INTEGRAL/RossiXTE high-energy observation of a state transition of GX 339-4

On 2004 August 15, we observed a fast (shorter than 10 hours) state transition in the bright black-hole transient GX 339-4 simultaneously with RossiXTE and INTEGRAL. This transition was evident both in timing and spectral properties. Combining the data from PCA, HEXTE and IBIS, we obtained good quality broad-band (3-200 keV) energy spectra before and after the transition. These spectra indicate that the hard component steepened. Also, the high-energy cutoff that was present at ~70 keV before the transition was not detected after the transition. This is the first time that an accurate determination of the broad-band spectrum across such a transition has been measured on a short time scale. It shows that, although some spectral parameters do not change abruptly through the transition, the high-energy cutoff increases/disappears rather fast. These results constitute a benchmark on which to test theoretical models for the production of the hard component in these systems.Comment: Accepted for publication in MNRAS (9 pages, 6 figures

Decay process accelerated by tunneling in its very early stage

We examine a fast decay process that arises in the transition period between the Gaussian and exponential decay processes in quantum decay systems. It is usually expected that the decay is decelerated by a confinement potential barrier. However, we find a case where the decay in the transition period is accelerated by tunneling through a confinement potential barrier. We show that the acceleration gives rise to an appreciable effect on the time evolution of the nonescape probability of the decay system.Comment: 4 pages, 6 figures; accepted for publication in Phys. Rev.

Hamiltonian dynamics of homopolymer chain models

The Hamiltonian dynamics of chains of nonlinearly coupled particles is numerically investigated in two and three dimensions. Simple, off-lattice homopolymer models are used to represent the interparticle potentials. Time averages of observables numerically computed along dynamical trajectories are found to reproduce results given by the statistical mechanics of homopolymer models. The dynamical treatment, however, indicates a nontrivial transition between regimes of slow and fast phase space mixing. Such a transition is inaccessible to a statistical mechanical treatment and reflects a bimodality in the relaxation of time averages to corresponding ensemble averages. It is also found that a change in the energy dependence of the largest Lyapunov exponent indicates the theta-transition between filamentary and globular polymer configurations, clearly detecting the transition even for a finite number of particles.Comment: 11 pages, 8 figures, accepted for publication in Physical Review

A turbulence-driven model for heating and acceleration of the fast wind in coronal holes

A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upwards in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvenic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data.Comment: accepted for publication in ApJ

On the diagonalization of the discrete Fourier transform

The discrete Fourier transform (DFT) is an important operator which acts on the Hilbert space of complex valued functions on the ring Z/NZ. In the case where N=p is an odd prime number, we exhibit a canonical basis of eigenvectors for the DFT. The transition matrix from the standard basis to the canonical basis defines a novel transform which we call the discrete oscillator transform (DOT for short). Finally, we describe a fast algorithm for computing the discrete oscillator transform in certain cases.Comment: Accepted for publication in the journal "Applied and Computational Harmonic Analysis": Appl. Comput. Harmon. Anal. (2009), doi:10.1016/j.acha.2008.11.003. Key words: Discrete Fourier Transform, Weil Representation, Canonical Eigenvectors, Oscillator Transform, Fast Oscillator Transfor

A Radiative Cycle with Stimulated Emission from Atoms (Ions) in an astrophysical Plasma

We propose that a radiative cycle operates in atoms (ions) located in a rarefied gas in the vicinity of a hot star. Besides spontaneous transitions the cycle includes a stimulated transition in one very weak intermediate channel. This radiative "bottle neck" creates a population inversion, which for an appropriate column density results in amplification and stimulated radiation in the weak transition. The stimulated emission opens a fast decay channel leading to a fast radiative cycle in the atom (or ion). We apply this model by explaining two unusually bright Fe II lines at 250.7 and 250.9 nm in the UV spectrum of gas blobs close to h Carinae, one of the most massive and luminous stars in the Galaxy. The gas blobs are spatially resolved from the central star by the Hubble Space Telescope (HST). We also suggest that in the frame of a radiative cycle stimulated emission is a key phenomenon behind many spectral lines showing anomalous intensities in spectra of gas blobs outside eruptive stars.Comment: Accepted for publication in Phys. Rev. Letter

The Influence of Magnetic Field on Oscillations in the Solar Chromosphere

Two sequences of solar images obtained by the Transition Region and Coronal Explorer in three UV passbands are studied using wavelet and Fourier analysis and compared to the photospheric magnetic flux measured by the Michelson Doppler Interferometer on the Solar Heliospheric Observatory to study wave behaviour in differing magnetic environments. Wavelet periods show deviations from the theoretical cutoff value and are interpreted in terms of inclined fields. The variation of wave speeds indicates that a transition from dominant fast-magnetoacoustic waves to slow modes is observed when moving from network into plage and umbrae. This implies preferential transmission of slow modes into the upper atmosphere, where they may lead to heating or be detected in coronal loops and plumes.Comment: 8 pages, 6 figures (4 colour online only), accepted for publication in The Astrophysical Journa