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

Abstract

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 1806Ϫ20. 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.

Bayesian timing analysis of giant flare of SGR 180620 by RXTE PCA

“…The Bayesian posterior probability density vs. trial frequency of the periodic signal for the giant flare data set of SGR 1806−20. QPO frequencies already detected by averaged power spectrum analysis and also with other mission RHESSI (Israel et al 2005;) are marked as small lines at the top axis. Those QPO frequencies are also detected by us.…”

“…Bretthorst 1988). In the previous timing analysis of the giant flare data set of SGR 1806−20 by Israel et al (2005) and , an averaged power spectrum was considered. Namely, for each rotational cycle or certain rotational phase interval of SGR 1806−20 an independent classical power spectrum was determined that depends on the phase of rotation and decaying tail of the giant flare, which were subsequently co-added and averaged.…”

Pulsars and Magnetars

“…Quasi periodic oscillations (QPOs) were discovered in the giant flare of SGR 1806−20 [93]. This prompted a re-analysis of the data available for the previous giant flares and the same phenomenon was found in SGR 1900+14 [171].…”

Discovery of X-ray pulsations from a massive star

“…It is illuminating to compare x 1 CMa with the degenerate X-ray pulsars, namely white dwarfs and neutron stars [63][64][65] . Some neutron star X-ray pulsars have a thermal component in their X-ray spectra, which is explained as originating from their atmosphere 66 .…”