Relativistic Jets from X-ray binaries

In this review I summarise the status of observational research into relativistic jets from X-ray binaries, highlighting four areas in particular: (i) How relativistic are the jets ?, (ii) The disc : jet coupling, (iii) the nature of the underlying flat spectral component, and (iv) the relation between jets from black holes and those from neutron stars. I have attempted to discuss the extent of our (limited) physical understanding, and to point the way towards relevant new observational tests of the various phenomena.Comment: Review article, to be published in `Astrophysics and Cosmology : A collection of critical thoughts', Springer Lecture Notes in Physic

Supersoft X-Ray Sources in M31

The nearby Andromeda galaxy (M31) has been observed with the ROSAT PSPC in a mosaic of 6 pointings with 25 ksec each. In the paper describing the results on the total sample of detected sources, Supper et al. (1996) also report the positions for 15 supersoft X-ray sources and the blackbody fit results for the brightest of these sources. We report here in more detail on the X-ray spectral characteristics of all these 15 supersoft X-ray sources. Optical multi-colour photometric data obtained in 1990 at the Michigan- Dartmouth-MIT Observatory at Kitt Peak were used originally in the selection process of the supersoft sources, and are the basis for the finding charts given here for most selected X-ray sources.Comment: 8 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996

String order in spin liquid phases of spin ladders

Two-leg spin ladders have a rich phase diagram if rung, diagonal and plaquette couplings are allowed for. Among the possible phases there are two Haldane-type spin liquid phases without local order parameter, which differ, however, in the topology of the short range valence bonds. We show that these phases can be distinguished numerically by two different string order parameters. We also point out that long range string- and dimer orders can coexist

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

Identifying conservation units after large-scale land clearing: a spatio-temporal molecular survey of endangered white-tailed black cockatoos (Calyptorhynchus spp.)

Aim: We examined how the threatened and endemic white-tailed black cockatoos of Western Australia have responded genetically to recent and comprehensive habitat loss with the ultimate aim of identifying units for conservation. We assessed the population structure, connectivity and genetic diversity at spatial and temporal scales for Calyptorhynchus baudinii and C. latirostris, which have undergone dramatic population declines. Genetic comparisons of pre- and post-population decline were carried out by including historical samples dating back to 1920. We examined samples collected from across 700 km of their distribution and sampled approximately 1% of the current population census size to produce significant insights into the population genetics of white-tailed black cockatoos and generate genetic information crucial for conservation management. Location: Southwest corner of Western Australia. Methods: Six hundred and eighty-four cockatoo samples were collected from 1920 to 2010 and profiled with 19 microsatellites to identify spatial population structure and loss of genetic diversity.Results: The temporal and spatial microsatellite data illustrated that the geographically defined genetic structuring in white-tailed black cockatoos is likely to represent a recent phenomenon. We identified: (1) spatial population substructure east and west of extensively cleared habitat (>95,800 km2), but the historical samples clustered with the current western population, regardless of origin, (2) a regional loss of allelic diversity over 3–4 generations for the current eastern population, (3) a lack of a genetic signal of the recent population decline, but perhaps a mid-Holocene population collapse and lastly, (4) limited genetic differentiation between the two currently recognized white-tailed black-cockatoo species suggests a review of taxonomy and/or management units should be undertaken. Main conclusion: Based on extensive spatio-temporal sampling, we have demonstrated that recent anthropogenic habitat modifications have affected the genetic structure of a long-lived and highly mobile species. Our results have identified areas of high conservation value and the importance of maintaining native vegetation migration corridors

The Hubbard model with smooth boundary conditions

We apply recently developed smooth boundary conditions to the quantum Monte Carlo simulation of the two-dimensional Hubbard model. At half-filling, where there is no sign problem, we show that the thermodynamic limit is reached more rapidly with smooth rather than with periodic or open boundary conditions. Away from half-filling, where ordinarily the simulation cannot be carried out at low temperatures due to the existence of the sign problem, we show that smooth boundary conditions allow us to reach significantly lower temperatures. We examine pairing correlation functions away from half-filling in order to determine the possible existence of a superconducting state. On a $10\times 10$ lattice for $U=4$, at a filling of $\langle n \rangle = 0.87$ and an inverse temperature of $\beta=10$, we did find enhancement of the $d$-wave correlations with respect to the non-interacting case, a possible sign of $d$-wave superconductivity.Comment: 16 pages RevTeX, 9 postscript figures included (Figure 1 will be faxed on request

Superconductivity in quantum-dot superlattices composed of quantum wire networks

Based on calculations using the local density approximation, we propose quantum wire networks with square and plaquette type lattice structures that form quantum dot superlattices. These artificial structures are well described by the Hubbard model. Numerical analysis reveals a superconducting ground state with transition temperatures $T_c$ of up to 90 mK for the plaquette, which is more than double the value of 40 mK for the square lattice type and is sufficiently high to allow for the experimental observation of superconductivity.Comment: 10 pages, 4 figure

Anomalous behaviors of the charge and spin degrees of freedom in the CuO double chains of PrBa2_2Cu4_4O8_8

The density-matrix renormalization-group method is used to study the electronic states of a two-chain Hubbard model for CuO double chains of PrBa$_2$Cu$_4$O$_8$. We show that the model at quarter filling has the charge ordered phases with stripe-type and in-line--type patterns in the parameter space, and in-between, there appears a wide region of vanishing charge gap; the latter phase is characteristic of either Tomonaga-Luttinger liquid or a metallic state with a spin gap. We argue that the low-energy electronic state of the CuO double chains of PrBa$_2$Cu$_4$O$_8$ should be in the metallic state with a possibly small spin gap.Comment: REVTEX 4, 10 pages, 9 figures; submitted to PR

Hybridization-induced superconductivity from the electron repulsion on a tetramer lattice having a disconnected Fermi surface

Plaquette lattices with each unit cell containing multiple atoms are good candidates for disconnected Fermi surfaces, which are shown by Kuroki and Arita to be favorable for spin-flucutation mediated superconductivity from electron repulsion. Here we find an interesting example in a tetramer lattice where the structure within each unit cell dominates the nodal structure of the gap function. We trace its reason to the way in which a Cooper pair is formed across the hybridized molecular orbitals, where we still end up with a T_c much higher than usual.Comment: 4 pages, 6 figure