The Discovery of Rapid X-Ray Oscillations in the Tail of the SGR 1806–20 Hyperflare

By G. Israel, T. Belloni, L. Stella, Y. Rephaeli, D. Gruber, P. Casella, S. Dall’Osso, N. Rea, M. Persic, R. Rothschild. 2005

247 citations recorded by the source corpus.

We have discovered rapid quasi-periodic oscillations (QPOs) in RXTE/PCA measurements of the pulsating tail of the 2004 December 27 giant flare of SGR 1806-20. QPOs at ~92.5 Hz are detected in a 50 s interval starting 170 s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ~18 and ~30 Hz are also detected ~200-300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a soft gamma-ray repeater or any other magnetar candidate. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfvén waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the magnetar.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/177d448f71f394dc10d334925c60ccd552a020f8

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. P. Lasky
2. A. Watts
3. T. Strohmayer
4. N. Andersson
5. L. Samuelsson
6. Sandro Mereghetti
7. J. Lattimer

In Geophysics

1. A. Watts
2. P. Lasky
3. N. Andersson
4. L. Samuelsson
5. T. Strohmayer

Citations in the corpus

• Neutron star asteroseismology. Axial crust oscillations in the Cowling approximation (2006, methodology): “It may, for instance, be noted in table 1 that we arrive at a different multipole identification compared to Strohmayer & Watts (2005) for SGR 1900+14 and Israel et al. (2005) for SGR 1806−20.”
• The 2004 Hyperflare from SGR 1806–20: Further Evidence for Global Torsional Vibrations (2006, methodology): “…have shown the ≈ 90 Hz QPO to be extremely robust, and its approximate location in rotational phase has been linked to the interpulse region, by both Israel et al. (2005) and Watts & Strohmayer (2006), we began our study by computing average power spectra around this phase range, but for a…”
• Discovery of Fast X-Ray Oscillations during the 1998 Giant Flare from SGR 1900+14 (2005, background): “Israel et al. (2005) conjectured that toroidal oscillations of the neutron star might explain the observed frequencies.”
• Detection with RHESSI of High-Frequency X-Ray Oscillations in the Tailof the 2004 Hyperflare from SGR 1806–20 (2005, methodology): “Using the significance quoted by Israel et al. (2005), we can compute the probability of getting two apparent detections at the same frequency, time and phase, due to noise alone, given the number of trials.”
• Gravitational Waves from Neutron Stars: A Review (2015, background): “Observations of quasi-periodic oscillations (QPOs) in the tails of two giant flares (Israel et al. 2005; Strohmayer & Watts 2005) has engendered excitement about the potential new field of neutron star asteroseismology.”