P. Roche

Orbital, precessional and flaring variability of Cygnus X-1

We present the results of a 2.5-yr multiwavelength monitoring programme of Cygnus X-l, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular, we confirm that the 5.6-d orbital period is apparent in all wavebands, and note the existence of a wavelength dependence to the modulation, in the sense that higher energies reach minimum first. We also find a strong modulation at a period of 142 +/- 7 d, which we suggest is caused by precession and/or radiative warping of the accretion disc. Strong modulation of the hard and soft X-lay flux at this long period may not be compatible with simple models of an optically thin accretion flow and corona in the low state. We present the basic components required for more detailed future modelling of the system - including a partially optically thick jet, quasi-continuous in the low state, the base of which acts as the Comptonizing corona. In addition, we find that there are a number of flares that appear to be correlated in at least two wavebands and generally in more. We choose two of these flares to study in further detail, and find that the hard and soft X-rays are well correlated in the first, and that the soft X-rays and radio are correlated in the second. In general, the optical and infrared show similar behaviour to each other, but are not correlated with the X-rays or radio.

Solving the kilosecond quasi-periodic oscillation problem of the intermediate polar GK Persei

We detect the likely optical counterpart to previously reported X-ray QPOs in spectrophotometry of the intermediate polar GK Per during the 1996 dwarf nova outburst. The characteristic time-scales range between 4000 and 6000 s. Although the QPOs are an order of magnitude longer than those detected in the other dwarf novae we show that a new QPO model is not required to explain the long time-scale observed. We demonstrate that the observations are consistent with oscillations being the result of normal time-scale QPOs beating with the spin period of the white dwarf. We determine the spectral class of the companion to be consistent with its quiescent classification and find no significant evidence for irradiation over its inner face. We detect the white dwarf spin period in line fluxes, V/R ratios and Doppler-broadened emission profiles.

Mapping quasi-periodic oscillations from the outbursting intermediate polar GK Persei

We present time-resolved spectrophotometry of GK Per taken on the rise to outburst maximum, in which we detect 5000 s QPOs in the optical emission lines. We use this opportunity to provide a kinematically-resolved analysis of the phenomenon. Observations are consistent with reprocessing off blobs of gas orbiting within the inner accretion disc, and evidence is found for the migration of the QPO source towards the compact star over orbital timescales.

The X-ray transient XTE J2012+381

We present optical and infrared observations of the soft X-ray transient (SXT) XTE J2012+381 and identify the optical counterpart with a faint red star heavily blended with a brighter foreground star. The fainter star is coincident with the radio counterpart and appears to show weak H α emission and to have faded between observations. The RXTE All Sky Monitor light curve of XTE J2012+381 is unusual for an SXT in that after an extended linear decay, it settled into a plateau state for about 40 days before undergoing a weak mini-outburst. We discuss the nature of the object and suggest similarities to long orbital period SXTs.