2,951 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
Multiple scattering measurements in laboratory and foggy atmosphere
Multiple scattering affects propagation of light beams in turbid media. Backscattering or forward scattering based measurements of atmospheric parameters are influenced by this effect. Although largely studied theoretically, the effect needs measurements in control of situations due to the large variety of situations of practical importance. The results of laboratory measurements pertaining to the transmission of a collimated light beam (Helium-Neon souce, 10 mW) through suspensions of latex spheres in water are presented and a comparison was made with the predictions of calculation in a foggy atmosphere will also be presented
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
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