Search results for "ACCRETION DISCS"
showing 8 items of 38 documents
Dynamics in the Magnetospheres of Compact Objects
2020
Esta tesis doctoral explora el modelado de la dinámica en las magnetosferas alrededor de objetos compactos (agujeros negros y estrellas de neutrones), y sus implicaciones en la formación de fenómenos de alta energía como las llamaradas en magnetares y la emisión de alta variabilidad en el rango de los teraelectronvoltios (TeV) de algunos núcleos galácticos activos, por medio de simulaciones numéricas. Las sorprendentes imágenes de las sombras de los agujeros negros (BH) del centro galáctico y la galaxia M87 proporcionan una primera visión directa de la física de los flujos de acreción en los entornos más extremos del universo. La extracción eficiente de energía en forma de flujos de plasma …
Quasi-periodic dipping in the ultraluminous X-ray source, NGC 247 ULX-1
2021
Most ultraluminous X-ray sources (ULXs) are believed to be stellar mass black holes or neutron stars accreting beyond the Eddington limit. Determining the nature of the compact object and the accretion mode from broadband spectroscopy is currently a challenge, but the observed timing properties provide insight into the compact object and details of the geometry and accretion processes. Here we report a timing analysis for an 800 ks XMM-Newton campaign on the supersoft ultraluminous X-ray source, NGC 247 ULX-1. Deep and frequent dips occur in the X-ray light curve, with the amplitude increasing with increasing energy band. Power spectra and coherence analysis reveals the dipping preferential…
The BeppoSAX 0.1 - 18 keV Spectrum of the Bright Atoll Source GX 9+1: an Indication of the Source Distance
2005
We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12 - 18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color - color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of similar to 1.4 x 10(22) cm(-2), fits the spectra in the energy range 1 - 18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12 - 18 keV energy range, is well fitted by the model above, if we us…
Pre-main-sequence stars older than 8 Myr in the Eagle nebula
2013
The enigmatic young brown dwarf binary FU Tau: accretion and activity
2010
FU Tau belongs to a rare class of young, wide brown dwarf binaries. We have resolved the system in a Chandra X-ray observation and detected only the primary, FU Tau A. Hard X-ray emission, presumably from a corona, is present but, unexpectedly, we detect also a strong and unusually soft component from FU Tau A. Its X-ray properties, so far unique among brown dwarfs, are very similar to those of the T Tauri star TW Hya. The analogy with TW Hya suggests that the dominating soft X-ray component can be explained by emission from accretion shocks. However, the typical free-fall velocities of a brown dwarf are too low for an interpretation of the observed X-ray temperature as post-shock region. O…
Mass accretion to young stars triggered by flaring activity in circumstellar discs
2011
Young low-mass stars are characterized by ejection of collimated outflows and by circumstellar discs which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn remove the excess angular momentum from the star-disc system. However, although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. A point not considered to date and relevant for the accretion process is the evidence of very energetic and frequent flaring events in these stars. Flares may easily perturb the stability of the discs, thus influencing th…
Numerical relativity simulations of tilted black hole-torus systems
2016
Las fusiones de objetos compactos se encuentran entre los eventos más interesantes de la astrofísica relativista, siendo, en particular, el principal objetivo de la astronomía de ondas gravitatorias. En esta tesis investigamos los posibles estados finales de la fusión de sistemas binarios formados por agujero negro-estrella de neutrones o por dos estrellas de neutrones: discos gruesos (o toros) de acrecimiento alrededor de agujeros negros en rotación tipo Kerr. Estos sistemas agujero negro-toro se cree que constituyen el motor central de los eventos más luminosos del Universo: los llamados estallidos de rayos gamma. Nuestro conocimiento sobre la evolución y la estabilidad de estos sistemas …
Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field
2014
International audience; Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recentl…