# Search for periodic signals in magnetar giant flares

## Bayesian inspection of SGR 1806-20 and SGR 1900+14

### 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 D3PO. The D3PO algorithm
models the raw photon counts as a continuous flux and takes
care of the Poissonian shot noise as well as all instrument
effects. 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 ν > 17 Hz,
because they fall into the noise dominated regime. However, we find
two new candidates for oscillations at 9.2 Hz (SGR 1806-20) and
7.7 Hz (SGR 1900+14). Assuming these to be the fundamental
magneto-elastic oscillations of the magnetars, current
theoretical models favour relatively weak magnetic fields
B ̄ ∼ 6 × 1013 − 3 × 1014 G (SGR 1806-20) and a
relatively small shear velocity inside the crust compared to previous findings.

Below you may download of the results of our reconstruction.

In the .txt-files you may find the reconstructed light curve and power spectrum of SGR 1806-20 and SGR 1900+14, using two different smoothness enforcing prior.

For all reconstructions we used a regular grid. Each pixel in the time domain has volume of 1/800 s and its harmonic domain 1/655 Hz.

The interactive plot allows you to zoom into specific regions of interest.

Daniel Pumpe

Michael Gabler

Max Planck Institute for Astrophysics

Karl Schwarzschild Straße 1

80741 Garching

Germany

e-mail:

dpumpe@MPA-Garching.MPG.DE

miga@MPA-Garching.MPG.DE

Page last updated on 2017-08-16.