535 research outputs found
Galclaim: A tool to identify host galaxy of astrophysical transient sources
The Galclaim software is designed to identify association between
astrophysical transient sources and host galaxy by computing the probability of
chance alignment. It is distributed as an open source Python software. It is
already used to identify, confirm or reject host galaxy candidates of GRBs and
to validate or invalidate transient candidates in astrophysical observations.
Such tools are also very useful to characterise archived transient candidates
in large sky survey telescopes
Elementary excitations in homogeneous superfluid neutron star matter: Role of the proton component
The thermal evolution of neuron stars depends on the elementary excitations
affecting the stellar matter. In particular, the low-energy excitations, whose
energy is proportional to the transfered momentum, can play a major role in the
emission and propagation of neutrinos. In this paper, we focus on the density
modes associated with the proton component in the homogeneous matter of the
outer core of neutron stars (at density between one and three times the nuclear
saturation density, where the baryonic constituants are expected to be neutrons
and protons). In this region, it is predicted that the protons are
superconductor. We study the respective roles of the proton pairing and Coulomb
interaction in determining the properties of the modes associated with the
proton component. This study is performed in the framework of the Random Phase
Approximation, generalized in order to describe the response of a superfluid
system.The formalism we use ensures that the Generalized Ward's Identities are
satisfied. An important conclusion of this work is the presence of a
pseudo-Goldstone mode associated with the proton superconductor in neutron-star
matter. Indeed, the Goldstone mode, which characterizes a pure superfluid, is
suppressed in usual superconductors due to the long-range Coulomb interaction,
which only allows a plasmon mode. However, for the proton component of stellar
matter, the Coulomb field is screened by the electrons and a pseudo-Goldstone
mode occurs, with a velocity increased by the Coulomb interaction.Comment: Submitted for publicatio
Elementary excitations in homogeneous neutron star matter
We study the collective density modes which can affect neutron-star
thermodynamics in the baryonic density range between nuclear saturation
() and . In this region, the expected constituents of
neutron-star matter are mainly neutrons, protons and electrons ( matter),
under the constraint of beta equilibrium. The elementary excitations of this
medium are studied in the RPA framework. We emphasize the effect of
Coulomb interaction, in particular the electron screening of the proton plasmon
mode. For the treatment of the nuclear interaction, we compare two modern
Skyrme forces and a microscopic approach. The importance of the nucleon
effective mass is observed.Comment: misprint corrected in Eq. (1
Phase transitions of hadronic to quark matter at finite T and \mu_B
The phase transition of hadronic to quark matter and the boundaries of the
mixed hadron-quark coexistence phase are studied within the two Equation of
State (EoS) model. The relativistic effective mean field approach with constant
and density dependent meson-nucleon couplings is used to describe hadronic
matter, and the MIT Bag model is adopted to describe quark matter. The
boundaries of the mixed phase for different Bag constants are obtained solving
the Gibbs equations.
We notice that the dependence on the Bag parameter of the critical
temperatures (at zero chemical potential) can be well reproduced by a fermion
ultrarelativistic quark gas model, without contribution from the hadron part.
At variance the critical chemical potentials (at zero temperature) are very
sensitive to the EoS of the hadron sector. Hence the study of the hadronic EoS
is much more relevant for the determination of the transition to the
quark-gluon-plasma at finite baryon density and low-T. Moreover in the low
temperature and finite chemical potential region no solutions of the Gibbs
conditions are existing for small Bag constant values, B < (135 MeV)^4. Isospin
effects in asymmetric matter appear relevant in the high chemical potential
regions at lower temperatures, of interest for the inner core properties of
neutron stars and for heavy ion collisions at intermediate energies.Comment: 24 pages and 16 figures (revtex4
Anomalous thermodynamics and phase transitions of neutron-star matter
In this letter we show that the presence of the long-range Coulomb force in
dense stellar matter implies that the total charge cannot be associated with a
chemical potential, even if it is a conserved quantity. As a further
consequence, the analytical properties of the partition sum are modified,
changing the order of the phase transitions and affecting the possible
occurrence of critical behaviours. The peculiar thermodynamic properties of the
system can be understood introducing a model hamiltonian in which each charge
is independently neutralized by a uniform background of opposite charge.Comment: 4 pages - GANIL, LP
Plasmon excitations in homogeneous neutron star matter
We study the possible collective plasma modes which can affect neutron-star
thermodynamics and different elementary processes in the baryonic density range
between nuclear saturation () and . In this region, the
expected constituents of neutron-star matter are mainly neutrons, protons,
electrons and muons ( matter), under the constraint of beta
equilibrium. The elementary plasma excitations of the three-fluid
medium are studied in the RPA framework. We emphasize the relevance of the
Coulomb interaction among the three species, in particular the interplay of the
electron and muon screening in suppressing the possible proton plasma mode,
which is converted into a sound-like mode. The Coulomb interaction alone is
able to produce a variety of excitation branches and the full spectral function
shows a rich structure at different energy. The genuine plasmon mode is pushed
at high energy and it contains mainly an electron component with a substantial
muon component, which increases with density. The plasmon is undamped for not
too large momentum and is expected to be hardly affected by the nuclear
interaction. All the other branches, which fall below the plasmon, are damped
or over-damped.Comment: misprint corrected in Eq. (1
Spectroscopy of Na: Bridging the two-proton radioactivity of Mg
The unbound nucleus Na, the intermediate nucleus in the two-proton
radioactivity of Mg, was studied by the measurement of the resonant
elastic scattering reaction Ne(p,Ne)p performed at 4 A.MeV.
Spectroscopic properties of the low-lying states were obtained in a R-matrix
analysis of the excitation function. Using these new results, we show that the
lifetime of the Mg radioactivity can be understood assuming a sequential
emission of two protons via low energy tails of Na resonances
Upper limits on the observational effects of nuclear pasta in neutron stars
The effects of the existence of exotic nuclear shapes at the bottom of the
neutron star inner crust - nuclear `pasta' - on observational phenomena are
estimated by comparing the limiting cases that those phases have a vanishing
shear modulus and that they have the shear modulus of a crystalline solid . We
estimate the effect on torsional crustal vibrations and on the maximum
quadrupole ellipticity sustainable by the crust. The crust composition and
transition densities are calculated consistently with the global properties,
using a liquid drop model with a bulk nuclear equation of state (EoS) which
allows a systematic variation of the nuclear symmetry energy. The symmetry
energy J and its density dependence L at nuclear saturation density are the
dominant nuclear inputs which determine the thickness of the crust, the range
of densities at which pasta might appear, as well as global properties such as
the radius and moment of inertia. We show the importance of calculating the
global neutron star properties on the same footing as the crust EoS, and
demonstrate that in the range of experimentally acceptable values of L, the
pasta phase can alter the crust frequencies by up to a factor of three,
exceeding the effects of superfluidity on the crust modes, and decrease the
maximum quadrupole ellipticity sustainable by the crust by up to an order of
magnitude. The signature of the pasta phases and the density dependence of the
symmetry energy on the potential observables highlights the possibility of
constraining the EoS of dense, neutron-rich matter and the properties of the
pasta phases using astrophysical observations.Comment: 8 pages, 7 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Properties of the nuclear medium
We review our knowledge on the properties of the nuclear medium that have
been studied, along many years, on the basis of many-body theory, laboratory
experiments and astrophysical observations. First we consider the realm of
phenomenological laboratory data and astrophysical observations, and the hints
they can give on the characteristics that the nuclear medium should possess.
The analysis is based on phenomenological models, that however have a strong
basis on physical intuition and an impressive success. More microscopic models
are also considered, and it is shown that they are able to give invaluable
information on the nuclear medium, in particular on its Equation of State. The
interplay between laboratory experiments and astrophysical observations are
particularly stressed, and it is shown how their complementarity enriches
enormously our insights into the structure of the nuclear medium. We then
introduce the nucleon-nucleon interaction and the microscopic many-body theory
of nuclear matter, with a critical discussion about the different approaches
and their results. The Landau Fermi Liquid theory is introduced and briefly
discussed. As illustrative example, we discuss neutron matter at very low
density, and it is shown how it can be treated within the many-body theory. A
section is dedicated to the pairing problem. The connection with nuclear
structure is then discussed, on the basis of the Energy Density Functional
method. The possibility to link the physics of exotic nuclei and the
astrophysics of neutron stars is particularly stressed. Finally we discuss the
thermal properties of the nuclear medium, in particular the liquid-gas phase
transition and its connection with the phenomenology on heavy ion reactions and
the cooling evolution of neutron stars. The presentation has been taken for
non-specialists and possibly for non-nuclear physicists.Comment: 90 pages, 29 figures, revised versio
The GRANDMA network in preparation for the fourth gravitational-wave observing run
GRANDMA is a world-wide collaboration with the primary scientific goal ofstudying gravitational-wave sources, discovering their electromagneticcounterparts and characterizing their emission. GRANDMA involves astronomers,astrophysicists, gravitational-wave physicists, and theorists. GRANDMA is now atruly global network of telescopes, with (so far) 30 telescopes in bothhemispheres. It incorporates a citizen science programme (Kilonova-Catcher)which constitutes an opportunity to spread the interest in time-domainastronomy. The telescope network is an heterogeneous set of already-existingobserving facilities that operate coordinated as a single observatory. Withinthe network there are wide-field imagers that can observe large areas of thesky to search for optical counterparts, narrow-field instruments that dotargeted searches within a predefined list of host-galaxy candidates, andlarger telescopes that are devoted to characterization and follow-up of theidentified counterparts. Here we present an overview of GRANDMA after the thirdobserving run of the LIGO/VIRGO gravitational-wave observatories in and its ongoing preparation for the forthcoming fourth observational campaign(O4). Additionally, we review the potential of GRANDMA for the discovery andfollow-up of other types of astronomical transients.<br
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