اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe magnetar emission in the IR band: the role of magnetospheric currents
68
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
There is a general consensus about the fact that the magnetar scenario provides a convincing explanation for several of the observed properties of the Anomalous X-ray Pulsars and the Soft Gamma Repeaters. However, the origin of the emission observed at low energies is still an open issue. We present a quantitative model for the emission in the optical/infrared band produced by curvature radiation from magnetospheric charges, and compare results with current magnetars observations.
قيم البحث
اقرأ أيضاً
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 rela
tivistic 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.
We perform a detailed modelling of the post-outburst surface emission of the low magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this source, B=6x10^12 G estimated from its spin-down rate, is in the observed range of magnetic fie
lds for normal pulsars. The source is further characterized by a high pulse fraction and a single-peak profile. Using synthetic temperature distribution profiles, and fully accounting for the general-relativistic effects of light deflection and gravitational redshift, we generate synthetic X-ray spectra and pulse profiles that we fit to the observations. We find that asymmetric and symmetric surface temperature distributions can reproduce equally well the observed pulse profiles and spectra of SGR 0418. Nonetheless, the modelling allows us to place constraints on the system geometry (i.e. the angles $psi$ and $xi$ that the rotation axis makes with the line of sight and the dipolar axis, respectively), as well as on the spot size and temperature contrast on the neutron star surface. After performing an analysis iterating between the pulse profile and spectra, as done in similar previous works, we further employed, for the first time in this context, a Markov-Chain Monte-Carlo approach to extract constraints on the model parameters from the pulse profiles and spectra, simultaneously. We find that, to reproduce the observed spectrum and flux modulation: (a) the angles must be restricted to $65deg < psi+xi < 125deg$ or $235deg < psi+xi <295deg$; (b) the temperature contrast between the poles and the equator must be at least a factor of $sim6$, and (c) the size of the hottest region ranges between 0.2-0.7 km (including uncertainties on the source distance). Last, we interpret our findings within the context of internal and external heating models.
The magnetar 4U~0142+61 has been well studied at optical and infrared wavelengths and is known to have a complicated broad-band spectrum over the wavelength range. Here we report the result from our linear imaging polarimetry of the magnetar at optic
al $I$-band. From the polarimetric observation carried out with the 8.2-m Subaru telescope, we determine the degree of linear polarization $P=1.0pm$3.4%, or $Pleq$5.6% (90% confidence level). Considering models suggested for optical emission from magnetars, we discuss the implications of our result. The upper limit measurement indicates that different from radio pulsars, magnetars probably would not have strongly polarized optical emission if the emission arises from their magnetosphere as suggested.
A new and more comprehensive model of charge-exchange induced X-ray emission, due to ions precipitating into the Jovian atmosphere near the poles, has been used to analyze spectral observations made by the Chandra X-ray Observatory. The model include
s for the first time carbon ions, in addition to the oxygen and sulfur ions previously considered, in order to account for possible ion origins from both the solar wind and the Jovian magnetosphere. By comparing the model spectra with newly reprocessed Chandra observations, we conclude that carbon ion emission provides a negligible contribution, suggesting that solar wind ions are not responsible for the observed polar X-rays. In addition, results of the model fits to observations support the previously estimated seeding kinetic energies of the precipitating ions (~0.7-2 MeV/u), but infer a different relative sulfur to oxygen abundance ratio for these Chandra observations.
A520 is a hot and luminous galaxy cluster, where gravitational lensing and X-ray measures reveal a different spatial distribution of baryonic and Dark Matter. This cluster hosts a radio halo, whose map shows a separation between the North-East and th
e South-West part of the cluster, similarly to what is observed in gravitational lensing maps. In this paper we study the possibility that the diffuse radio emission in this cluster is produced by Dark Matter annihilation. We find that in the whole cluster the radio emission should be dominated by baryonic phenomena; if a contribution from Dark Matter is present, it should be searched in a region in the NE part of the cluster, where a peak of the radio emission is located close to a Dark Matter sub-halo, in a region where the X-ray emission is not very strong. By estimating the radio spectrum integrated in this region using data from publicly available surveys, we find that this spectrum can be reproduced by a Dark Matter model for a neutralino with mass 43 GeV and annihilation final state $b bar b$ for a magnetic field of 5 $mu$G.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
