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On the Spectrum and Polarization of Magnetar Flare Emission

Authors :
Roberto Taverna
Roberto Turolla
Source :
Galaxies, Vol 6, Iss 1, p 35 (2018)
Publication Year :
2018
Publisher :
MDPI AG, 2018.

Abstract

Bursts and flares are among the distinctive observational manifestations of magnetars, isolated neutron stars endowed with an ultra-strong magnetic field ( B ≈ 10 14 – 10 15 G). It is believed that these events arise in a hot electron-positron plasma, injected in the magnetosphere, due to a magnetic field instability, which remains trapped within the closed magnetic field lines (the “trapped-fireball” model). We have developed a simple radiative transfer model to simulate magnetar flare emission in the case of a steady trapped fireball. After dividing the fireball surface in a number of plane-parallel slabs, the local spectral and polarization properties are obtained integrating the radiative transfer equations for the two normal modes. We assume that magnetic Thomson scattering is the dominant source of opacity, and neglect contributions from second-order radiative processes, although the presence of double-Compton scattering is accounted for in establishing local thermal equilibrium in the fireball atmospheric layers. The spectra we obtained in the 1–100 keV energy range are in broad agreement with those of available observations. The large degree of polarization (≳80%) predicted by our model should be easily detectable by new-generation X-ray polarimeters, like IXPE, XIPE and eXTP, allowing one to confirm the model predictions.

Details

Language :
English
ISSN :
20754434
Volume :
6
Issue :
1
Database :
Directory of Open Access Journals
Journal :
Galaxies
Publication Type :
Academic Journal
Accession number :
edsdoj.4a5b3e54f0cf42ab8a543b91216cc781
Document Type :
article
Full Text :
https://doi.org/10.3390/galaxies6010035