1,283 research outputs found
General relativistic models for rotating magnetized neutron stars in conformally flat spacetime
The extraordinary energetic activity of magnetars is usually explained in
terms of dissipation of a huge internal magnetic field of the order of
G. How such a strong magnetic field can originate during the
formation of a neutron star is still subject of active research. An important
role can be played by fast rotation: if magnetars are born as millisecond
rotators dynamo mechanisms may efficiently amplify the magnetic field inherited
from the progenitor star during the collapse. In this case, the combination of
rapid rotation and strong magnetic field determine the right physical condition
not only for the development of a powerful jet driven explosion, manifesting as
a gamma ray burst, but also for a copious gravitational waves emission. Strong
magnetic fields are indeed able to induce substantial quadrupolar deformations
in the star. In this paper we analyze the joint effect of rotation and
magnetization on the structure of a polytropic and axisymmetric neutron star,
within the ideal magneto-hydrodynamic regime. We will consider either purely
toroidal or purely poloidal magnetic field geometries. Through the sampling of
a large parameter space, we generalize previous results in literature,
inferring new quantitative relations that allow for a parametrization of the
induced deformation, that takes into account also the effects due to the
stellar compactness and the current distribution. Finally, in the case of
purely poloidal field, we also discuss how different prescriptions on the
surface charge distribution (a gauge freedom) modify the properties of the
surrounding electrosphere and its physical implications.Comment: 25 pages, 17 figures, 6 tables, accepted for publication in MNRA
The role of currents distribution in general relativistic equilibria of magnetized neutron stars
Magnetic fields play a critical role in the phenomenology of neutron stars.
There is virtually no observable aspect which is not governed by them. Despite
this, only recently efforts have been done to model magnetic fields in the
correct general relativistic regime, characteristic of these compact objects.
In this work we present, for the first time a comprehensive and detailed
parameter study, in general relativity, of the role that the current
distribution, and the related magnetic field structure, have in determining the
precise structure of neutron stars. In particular, we show how the presence of
localized currents can modify the field strength at the stellar surface, and we
look for general trends, both in terms of energetic properties, and magnetic
field configurations. Here we verify that, among other things, for a large
class of different current distributions the resulting magnetic configurations
are always dominated by the poloidal component of the current.Comment: 14 pages, 13 figures, accepted for publication in MNRA
Modeling the structure of magnetic fields in Neutron Stars: from the interior to the magnetosphere
The phenomenology of the emission of pulsars and magnetars depends
dramatically on the structure and properties of their magnetic field. In
particular it is believed that the outbursting and flaring activity observed in
AXPs and SRGs is strongly related to their internal magnetic field. Recent
observations have moreover shown that charges are present in their
magnetospheres supporting the idea that their magnetic field is tightly twisted
in the vicinity of the star. In principle these objects offer a unique
opportunity to investigate physics in a regime beyond what can be obtained in
the laboratory. We will discuss the properties of equilibrium models of
magnetized neutron stars, and we will show how internal and external currents
can be related. These magnetic field configurations will be discussed
considering also their stability, relevant for their origin and possibly
connected to events like SNe and GRBs. We will also show what kind of
deformations they induce in the star, that could lead to emission of
gravitational waves. In the case of a twisted magnetosphere we will show how
the amount of twist regulates their general topology. A general formalism based
on the simultaneous numerical solution of the general relativistic
Grad-Shafranov equation and Einstein equations will be presented.Comment: 9 pages, 3 figures, Proceedings of the 10th International Conference
on Numerical Modeling of Space Plasma Flows, 8-12 June 2015, Avignon, Franc
Relativistic MHD modeling of magnetized neutron stars, pulsar winds, and their nebulae
Neutron stars are among the most fascinating astrophysical sources, being
characterized by strong gravity, densities about the nuclear one or even above,
and huge magnetic fields. Their observational signatures can be extremely
diverse across the electromagnetic spectrum, ranging from the periodic and
low-frequency signals of radio pulsars, up to the abrupt high-energy gamma-ray
flares of magnetars, where energies of ~10^46 erg are released in a few
seconds. Fast-rotating and highly magnetized neutron stars are expected to
launch powerful relativistic winds, whose interaction with the supernova
remnants gives rise to the non-thermal emission of pulsar wind nebulae, which
are known cosmic accelerators of electrons and positrons up to PeV energies. In
the extreme cases of proto-magnetars (magnetic fields of ~10^15 G and
millisecond periods), a similar mechanism is likely to provide a viable engine
for the still mysterious gamma-ray bursts. The key ingredient in all these
spectacular manifestations of neutron stars is the presence of strong magnetic
fields in their constituent plasma. Here we will present recent updates of a
couple of state-of-the-art numerical investigations by the high-energy
astrophysics group in Arcetri: a comprehensive modeling of the steady-state
axisymmetric structure of rotating magnetized neutron stars in general
relativity, and dynamical 3-D MHD simulations of relativistic pulsar winds and
their associated nebulae.Comment: EPS 44th Conference on Plasma Physics (June 2017, Belfast), paper
accepted for publication on Plasma Physics and Controlled Fusio
A webgis for the knowledge and conservation of the historical buildings in Sardinia (Italy)
The presented work is part of the research project, titled "Tecniche murarie tradizionali: conoscenza per la conservazione ed il miglioramento prestazionale" (Traditional building techniques: from knowledge to conservation and performance improvement). This research project has the purpose of studying the building techniques of the 13th- 18thcenturies in the Sardinia Region (Italy) for their knowledge, conservation, and promotion. The end purpose of the entire study is to improve the performance of the examined structures. In particular, the task of the authors within the research project was to build a WebGIS to manage the data collected during the examination and study phases. This infrastructure was entirely built using Open Source software. The work consisted of designing a database built in PostgreSQL and its spatial extension PostGIS, which allows storing and managing feature geometries and spatial data. The data input is performed via a form built in HTML and PHP. The HTML part is based on Bootstrap, an open tools library for websites and web applications. The implementation of this template used both PHP and Javascript code. The PHP code manages the reading and writing of data to the database, using embedded SQL queries. The database is published on the Internet as a WebGIS built using the Leaflet Javascript open libraries, which allows creating map sites with background maps and navigation, input and query tools. This too uses an interaction of HTML, Javascript, PHP and SQL code. The Database can be accessed in QGIS via a PostgreSQL connection. As of today, we surveyed and archived more than 300 buildings, belonging to three main macro categories: fortification architectures, religious architectures, residential architectures
General relativistic neutron stars with twisted magnetosphere
Soft Gamma-Ray Repeaters and Anomalous X-Ray Pulsars are extreme
manifestations of the most magnetized neutron stars: magnetars. The
phenomenology of their emission and spectral properties strongly support the
idea that the magnetospheres of these astrophysical objects are tightly twisted
in the vicinity of the star. Previous studies on equilibrium configurations
have so far focused on either the internal or the external magnetic field
configuration, without considering a real coupling between the two fields. Here
we investigate numerical equilibrium models of magnetized neutron stars endowed
with a confined twisted magnetosphere, solving the general relativistic
Grad-Shafranov equation both in the interior and in the exterior of the compact
object. A comprehensive study of the parameters space is provided to
investigate the effects of different current distributions on the overall
magnetic field structure.Comment: 15 pages, 14 figures. Accepted for publication in MNRA
A WEBGIS for the knowledge and conservation of the historical wall structures of the 13th–18th centuries
The presented work is part of the research project, titled "Tecniche murarie tradizionali: conoscenza per la conservazione ed il miglioramento prestazionale" (Traditional building techniques: from knowledge to conservation and performance improvement), with the purpose of studying the building techniques of the 13th–18th centuries in the Sardinia Region (Italy) for their knowledge, conservation, and promotion. The end purpose of the entire study is to improve the performance of the examined structures. In particular, the task of the authors within the research project was to build a WebGIS to manage the data collected during the examination and study phases. This infrastructure was entirely built using Open Source software. The work consisted of designing a database built in PostgreSQL and its spatial extension PostGIS, which allows to store and manage feature geometries and spatial data. The data input is performed via a form built in HTML and PHP. The HTML part is based on Bootstrap, an open tools library for websites and web applications. The implementation of this template used both PHP and Javascript code. The PHP code manages the reading and writing of data to the database, using embedded SQL queries. As of today, we surveyed and archived more than 300 buildings, belonging to three main macro categories: fortification architectures, religious architectures, residential architectures. The masonry samples investigated in relation to the construction techniques are more than 150. The database is published on the Internet as a WebGIS built using the Leaflet Javascript open libraries, which allows creating map sites with background maps and navigation, input and query tools. This too uses an interaction of HTML, Javascript, PHP and SQL code
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