Search for quasi-periodic signals in magnetar giant flares

Abstract

Quasi-periodic oscillations (QPOs) discovered in the decaying tails of giant flares of magnetars are believed to be torsional oscillations of neutron stars. These QPOs have a high potential to constrain properties of high-density matter. In search for quasi-periodic signals, we study the light curves of the giant flares of SGR 1806-20 and SGR 1900+14, with a non-parametric Bayesian signal inference method called D${}^3$PO. The D${}^3$PO algorithm models the raw photon counts as a continuous flux and takes the Poissonian shot noise as well as all instrument effects into account. It reconstructs the logarithmic flux and its power spectrum from the data. Using this fully noise-aware method, we do not confirm previously reported frequency lines at $\nu \gtrsim 17$Hz because they fall into the noise-dominated regime. However, we find two new potential candidates for oscillations at $9.2$Hz (SGR 1806-20) and $7.7$Hz (SGR 1900+14). If these are real and the fundamental magneto-elastic oscillations of the magnetars, current theoretical models would favour relatively weak magnetic fields $\bar{B}\sim 6\times 10^{13}-3\times 10^{14}$G (SGR 1806-20) and a relatively low shear velocity inside the crust compared to previous findings.

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Cited by in corpus (15)

• The Galactic Faraday depth sky revisited
• Constraints on the nuclear equation of state and the neutron star structure from crustal torsional oscillations
• Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations
• On the Persistence of QPOs During the SGR 1806-20 Giant Flare
• Evidence for a strong 19.5 Hz flux oscillation in Swift BAT and Fermi GBM gamma-ray data from GRB 211211A
• Denoising, deconvolving and decomposing multi-domain photon observations- The D4PO algorithm
• Tangled magnetic field model of QPOs
• Torsional oscillations of magnetized neutron stars with mixed poloidal-toroidal fields
• Zeeman splitting of torsional oscillation frequencies of magnetars
• Selfsimilarity relations for torsional oscillations of neutron stars
• Powerful flares and magneto-elastic oscillations of magnetars
• Separating diffuse from point-like sources - a Bayesian approach
• Misidentification of Short GRBs as Magnetars in Nearby Galaxies
• Zeeman effect in oscillations of magnetars with toroidal magnetic fields
• Nonlinear coupling between magnetar QPOs