http://arxiv.org/abs/1708.05702
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 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 $\nu\gtrsim17\,$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 $\bar B\sim 6\times10^{13} – 3\times10^{14}\,$G (SGR 1806-20) and a relatively small shear velocity inside the crust compared to previous findings.
D. Pumpe, M. Gabler, T. Steininger, et. al.
Mon, 21 Aug 17
40/44
Comments: N/A