Years of RXTE Monitoring of Anomalous X-ray Pulsar 4U 0142+61: Long-Term Variability

We report on 10 years of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 March until 2006 February: the RMS phase residual for a spin-down model which includes nu, nudot, and nuddot is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch may have occured between 1998 and 2000, but is not required by the existing timing data. The pulse profile has been evolving since 2000. In particular, the dip of emission between its two peaks got shallower between 2002 and 2006, as if the profile were evolving back to its pre-2000 morphology, following an earlier event, which possibly also included the glitch suggested by the timing data. These profile variations are seen in the 2-4 keV band but not in 6-8 keV. We also detect a slow increase in the pulsed flux between 2002 May and 2004 December, such that it has risen by 36+/-3% over 2.6 years in the 2-10 keV band. The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar model.Comment: 28 pages, 8 figures, accepted by Ap

reentrance effect in normal-metal/superconducting hybrid loops

We have measured the transport properties of two mesoscopic hybrid loops composed of a normal-metal arm and a superconducting arm. The samples differed in the transmittance of the normal/superconducting interfaces. While the low transmittance sample showed monotonic behavior in the low temperature resistance, magnetoresistance and differential resistance, the high transmittance sample showed reentrant behavior in all three measurements. This reentrant behavior is due to coherent Andreev reflection at the normal/superconducting interfaces. We compare the reentrance effect for the three different measurements and discuss the results based on the theory of quasiclassical Green's functions

The signature of 44Ti in Cassiopeia A revealed by IBIS/ISGRI on INTEGRAL

We report the detection of both the 67.9 and 78.4 keV 44Sc gamma-ray lines in Cassiopeia A with the INTEGRAL IBIS/ISGRI instrument. Besides the robustness provided by spectro-imaging observations, the main improvements compared to previous measurements are a clear separation of the two 44Sc lines together with an improved significance of the detection of the hard X-ray continuum up to 100 keV. These allow us to refine the determination of the 44Ti yield and to constrain the nature of the nonthermal continuum emission. By combining COMPTEL, BeppoSAX/PDS and ISGRI measurements, we find a line flux of (2.5 +/- 0.3)*10(-5) cm(-2) s(-1) leading to a synthesized 44Ti mass of 1.6 (+0.6-0.3)*10(-4) solar mass. This high value suggests that Cas A is peculiar in comparison to other young supernova remnants, from which so far no line emission from 44Ti decay has been unambiguously detected.Comment: 5 pages, 4 figures, Accepted for publication in ApJ

The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays

For the first time a quasi-simultaneous multi-wavelength campaign has been performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band. 4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these observations it was also observed in the X-ray band with Swift and RXTE, in the optical and NIR with Gemini North and in the radio with the WSRT. In this paper we present the source-energy distribution. The spectral results obtained in the individual wave bands do not connect smoothly; apparently components of different origin contribute to the total spectrum. Remarkable is that the INTEGRAL hard X-ray spectrum (power-law index 0.79 +/- 0.10) is now measured up to an energy of ~230 keV with no indication of a spectral break. Extrapolation of the INTEGRAL power-law spectrum to lower energies passes orders of magnitude underneath the NIR and optical fluxes, as well as the low ~30 microJy (2 sigma) upper limit in the radio band.Comment: 6 pages, 1 figure. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. S. Zane, R. Turolla and D. Pag

Radiolysis of NaCl at high and low temperatures: development of size distribution of bubbles and colloids

New experimental results are presented on low temperature irradiation (18 °C) of rock-salt samples which had been exposed to initial doses up to 320 GRad at 100 °C. Differential scanning calorimetry (DSC) shows that the latent heat of melting (LHM) of sodium colloids decreases during subsequent low-temperature irradiation, whereas the stored energy (SE) increases slowly, indicating that the process of radiolysis continues. The decrease of the LHM is due to dissolution of large colloids, because the intensities of the melting peaks decrease during the second stage irradiation at low temperature. The model is formulated to describe the nucleation kinetics and the evolution of the size distribution of chlorine precipitates and sodium colloids in NaCl under high dose irradiation. It is shown that the mechanism of dissolution of large Na colloids during low temperature irradiation can be related to melting of sodium colloids.

Superconducting Proximity Effect and Universal Conductance Fluctuations

We examine universal conductance fluctuations (UCFs) in mesoscopic normal-superconducting-normal (N-S-N) structures using a numerical solution of the Bogoliubov - de Gennes equation. We discuss two cases depending on the presence (``open'' structure) or absence (``closed'' structure) of quasiparticle transmission. In contrast to N-S structures, where the onset of superconductivity increases fluctuations, we find that UCFs are suppressed by superconductivity for N-S-N structures. We demonstrate that the fluctuations in ``open'' and ``closed'' structures exhibit distinct responses to an applied magnetic field and to an imposed phase variation of the superconducting order parameter.Comment: (4 pages, 5 figures). Corrected typos in equations, added references, changed Fig. 5 and its discussions. Phys. Rev. B, accepted for publicatio

Experimental determination of the quasi-particle decay length ξSm\xi_{\text{Sm}} in a superconducting quantum well

We have investigated experimentally the electronic transport properties of a two-dimensional electron gas (2DEG) present in an AlSb/InAs/AlSb quantum well, where part of the toplayer has been replaced by a superconducting Nb strip, with an energy gap $\Delta_0$. By measuring the lateral electronic transport underneath the superconductor, and comparing the experimental results with a model based on the Bogoliubov-de Gennes equation and the Landauer-B\"uttiker formalism, we obtain a decay length $\xi_{\text{Sm}} \approx 100~\text{nm}$ for electrons. This decay length corresponds to an interface transparency $T_{\text{SIN}}=0.7$ between the Nb and InAs. Using this value, we infer an energy gap in the excitation spectrum of the SQW of $\Delta_{\text{eff}} = 0.97 \Delta_0 = 0.83~\text{meV}$.Comment: Revtex, 3 PostScript figure

Re-entrance of the metallic conductance in a mesoscopic proximity superconductor

We present an experimental study of the diffusive transport in a normal metal near a superconducting interface, showing the re-entrance of the metallic conductance at very low temperature. This new mesoscopic regime comes in when the thermal coherence length of the electron pairs exceeds the sample size. This re-entrance is suppressed by a bias voltage given by the Thouless energy and can be strongly enhanced by an Aharonov Bohm flux. Experimental results are well described by the linearized quasiclassical theory.Comment: improved version submitted to Phys. Rev. lett., 4 pages, 5 included epsf figure