Pulsars, transients and relativistic astrophysics

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.

Abstract:

A long-standing question is whether active galactic nuclei (AGN) vary like Galactic black hole systems when appropriately scaled up by mass. If so, we can then determine how AGN should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. As X-ray emission is produced very close to the black holes, it provides one of the best diagnostics of their behaviour. A characteristic timescale--which potentially could tell us about the mass of the black hole--is found in the X-ray variations from both AGN and Galactic black holes, but whether it is physically meaningful to compare the two has been questioned. Here we report that, after correcting for variations in the accretion rate, the timescales can be physically linked, revealing that the accretion process is exactly the same for small and large black holes. Strong support for this linkage comes, perhaps surprisingly, from the permitted optical emission lines in AGN whose widths (in both broad-line AGN and narrow-emission-line Seyfert 1 galaxies) correlate strongly with the characteristic X-ray timescale, exactly as expected from the AGN black hole masses and accretion rates. So AGN really are just scaled-up Galactic black holes.