Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8141479 | New Astronomy | 2016 | 7 Pages |
Abstract
Quasi-periodic oscillations (QPOs) discovered in soft-gamma repeaters (SGRs) are expected to help us to study the properties of matter in neutron stars. In earlier investigations, we identified the QPOs of frequencies below â¼100 Hz observed in giant flares of SGR 1806â20 and SGR 1900+14 as the crustal torsional oscillations. For this purpose, we calculated the frequencies of the fundamental torsional oscillations with various angular indices â, by changing the stellar mass and radius. In this work, we try to explain the additional QPO frequencies recently reported by Huppenkothen et al. (2014a, 2014b) within the same framework as before except that we newly take into account the effect of electron screening, which acts to decrease the frequencies by a small amount. Those QPOs were discovered in two different SGRs, i.e., SGR 1806â20 and SGR J1550â5418. Then, we find that the newly observed QPO frequency in SGR 1806â20 can be still identified as one of the frequencies of the fundamental torsional oscillations, while those in SGR J1550â5418 can also be explained in terms of the torsional oscillations although the relevant angular indices are difficult to identify.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Astronomy and Astrophysics
Authors
Hajime Sotani, Kei Iida, Kazuhiro Oyamatsu,