X-ray perspective of the twisted magnetospheres of magnetars

Journal Article · Wed May 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/805/1/81· OSTI ID:22883172

Weng, Shan-Shan; Göğüş, Ersin ^[1]; Güver, Tolga ^[2]; Lin, Lin ^[3]

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1. Sabancı University, Faculty of Engineering and Natural Sciences, Orhanlı Tuzla 34956 Istanbul (Turkey)
2. Istanbul University, Science Faculty, Department of Astronomy and Space Sciences, Beyazıt, 34119, Istanbul (Turkey)
3. François Arago Centre, APC, Université Paris Diderot, CNRS/IN2P3 13 rue Watt, F-75013 Paris (France)

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are recognized as the most promising magnetar candidates, as indicated by their energetic bursts and rapid spin-downs. It is expected that the strong magnetic field leaves distinctive imprints on the emergent radiation both by affecting the radiative processes in atmospheres of magnetars and by scattering in the upper magnetospheres. We construct a self-consistent physical model that incorporates emission from the magnetar surface and its reprocessing in the three-dimensional (3D) twisted magnetosphere using a Monte Carlo technique. The synthetic spectra are characterized by four parameters: surface temperature kT, surface magnetic field strength B, magnetospheric twist angle Δϕ, and the normalized electron velocity β. We also create a tabular model (STEMS3D) and apply it to a large sample of XMM-Newton spectra of magnetars. The model successfully fits nearly all spectra, and the obtained magnetic field for 7 out of the 11 sources are consistent with the values inferred from the spin-down rates. We conclude that the continuum-fitting by our model is a robust method to measure the magnetic field strength and magnetospheric configuration of AXPs and SGRs. Investigating the multiple observations of variable sources, we also study the mechanism of their spectral evolution. Our results suggest that the magnetospheres in these sources are highly twisted (Δϕ>1), and the behavior of magnetospheric twisting and untwisting is revealed in the 2002 outburst of 1E 2259+586.

• OSTI ID: 22883172
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 805; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
EMISSION
GAMMA RADIATION
MAGNETIC FIELDS
MONTE CARLO METHOD
NEUTRON STARS
PULSARS
SCATTERING
SPECTRA
SURFACES
THREE-DIMENSIONAL CALCULATIONS
THREE-DIMENSIONAL LATTICES