Discovery of Quasi-Periodic Oscillations in the Recurrent Burst Emission from SGR 1806-20

Abstract

We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within $\sim$ 1$\sigma$ from the 92 Hz QPO detected in the giant flare. The third QPO lie within $\sim$ 9$\sigma$ from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations, which set a lower limit confidence interval $\ge 4.3\sigma$. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our finding against the available theoretical models and discuss the connection between the QPOs we report and those detected in the giant flares. The implications to the neutron star properties are also discussed.

arXiv comment5 pages, 2 figures, Accepted for publication in the Astrophysical Journal Letters (ApJL)

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Cited by in corpus (9)

• Magneto-elastic oscillations of neutron stars with dipolar magnetic fields
• Quasi-Periodic Oscillations in Short Recurring Bursts of the Soft-Gamma Repeater J1550-5418
• On the excitation of f-modes and torsional modes by magnetar giant flares
• Quasi-Periodic Oscillations and broadband variability in short magnetar bursts
• Quasi-Periodic Oscillations in Short Recurring Bursts of the magnetars SGR 1806-20 and SGR 1900+14 Observed With RXTE
• Torsional Oscillations of a Magnetar with a Tangled Magnetic Field
• Electromagnetic fields in the exterior of an oscillating relativistic star -- II. Electromagnetic damping
• Detecting Long-Duration Narrow-Band Gravitational Wave Transients Associated with Soft Gamma Repeater Quasi-Periodic Oscillations
• Properties of strongly magnetized ultradense matter and their imprints on magnetar pulsations