Ten years of INTEGRAL observations of the hard X-ray emission from SGR 1900+14

We exploited the high sensitivity of the INTEGRAL IBIS/ISGRI instrument to study the persistent hard X-ray emission of the soft gamma-ray repeater SGR 1900+14, based on ~11.6 Ms of archival data. The 22-150 keV INTEGRAL spectrum can be well fit by a power law with photon index 1.9 +/- 0.3 and flux F_x = (1.11 +/- 0.17)E-11 erg/cm^2/s (20-100 keV). A comparison with the 20-100 keV flux measured in 1997 with BeppoSAX, and possibly associated with SGR 1900+14, shows a luminosity decrease by a factor of ~5. The slope of the power law above 20 keV is consistent within the uncertainties with that of SGR 1806-20, the other persistent soft gamma-ray repeater for which a hard X-ray emission extending up to 150 keV has been reported.Comment: Accepted for publication in Astronomy & Astrophysics. 4 page

Exact Results on Dynamical Decoupling by π\pi-Pulses in Quantum Information Processes

The aim of dynamical decoupling consists in the suppression of decoherence by appropriate coherent control of a quantum register. Effectively, the interaction with the environment is reduced. In particular, a sequence of $\pi$ pulses is considered. Here we present exact results on the suppression of the coupling of a quantum bit to its environment by optimized sequences of $\pi$ pulses. The effect of various cutoffs of the spectral density of the environment is investigated. As a result we show that the harder the cutoff is the better an optimized pulse sequence can deal with it. For cutoffs which are neither completely hard nor very soft we advocate iterated optimized sequences.Comment: 12 pages and 3 figure

Theoretical aspects of applying sib-pair linkage tests to livestock species

The Haseman-Elston (HE) sib-pair linkage test in its original form is computationally simple but suffers from low power. With the advent of highly polymorphic markers, the exclusive use of fully informative matings (ie matings where the number of genes identical by descent for any sib pair can be inferred without error) for the HE test becomes feasible. This article examines the influence of highly polymorphic marker systems (5 alleles), large family sizes (6 full-sibs) and hierarchical breeding structures (mating ratio of 25) on the power of the HE test by means of simulation studies. Simulations are performed under the assumption that the costs of marker genotyping are a limiting factor for marker-QTL linkage studies. Consequently, the total number of individuals (parents and offspring) typed is fixed at 5 000 in each of the situations compared. The results show that the power of the HE test is considerably increased when both highly polymorphic markers and large full-sib families are available. For example, for a locus explaining 8% of the phenotypic variance the power of the test increases from 14 to 74% if the locus has 5 alleles instead of 2 and sibship size is 6 instead of 2. Hierarchical breeding structures tend to further increase the power of the test, for the example given from 74 to 79%.Dans sa forme originelle, le test de liaison génétique de Haseman-Elston (HE), basé sur les couples de germains, est simple à calculer, mais statistiquement peu puissant. Avec des marqueurs hautement polymorphes, l’utilisation exclusive d’accouplements totalement informatifs (ie des accouplements permettant d’établir avec certitude le nombre de gènes d’origine identique pour n’importe quel couple de germains) peut être envisagée. Cet article examine, à l’aide de simulations, l’effet d’un système génétique hautement polymorphe (5 allèles également fréquents), d’une grande taille de fratrie (6 germains) et d’une structure d’élevage polygynique (25 femelles accouplées à chaque mâle) sur la puissance du test HE. Les simulations sont faites en supposant que le coût des typages génétiques est le facteur limitant des études de liaisons entre gènes marqueurs et locus de caractères quantitatifs. En conséquence, le nombre total d’individus typés (parents et descendants) est fixé à 5 000 dans chacune des situations comparées. Les résultats montrent que la puissance du test HE est considérablement accrue quand on dispose à la fois de marqueurs hautement polymorphes et de grandes fratries. Ainsi, pour un locus expliquant 8% de la variance phénotypique du caractère, la puissance du test au seuil de 5% est de 0,74 au lieu de 0, 14 quand on passe de 2 à 5 allèles au locus marqueur et de 2 à 6 frères par fratrie. Les structures d’élevage-polygyniques tendent à accroître encore la puissance du test, qui, dans l’exemple ci-dessus, passe de 0,74 à 0,79 avec une structure de 25 fratries issues du même père, par rapport à des couples de parents indépendants

Generic susceptibilities of the half-filled Hubbard model in infinite dimensions

Around a metal-to-insulator transition driven by repulsive interaction (Mott transition) the single particle excitations and the collective excitations are equally important. Here we present results for the generic susceptibilities at zero temperature in the half-filled Hubbard model in infinite dimensions. Profiting from the high resolution of dynamic density-matrix renormalization at all energies, results for the charge, spin and Cooper-pair susceptibilities in the metallic and the insulating phase are computed. In the insulating phase, an almost saturated local magnetic moment appears. In the metallic phase a pronounced low-energy peak is found in the spin response.Comment: 12 pages, 12 figures; slight changes and one additional figure due to referees' suggestion

Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910

Previous studies of the X-ray flux and spectral properties of 1RXS J170849-400910 showed hints of a possible correlation with the spin glitches that occurred in 1999 and 2001. However, due to the sparseness of spectral measurements and the paucity of detected glitches no firm conclusion could be drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910 covering the time interval between January 2003 and June 2006 and carried out a detailed timing analysis by means of phase fitting techniques. We detected two relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in January and June 2005. Interestingly, the occurrence times of these glitches are in agreement with the predictions made in our previous studies. This finding strongly suggests a connection between the flux, spectral and timing properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The Neutron Star Crust and Surface: Observations and Models" on June 27; referee comments adde

Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL

We report on a multi-band high-energy observing campaign aimed at studying the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS J170849.0-400910, one of the magnetar candidates. We observed 1RXS J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy range. Furthermore, we also reanalyzed, using the latest calibration and software, all the publicly available INTEGRAL data since 2002, and the soft X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and Swift/XRT, in order to study the soft and hard X-ray spectral variability of 1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux, extending the hardness-intensity correlation proposed for this source over 2 orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy & Astrophysics main journa

Self-consistent spin-wave theory for a frustrated Heisenberg model with biquadratic exchange in the columnar phase and its application to iron pnictides

Recent neutron scattering studies revealed the three dimensional character of the magnetism in the iron pnictides and a strong anisotropy between the exchange perpendicular and parallel to the spin stripes. We extend studies of the J1-J2-Jc Heisenberg model with S = 1 using self-consistent spin-wave theory. A discussion of two scenarios for the instability of the columnar phase is provided. The relevance of a biquadratic exchange term between in-plane nearest neighbors is discussed. We introduce mean-field decouplings for biquadratic terms using the Dyson-Maleev and the Schwinger boson representation. Remarkably their respective mean-field theories do not lead to the same results, even at zero temperature. They are gauged in the N'eel phase in comparison to exact diagonalization and series expansion. The J1-J2-Jc model is analyzed under the influence of the biquadratic exchange Jbq and a detailed description of the staggered magnetization and of the magnetic excitations is given. The biquadratic exchange increases the renormalization of the in-plane exchange constants which enhances the anisotropy between the exchange parallel and perpendicular to the spin stripes. Applying the model to iron pnictides, it is possible to reproduce the spin-wave dispersion for CaFe2As2 in the direction perpendicular to the spin stripes and perpendicular to the planes. Discrepancies remain in the direction parallel to the spin stripes which can be resolved by passing from S = 1 to S = 2. In addition, results for the dynamical structure factor within the self-consistent spin-wave theory are provided.Comment: 18 pages, 12 figures. Updated version, several references adde