Search Publications

A helium-burning white dwarf binary as a supersoft X-ray source

Burgess, J. M.; Werner, K.; Haberl, F. +12 more

Type Ia supernovae are cosmic distance indicators^1,2, and the main source of iron in the Universe^3,4, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed⁵ and suggested as Type I…

Localized thermonuclear bursts from accreting magnetic white dwarfs

Knigge, C.; de Martino, D.; Done, C. +16 more

Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs^1-3. It has been predicted^4-6 that localized thermonuclear bursts on white dwarfs can also take place, similar to type-I X-ray bursts observed in accreting neutron stars. Unexplained rapid bursts from the binar…

Low-frequency divergent X-ray variability in the Seyfert galaxy NGC4051

Elvis, M.; Watson, M. G.; Lawrence, A. +1 more

The X-ray emission from NGC4051, a nearby low luminosity Type 1 Seyfert galaxy, exhibits variations that are both rapid and apparently quasi-periodic^1,2. Many Seyfert galaxies are variable³ but our knowledge of the form of variability has not advanced substantially since early well-resolved observations⁴ and attemp…

Fractal X-ray time variability and spectral invariance of the Seyfert galaxy NGC5506

McHardy, Ian; Czerny, Bozena

Rapid X-ray variability has long been sought after in active galactic nuclei (AGN) as an indicator of such parameters as the mass-to-energy conversion efficiency and black hole mass. Although some interesting variability information has been gained from early observations (for example see ref. 1 for a review) the faintness of AGN, combined with th…

Observations of active galaxies

Mushotzky, Richard

New information obtained by the EXOSAT satellite on the nature of the X-ray variability in AGNs is discussed. From the EXOSAT data, it is seen that many more AGNs vary on short timescales; in some cases, the character of the time variability is quantitatively and qualitatively different than expected from the flare model of the variability. Data o…

Coordinated Exosat and spectroscopic observations of flare stars and coronal heating

Foing, B. H.; Rodono, M.; Butler, C. J. +1 more

The X-ray flux of dMe stars is thought to arise from two distinct mechanisms, one involving a continuous `quiescent' emission from a high-temperature plasma and the other involving the dramatic flare events which have long been known to occur on these stars. We present here some results of simultaneous monitoring of the two flare stars, UV Ceti an…

New results from Exosat

Fabian, A. C.

The galactic ridge observed by Exosat

Warwick, R. S.; Watson, M. G.; Turner, M. J. L. +1 more

We have used Exosat to map the distribution of X-ray emission in the galactic plane. In addition to numerous point sources, the map reveals a narrow continuous ridge of emission which extends along the galactic plane either side of the galactic centre out to ~40° longitude. The origin of this feature remains uncertain although a major contribution…

An extended X-ray low state from Hercules X-1

Pietsch, W.; Parmar, A. N.; White, N. E. +4 more

Hercules X-1 exhibits a 35-day cycle in its X-ray intensity^1,2 in addition to its pulsar rotational and orbital periodicities of 1.24 s and 1.7 days respectively. The effects of X-ray heating on the companion are visible throughout the 35-day cycle³, suggesting that the observed intensity modulation is caused by periodic bloc…

Transient quasi-periodic oscillations in in the X-ray flux of Cygnus X-3

van der Klis, M.; Jansen, F. A.

Cygnus X-3, a bright X-ray source at a distance¹ of more than ~12 kpc beyond the edge of the galactic plane, has peculiar properties including very strong radio outbursts², possibly showing jet-like features³, and emission in various γ-ray bands^4-6 (but see ref. 7). The discovery of its 4.8-h X-ray perio…