Quasi-periodic oscillations and broadband variability in short magnetar bursts

Huppenkothen, Daniela and Watts, Anna L. and Uttley, Phil and Van der Horst, Alexander J. and Van der Klis, Michiel and Kouveliotou, Chryssa and Göğüş, Ersin and Granot, Jonathan and Vaughan, Simon and Finger, Mark H. (2013) Quasi-periodic oscillations and broadband variability in short magnetar bursts. Astrophysical Journal, 768 (1). ISSN 0004-637X (Print) 1538-4357 (Online)

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The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and QPOs at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.
Item Type: Article
Additional Information: Article Number: 87
Uncontrolled Keywords: methods: data analysis; methods: statistical; pulsars: individual (SGR 0501+4516); stars: magnetic field; stars: neutron; X-rays: bursts
Subjects: Q Science > QB Astronomy > QB460-466 Astrophysics
Divisions: Faculty of Engineering and Natural Sciences > Basic Sciences > Physics
Faculty of Engineering and Natural Sciences
Depositing User: Ersin Göğüş
Date Deposited: 24 Jul 2013 10:14
Last Modified: 31 Jul 2019 14:43
URI: https://research.sabanciuniv.edu/id/eprint/21725

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