Search results for "Planetary Science"
showing 10 items of 4367 documents
On the influence of a hybrid thermal-non-thermal distribution in the internal shocks model for blazars
2017
Internal shocks occurring in blazars may accelerate both thermal and non-thermal electrons. In this paper we examine the consequences that such a hybrid (thermal/non-thermal) EED has on the spectrum of blazars. Since the thermal component of the EED may extend to very low energies. We replace the standard synchrotron process by the more general magneto-bremsstrahlung (MBS). Significant differences in the energy flux appear at low radio frequencies when considering MBS instead of the standard synchrotron emission. A drop in the spectrum appears in the all the radio band and a prominent valley between the infrared and soft X-rays bands when a hybrid EED is considered, instead of a power-law E…
Testing jet geometries and disc-jet coupling in the neutron star LMXB 4U 0614 + 091 with the internal shocks model
2020
Multi-wavelength spectral energy distributions of Low Mass X-ray Binaries in the hard state are determined by the emission from a jet, for frequencies up to mid-infrared, and emission from the accretion flow in the optical to X-ray range. In the last years, the flat radio-to-mid-IR spectra of Black Hole (BH) X-ray binaries was described using the internal shocks model, which assumes that the fluctuations in the velocity of the ejecta along the jet are driven by the fluctuations in the accretion flow, described by the X-ray Power Density Spectrum (PDS). In this work we attempt to apply this model for the first time to a Neutron Star (NS) LMXB, i.e. 4U 0614+091. We used the multi-wavelength d…
Origin of asymmetries in X-ray emission lines from the blast wave of the 2014 outburst of nova V745 Sco
2016
The symbiotic nova V745 Sco was observed in outburst on 2014 February 6. Its observations by the Chandra X-ray Observatory at days 16 and 17 have revealed a spectrum characterized by asymmetric and blue-shifted emission lines. Here we investigate the origin of these asymmetries through three-dimensional hydrodynamic simulations describing the outburst during the first 20 days of evolution. The model takes into account thermal conduction and radiative cooling and assumes a blast wave propagates through an equatorial density enhancement. From the simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra. We find that both the blast wave and th…
The fully developed remnant of a neutrino-driven supernova: Evolution of ejecta structure and asymmetries in SNR Cassiopeia A
2020
Abridged. We aim at exploring to which extent the remnant keeps memory of the asymmetries that develop stochastically in the neutrino-heating layer due to hydrodynamic instabilities (e.g., convective overturn and the standing accretion shock instability) during the first second after core bounce. We coupled a 3D HD model of a neutrino-driven SN explosion with 3D MHD/HD simulations of the remnant formation. The simulations cover 2000 years of expansion and include all physical processes relevant to describe the complexities in the SN evolution and the subsequent interaction of the stellar debris with the wind of the progenitor star. The interaction of large-scale asymmetries left from the ea…
Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments
2021
Aims. EXor-type objects are protostars that display powerful UV-optical outbursts caused by intermittent and powerful events of magnetospheric accretion. These objects are not yet well investigated and are quite difficult to characterize. Several parameters, such as plasma stream velocities, characteristic densities, and temperatures, can be retrieved from present observations. As of yet, however, there is no information about the magnetic field values and the exact underlying accretion scenario is also under discussion. Methods. We use laboratory plasmas, created by a high power laser impacting a solid target or by a plasma gun injector, and make these plasmas propagate perpendicularly to …
Modeling the remnants of core-collapse supernovae from luminous blue variable stars
2021
LBVs are massive evolved stars that suffer sporadic and violent mass-loss events. They have been proposed as the progenitors of some core-collapse SNe, but this idea is still debated due to the lack of direct evidence. Since SNRs can carry in their morphology the fingerprints of the progenitor stars as well as of the inhomogeneous CSM sculpted by the progenitors, the study of SNRs from LBVs could help to place core-collapse SNe in context with the evolution of massive stars. We investigate the physical, chemical and morphological properties of the remnants of SNe originating from LBVs, in order to search for signatures, revealing the nature of the progenitors, in the ejecta distribution and…
Indications of a Si-rich bilateral jet of ejecta in the Vela SNR observed with XMM-Newton
2017
Context. The Vela supernova remnant displays several ejecta, which are fragment-like features protruding beyond the front of its primary blast shock wave. They appear to be "shrapnel", bowshock-shaped relics of the supernova explosion. One of these pieces of shrapnel (A), located in the northeastern edge of the remnant, is peculiar because its X-ray spectrum exhibits a high Si abundance, in contrast to the other observed ejecta fragments, which show enhanced O, Ne, and Mg abundances. Aims. In this Letter we present the analysis of another ejecta fragment located opposite to shrapnel A with respect to the center of the shell, in the southwestern boundary of the remnant, named shrapnel G. We …
Cosmological shock waves: clues to the formation history of haloes
2012
Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal w…
3D MHD modeling of the expanding remnant of SN 1987A : role of magnetic field and non-thermal radio emission
2018
Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field on the dynamics of the expanding remnant of SN 1987A and the origin and evolution of the radio emission from the remnant, in particular, during the interaction of the blast wave with the nebula surrounding the SN. Methods. We model the evolution of SN 1987A from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula by 3D MHD simulations. The model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-SN ambie…
Axisymmetric simulations of magnetorotational core collapse: approximate inclusion of general relativistic effects
2006
We continue our investigations of the magnetorotational collapse of stellar cores discussing simulations performed with a modified Newtonian gravitational potential that mimics general relativistic effects. The approximate TOV potential used in our simulations catches several features of fully relativistic simulations quite well. It is able to correctly reproduce the behavior of models which show a qualitative change both of the dynamics and the gravitational wave signal when switching from Newtonian to fully relativistic simulations. If this is not the case, the Newtonian and the approximate TOV models differ quantitatively. The collapse proceeds to higher densities with the approximate TO…