Search results for "STELLA"
showing 10 items of 1995 documents
The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy
2021
We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGN) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband ($0.3\mbox{--}79$ keV) spectrum shows the presence of a power-law continuum with a soft excess below $2$ keV, iron K$\alpha$ emission ($\sim 6.4$ keV), and a Compton hump (peaking at $\sim 20$ keV). We find that the soft excess can be modeled by two different possible scenarios: a warm ($kT_\mathrm{e}\sim0.2$ keV) and optically thick ($\tau\sim34$) Comptonizing corona; or with relativistically-blurred reflection off a high-density ($\log{[n_\mathrm{e}/\mathrm{cm}^{-3}]}>18.3$) inner disk. These two models cannot be e…
Interpretation of AMS-02 electrons and positrons data
2014
We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positron…
Broadband spectral analysis of MXB 1659−298 in its soft and hard state
2018
The X-ray transient eclipsing source MXB 1659-298 went into outburst in 1999 and 2015. During these two outbursts the source was observed by XMM-Newton, nuSTAR, and Swift/XRT. Using these observations, we studied the broadband spectrum of the source to constrain the continuum components and to verify whether it had a reflection component, as is observed in other X-ray eclipsing transient sources. We combined the available spectra to study the soft and hard state of the source in the 0.45-55 keV energy range. We report a reflection component in the soft and hard state. The direct emission in the soft state can be modeled with a thermal component originating from the inner accretion disk plus…
High Energy Emission from Shocks Due to Jets and Accretion in Young Stars with Disks: Combining Observations, Numerical Models, and Laboratory Experi…
2018
High energy emission from young stars with disks, with all their components due to accretion and outflow activity, can have a deep impact on the evolution of their disks and on the formation of exo-planetary systems. An inter-disciplinary approach, which combines multi-wavelength observations, magnetohydrodynamical models, and laboratory experiments, allows us to get a more complete description of the accretion/ejection phenomena characterizing young stars. We discuss the case of the HH 154 jet, its X-ray emission localized at the base of the jet and its complex morphology, comparing observations, models, and laser experiments. We present the comparison between magnetohydrodynamical models …
On the runaway instability of self-gravitating torus around black holes
2010
Black holes surrounded by self-gravitating tori are astrophysical systems which may naturally form following the core collapse of a massive star or the merger of two neutron stars. We present here results from fully general relativistic numerical simulations of such systems in order to assess the influence of the torus self-gravity on the onset of the so-called runaway instability. This instability, which might drive the rapid accretion of the disk on shorter timescales than those required to power a relativistic fireball, potentially challenges current models of gamma-ray bursts. Our simulations indicate that the self-gravity of the torus does not actually favour the onset of the instabili…
Fallback accretion onto magnetized neutron stars and the hidden magnetic field model
2015
The observation of several neutron stars with relatively low values of the surface magnetic field found in supernova remnants has led in recent years to controversial interpretations. A possible explanation is the slow rotation of the proto-neutron star at birth which is unable to amplify its magnetic field to typical pulsar levels. An alternative possibility, the hidden magnetic field scenario, seems to be favoured over the previous one due to the observation of three low magnetic field magnetars. This scenario considers the accretion of the fallback of the supernova debris onto the neutron star as the responsible for the observed low magnetic field. In this work, we have studied under whi…
Stellar physics with the ALHAMBRA photometric system
2011
GREAT-ESF Workshop: Stellar Atmospheres in the Gaia Era 23–24 June 2011, Vrije Universiteit Brussels, Belgium.
Studying the microlenses mass function from statistical analysis of the caustic concentration
2011
The statistical distribution of caustic crossings by the images of a lensed quasar depends on the properties of the distribution of microlenses in the lens galaxy. We use a procedure based in Inverse Polygon Mapping to easily identify the critical and caustic curves generated by a distribution of stars in the lens galaxy. We analyze the statistical distributions of the number of caustic crossings by a pixel size source for several projected mass densities and different mass distributions. We compare the results of simulations with theoretical binomial distributions. Finally we apply this method to the study of the stellar mass distribution in the lens galaxy of QSO 2237+0305.
Dynamics of oscillating magnetized relativistic tori around a Schwarzschild black hole
2007
We present a comprehensive numerical study of the dynamics of magnetized relativistic axisymmetric tori orbiting in the background spacetime of a Schwarzschild black hole. The tori are modeled as having a purely toroidal magnetic field and a constant distribution of the specific angular momentum. Following previous investigations of tori in a purely hydrodynamical context, the dynamics of these objects has been studied upon the introduction of a perturbation which, for the values of the magnetic field considered here, triggers quasi-periodic oscillations (QPOs) lasting tens of orbital periods. As in the hydrodynamical case, the spectral distribution of the eigenfrequencies shows the presenc…
The relative role of EUV radiation and X-rays in the heating of hydrogen-rich exoplanet atmospheres
2009
Aims. We study the relative role of EUV and X-ray radiation in the heating of hydrogen-rich planet atmospheres with different composition and electron content. Methods. An accurate photo-ionization model has been used to follow the primary photo-electron energy deposition throughout the atmosphere. Results. Heating rates and efficiencies have been computed, together with column density cut-offs at which photons of given energies stop their heating production inside the atmosphere. Assuming 100 eV as the energy borderline between the extreme ultraviolet spectral range and X-rays we find that when the absorbing hydrogen column density is higher than 10 20 cm −2 only X-rays can heat the gas. E…