Shear Waves and Giant Flare Oscillations from Soft Gamma-ray Repeaters
نویسنده
چکیده
Recent observations of giant flares from soft gamma-ray repeaters have exhibited multiple ∼ 25 − 150 Hz oscillations. Frequencies in this range are expected for toroidal shear waves in a neutron star (NS) crust, lending support to Duncan’s proposal that such modes may be excited in these events. This motivates a reassessment of how these waves reflect the NS structure and what role the magnetic field plays in setting their frequencies. We calculate the eigenfrequencies and eigenfunctions of toroidal oscillations for a realistic NS crust, including a vertical magnetic field at magnetar strengths (B ∼ 1014 − 1015 G). The lowest radial-order mode has a redshifted frequency of ≈ 28 Hz[l(l + 1)/6]1/2, with the prefactor depending on the NS’s mass and radius, and its crust’s depth and composition. This mode is independent of the magnetic field for B . 4× 1015 G, a limit much greater than the inferred dipole magnetic fields for these objects. Though this is a good fit to the observed oscillations, only rather loose constraints can be made for the NSs’ properties because all that can be fit is this prefactor (a single parameter). Modes with shorter radial wavelengths are more sensitive to the magnetic field starting at B ∼ 2× 1014 G and have higher frequencies (∼ 600 − 2000 Hz). The discovery of these modes, coupled with the oscillations observed thus far, would provide a powerful probe to the NS crustal structure. Subject headings: gamma rays: bursts — stars: magnetic fields— stars: neutron — stars: oscillations
منابع مشابه
Magnetars ’ Giant Flares : the case of SGR 1806 - 20
We first review on the peculiar characteristics of the bursting and flaring activity of the Soft Gamma-ray Repeaters and Anomalous Xray Pulsars. We then report on the properties of the SGR 1806-20’s Giant Flare occurred on 2004 December 27th, with particular interest on the pre and post flare intensity/hardness correlated variability. We show that these findings are consistent with the picture ...
متن کاملHigh frequency oscillations during magnetar flares
The recent discovery of high frequency oscillations during giant flares from the Soft Gamma Repeaters SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. We review the observational da...
متن کاملOn the Possibility of Identification of a Short/Hard Burst GRB 051103 with the Giant Flare from a Soft Gamma Repeater in the M81 Group of Galaxies
The light curve, energy characteristics, and localization of a short/hard GRB 051103 burst are considered. Evidence in favor of identifying this event with a giant flare from a soft gamma repeater in the nearby M81 group of interacting galaxies is discussed. Subject headings: Gamma repeaters, giant flares, galaxies
متن کاملDo soft gamma repeaters emit gravitational waves ?
Soft gamma repeaters are identified as highly magnetized (B≈ 10 14 Gauss) neutron stars. Magnetic stresses induce tectonic activity, and field annihilation in faults is the ultimate energy source for the observed γ-ray emission. As a consequence of the crustal cracking, the stored elastic energy is converted into high frequency (kHz) shear waves, that excite nonradial oscillation modes damped b...
متن کاملDo Soft Gamma Repeaters Emit Gravitational Waves ?
Soft gamma repeaters are identified as highly magnetized (B≈ 10 14 Gauss) neutron stars. Magnetic stresses induce tec-tonic activity, and field annihilation in faults is the ultimate energy source for the observed γ-ray emission. As a consequence of the crustal cracking, the stored elastic energy is converted into high frequency (kHz) shear waves, that excite nonradial oscillation modes damped ...
متن کامل