Search for quasi-periodic signals in magnetar giant flares

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 $\nu\gtrsim17\,$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 $\bar B\sim 6\times10^{13} - 3\times10^{14}\,$G (SGR 1806-20) and a relatively low shear velocity inside the crust compared to previous findings

Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube

We report on nonlinear cotunneling spectroscopy of a carbon nanotube quantum dot coupled to Nb superconducting contacts. Our measurements show rich subgap features in the stability diagram which become more pronounced as the temperature is increased. Applying a transport theory based on the Liouville-von Neumann equation for the density matrix, we show that the transport properties can be attributed to processes involving sequential as well as elastic and inelastic cotunneling of quasiparticles thermally excited across the gap. In particular, we predict thermal replicas of the elastic and inelastic cotunneling peaks, in agreement with our experimental results.Comment: 21 pages, 9 figures, submitted to New Journal of Physic

Temperature dependence of Andreev spectra in a superconducting carbon nanotube quantum dot

Tunneling spectroscopy of a Nb coupled carbon nanotube quantum dot reveals the formation of pairs of Andreev bound states (ABS) within the superconducting gap. A weak replica of the lower ABS is found, which is generated by quasi-particle tunnelling from the ABS to the Al tunnel probe. An inversion of the ABS-dispersion is observed at elevated temperatures, which signals the thermal occupation of the upper ABS. Our experimental findings are well supported by model calculations based on the superconducting Anderson model.Comment: 6 pages, 7 figure

On the absence of fifth-order contributions to the nucleon mass in heavy-baryon chiral perturbation theory

(New version with some expanded discussion; figures and minor typos corrected.) We have calculated the contribution proportional to the fifth power of the pion mass in the chiral expansion of the nucleon mass in two flavour HBCPT. Only one irreducible two-loop integral enters, and this vanishes. All other corrections in the heavy-baryon limit can be absorbed in the physical pion-nucleon coupling constant which enters in the third order term, and so there are no contributions at fifth order. Including finite nucleon mass corrections, the only contribution agrees with the expansion of the relativistic one-loop graph in powers of the ration of the pion and nucleon masses, and is only 0.3% of the third order term. This is an encouraging result for the convergence of two-flavour heavy-baryon chiral perturbation theory.Comment: 4 pages RevTex, 4 eps figure

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

We studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint