4,404 research outputs found
Spatial identification of the overionized plasma in W49B
Recent Suzaku X-ray observations of the ejecta-dominated supernova remnant
W49B have shown that in the global spectrum there is a clear indication for the
presence of overionized plasma whose physical origin is still under debate. In
order to ascertain the physical origin of such a rapidly cooling plasma, we
focus on the study of its spatial localization within the X-ray emitting
ejecta. We confirm the presence of a saw-edged excess (interpreted as a strong
radiative recombination continuum) in the global spectrum above 8 keV, emerging
above the ionization-equilibrium model. We produce a hardness ratio map to
determine where the plasma is overionized and we perform a spectral analysis of
the regions with and without strong overionization. We find that the
overionized plasma is localized in the center of the remnant and in its western
jet, while it is not detected in the bright eastern jet, where the expansion of
the ejecta is hampered by their interaction with a dense interstellar cloud.
The location of overionized plasma suggests that the inner ejecta are rapidly
cooling by expansion, unlike the outer ejecta, for which expansion is hampered
by interstellar clouds seen in H2Comment: Accepted for publication as a Letter in Astronomy and Astrophysics
Origin of asymmetries in X-ray emission lines from the blast wave of the 2014 outburst of nova V745 Sco
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 the ejecta distribution are efficiently collimated in polar directions
due to the presence of the equatorial density enhancement. The majority of the
X-ray emission originates from the interaction of the blast with the equatorial
density enhancement and is concentrated on the equatorial plane as a ring-like
structure. Our "best-fit" model requires a mass of ejecta in the outburst
and an explosion energy erg and reproduces the distribution of emission
measure vs temperature and the evolution of shock velocity and temperature
inferred from the observations. The model predicts asymmetric and blue-shifted
line profiles similar to those observed and explains their origin as due to
substantial X-ray absorption of red-shifted emission by ejecta material. The
comparison of predicted and observed Ne and O spectral line ratios reveals no
signs of strong Ne enhancement and suggests the progenitor is a CO white dwarf.Comment: 16 pages, 17 Figures; accepted for publication on MNRA
Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta
The remnants of core-collapse supernovae (SNe) have complex morphologies that
may reflect asymmetries and structures developed during the progenitor SN
explosion. Here we investigate how the morphology of the SNR Cassiopeia A (Cas
A) reflects the characteristics of the progenitor SN with the aim to derive the
energies and masses of the post-explosion anisotropies responsible for the
observed spatial distribution of Fe and Si/S. We model the evolution of Cas A
from the immediate aftermath of the progenitor SN to the three-dimensional
interaction of the remnant with the surrounding medium. The post-explosion
structure of the ejecta is described by small-scale clumping of material and
larger-scale anisotropies. The hydrodynamic multi-species simulations consider
an appropriate post-explosion isotopic composition of the ejecta. The observed
average expansion rate and shock velocities can be well reproduced by models
with ejecta mass and explosion energy erg. The post-explosion anisotropies (pistons)
reproduce the observed distributions of Fe and Si/S if they had a total mass of
and a total kinetic energy of erg. The pistons produce a spatial inversion of ejecta layers at the
epoch of Cas A, leading to the Si/S-rich ejecta physically interior to the
Fe-rich ejecta. The pistons are also responsible for the development of bright
rings of Si/S-rich material which form at the intersection between the reverse
shock and the material accumulated around the pistons during their propagation.
Our result supports the idea that the bulk of asymmetries observed in Cas A are
intrinsic to the explosion.Comment: 19 pages, 14 Figures; accepted for publication on Ap
Spatial distribution of X-ray emitting ejecta in Tycho's SNR: indications of shocked Titanium
Young supernova remnants show a characteristic ejecta-dominated X-ray
emission that allows us to probe the products of the explosive nucleosynthesis
processes and to ascertain important information about the physics of the
supernova explosions. Hard X-ray observations have recently revealed the
radioactive decay lines of 44Ti at ~67.9 keV and ~78.4 keV in the Tycho's SNR.
We here analyze the set of XMM-Newton archive observations of the Tycho's SNR.
We produce equivalent width maps of the Fe K and Ca XIX emission lines and find
indications for a stratification of the abundances of these elements and
significant anisotropies. We then perform a spatially resolved spectral
analysis by identifying five different regions characterized by high/low values
of the Fe K equivalent width. We find that the spatial distribution of the Fe K
emission is correlated with that of the Cr XXII. We also detect the Ti K-line
complex in the spectra extracted from the two regions with the highest values
of the Fe and Cr equivalent widths. The Ti line emissions remains undetected in
regions where the Fe and Cr equivalent widths are low. Our results indicate
that the post-shock Ti is spatially co-located with other iron-peak nuclei in
Tycho's SNR, in agreement with the predictions of multi-D models of Type Ia
supernovae.Comment: Accepted for publication in Ap
Linking gamma-ray spectra of supernova remnants to the cosmic ray injection properties in the aftermath of supernovae
The acceleration times of the highest-energy particles which emit gamma-rays
in young and middle-age SNRs are comparable with SNR age. If the number of
particles starting acceleration was varying during early times after the
supernova explosion then this variation should be reflected in the shape of the
gamma-ray spectrum. We use the solution of the non-stationary equation for
particle acceleration in order to analyze this effect. As a test case, we apply
our method to describe gamma-rays from IC443. As a proxy of the IC443 parent
supernova we consider SN1987A. First, we infer the time dependence of injection
efficiency from evolution of the radio spectral index in SN1987A. Then, we use
the inferred injection behavior to fit the gamma-ray spectrum of IC443. We show
that the break in the proton spectrum needed to explain the gamma-ray emission
is a natural consequence of the early variation of the cosmic ray injection,
and that the very-high energy gamma-rays originate from particles which began
acceleration during the first months after the supernova explosion. We conclude
that the shape of the gamma-ray spectrum observed today in SNRs critically
depends on the time variation of the cosmic ray injection process in the
immediate post explosion phases. With the same model, we estimate also the
possibility in the future to detect gamma-rays from SN 1987A.Comment: A&A, accepte
SNRs as cosmic accelerators
Supernova remnants are considered to be the main source of galactic cosmic rays up to the knee of the cosmic rays energy distribution. I review the increasing set of indications supporting this scenario together with the main open issues
The Italian version of the Thinking About Life Experiences Questionnaire and its relationship with gender, age, and life events on Facebook
The present study provided a cross-cultural validation of the Thinking About Life Experiences Scale-revised (TALE-R) in an Italian sample of Facebook users (n = 492; female = 378; male = 114; mean age 26.1) to test for replication and universality of the TALE-R three-factor model. Furthermore, it explored the interrelations among gender, age, the scores at the TALE-R and the frequency of posting textual/visual information about individuals' life events on Facebook. Results at exploratory and confirmatory factor analysis gave empirical support to both of a tripartite model for the functions of autobiographical memory (i.e., directive-behavior, social-bonding, and self-continuity) and measurement invariance of this three-factor model across gender and age. Further results at linear correlation and regression analyses showed that directive-behavior and self-continuity functions of autobiographical memory are significantly related to the ways people use Facebook for personal documentation. Age differences more than gender influence this association. Discussion and conclusion reported both theoretical and empirical implications of the findings of the study
L\u2019interdipendenza delle obbligazioni nella compravendita conclusa tramite intermediario libero (\u2018institor\u2019 o \u2018procurator\u2019)
Il lavoro si occupa dell'interdipendenza delle prestazioni nell'ambito del negozio di compravendita nelle fonti del diritto romano.In particolare, il problema viene studiato in relazzione alle compravendite concluse da un intermediario, institor o procurator
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