Pulsars, transients and relativistic astrophysics

Abstract:

We were recently faced with the following problem: The T-shaped Plateau de Bure Interferometer is expanding its tracks to achieve higher spatial resolution in astronomical images at mm wavelengths. Two more stations for positioning the antennas during observations are being built at the ends of the extended tracks. Which of the given stations should the remaining four antennas occupy to accommodate the new stations? What is the optimal set of antenna configurations, given the new extended one, to achieve necessary coverage of the uv-plane at a variety of spatial resolutions? We present in this paper the solutions to the above questions, resulting from a novel method we have recently developed. The method is based on identifying which placement of elements provides the most appropriate uv-plane sampling. © 2006 American Institute of Physics.

Abstract:

We present an exact three-dimensional wave solution to the shearing-sheet equations of motion. The existence of this solution argues against transient amplification as a route to turbulence in unmagnetized disks. Moreover, because the solution covers an extensive dynamical range in wavenumber space, it is an excellent test of the dissipative properties of numerical codes. © 2006. The American Astronomical Society. All rights reserved.

Abstract:

We present results of a multi-wavelength program to study the faint discrete X-ray source population discovered by Chandra in the Galactic Centre (GC). From IR imaging obtained with the VLT we identify candidate K-band counterparts to 75% of the X-ray sources in our sample. By combining follow-up VLT K-band spectroscopy of a subset of these candidate counterparts with the magnitude limits of our photometric survey, we suggest that only a small percentage of the sources are HMXBs, while the majority are likely to be canonical LMXBs and CVs at the distance of the GC. In addition, we present our discovery of highly structured small-scale (5-15′′) extinction towards the Galactic Centre. This is the finest-scale extinction study of the Galactic Centre to date. Finally, from these VLT observationswe are able to place constraints on the stellar counterpart to the "bursting pulsar" GRO J1744-28.

Abstract:

We present the results from a large observing campaign where we obtained 61 medium resolution spectra spread over three months. We thus cover roughly five orbits and about half a precession phase. In this paper we describe the analysis of the so-called "stationary" emission lines, which we use to compute Doppler-maps of the emission distribution in the SS433-system. The radial velocities of the individual line components have been analysed. Periodic variations with the orbital period are confirmed, but also variations on longer timescales are found. These long-term variation might be either either related to the precession phase or to some transient phenomen.