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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…

Ultraviolet continuum variability of the quasar 3C273

Ulrich, M. H.; Courvoisier, T. J. -L.

Several quasars show an excess of radiation in the ultraviolet over the power law defined by their infrared/optical continuum. Several authors^1-4 have fitted the infrared to ultraviolet spectrum of these quasars with a combination of a power law component, line emission, blends of Fe II lines, Balmer continuum and a black-body component…

An X-ray corona in SS Cygni?

Heise, J.; King, A. R.; Watson, M. G.

A recent model¹ for the X-ray emission of non-magnetic cataclysmic variables suggests that most of the observed hard X-ray flux originates in a radiatively-cooling quasi-hydrostatic corona surrounding the white dwarf as it accretes from its companion. We present here some results from a ~7.5-h EXOSAT observation of the dwarf nova SS Cyg…

EXOSAT observations of a 2,000-s intensity dip in Seyfert galaxy NGC4151

Cruise, A. M.; Whitehouse, D. R.

Variations in the flux from active galactic nuclei (AGN) allow the testing of models of their emission mechanisms. Various suggestions for the energy generation in AGNs require the existence of a compact object, with X rays generated deep in that object's potential well and, therefore, X-ray luminosity related directly to the object responsible fo…

Evidence for an increasing 59-s period in the X-ray emission from Geminga

Caraveo, P. A.; Bignami, G. F.; Paul, J. A.

Einstein Observatory and Exosat X-ray data from 1E0630 + 178 reveal a ~50% periodic emission at >=59 s. This confirms the earlier SAS 2 and COS B findings on 2CG195 + 4 at E> 50 MeV, and provides the temporal signature for the identification of Geminga. The observations, spanning over a decade (1973-83), also suggest a very high positive per…

Exosat observation of the candidate X-ray counterpart of Geminga

Caraveo, P. A.; Bignami, G. F.; Mereghetti, S. +2 more

During a search for X-ray counterparts of the COS B>=100 MeV γ-ray sources (see refs 1, 2), observations using the Einstein Observatory revealed a new X-ray source, 1E0630 + 178, inside the ~1/2 square degree error box of the γ-ray source 2GC195+4, `Geminga'³. On the basis of its interesting properties, this source has been proposed …

X-ray astronomy: Milestone for EXOSAT

Watson, Mike

The young Sun and the atmosphere and photochemistry of the early Earth

Giampapa, M. S.; Imhoff, C. L.; Canuto, V. M. +2 more

The origin and evolution of the Earth's early atmosphere depend crucially on the dissipation time t_N of the primitive solar nebula, SN. Using different theories of turbulence, we estimate that for a 0.1 M_solar SN, t_N is 2.5-8.3Myr. Because accretion times are usually much longer, we conclude that most planetary acc…