectrum at low accretion rates. Strong residuals in the highest energy band of the spectrum require the addition of a third component that can be fitted with a …
Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
2006
We performed a timing analysis of the fastest accreting millisecond pulsar IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We corrected the arrival times of all the events for the orbital (Doppler) effects and performed a timing analysis of the resulting phase delays. In this way we have the possibility to study, for the first time in this class of sources, the spin-up of a millisecond pulsar as a consequence of accretion torques during the X-ray outburst. The accretion torque gives us for the first time an independent estimate of the mass accretion rate onto the neutron star, which can be compared with the observed X-ray luminosity. We also report a revised valu…
Periodisko orbītu eksistence diskrētās dinamiskās sistēmās
2018
Bakalaura darbā apskatīti diskrētu dinamisku sistēmu pamatjēdzieni, akcentējot periodisko punktu eksistenci un to meklēšanu. Ar piemēriem parādīts, kā noskaidrot autonoma pirmās kārtas diferenču vienādojuma periodiskos punktus ar periodu 2 un 3. Darba lielākā daļa veltīta neautonomu pirmās kārtas diferenču vienādojumu periodisko punktu jeb ģeometrisko r-ciklu eksistencei, kur vienādojuma periodiskos koeficientus veido polinomi vai racionālas funkcijas.
Gabaliem lineāru diferenču vienādojumu sistēmu izpēte
2021
Maģistra darbā tiek apskatı̄ta gabaliem lineāru divu diferenču vienādojumu sistēmu lı̄dzsvara punktu stabilitāte. Ir atrasti vairāki kādas konkrētas diferenču vienādojumu sistēmas periodiskie atrisinājumi ar periodiem 5, 6, 7, 12 un pierādı̄ts, ka šai sistēmai neeksistē atrisinājums ar periodu 2.
Evidence of a non-conservative mass transfer in the ultra-compact X-ray source XB 1916-053
2020
The dipping source XB 1916-053 is a compact binary system with an orbital period of 50 min harboring a neutron star. Using ten new {\it Chandra} observations and one {\it Swift/XRT} observation, we are able to extend the baseline of the orbital ephemeris; this allows us to exclude some models that explain the dip arrival times. The Chandra observations provide a good plasma diagnostic of the ionized absorber and allow us to determine whether it is placed at the outer rim of the accretion disk or closer to the compact object. From the available observations we are able to obtain three new dip arrival times extending the baseline of the orbital ephemeris from 37 to 40 years. From the analysis…