The multi-temperature X-ray spectrum of the intermediate polar V1223 Sagittarii

We describe fits to the Ginga LAC and ASCA GIS and SIS X-ray spectra of the intermediate polar V1223 Sgr using a multi-temperature emission model and including reflection from the white dwarf surface. Shock temperatures of and were obtained for the Ginga LAC, ASCA GIS and SIS instruments, respectively, giving a mean value of The data reveal significant amounts of reflection as well as a heavy metal underabundance by a factor of 2.
Multiple absorption components are required to successfully model the observed X-ray spectra at low energies, suggesting the presence of complex intrinsic absorption. All data sets reveal a low-energy spectral hardening at the minimum in the spin cycle caused by an increase in the amount of absorption at this phase. The requirement of such complex absorption is becoming increasingly common in the good quality X-ray spectra from magnetic cataclysmic variables.     

Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities

Experimental Astronomy - The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky. It will specifically exploit large samples of gamma-ray bursts to probe the...     

X-ray observations of cataclysmic variables

The X-ray observatory EXOSAT spent over 1000 hours observing cataclysmic variables. Some of the major results reviewed here are: soft X-ray light curve changes in AM Her objects, orbital effects in the X-ray light curves of intermediate polars and U Gem, regular behaviour in the inter-outburst X-ray flux of VW Hyi, and X-ray emission from the tenuous remnant of the recent recurrent nova RS Oph. The ability of EXOSAT to make long uninterupted observations at high sensitivity over a broad spectral range and to react quickly to cosmic events has yielded a dataset of a quality that will not be surpassed for many years.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

The changing X-ray light curves of the intermediate polar FO Aquarii

Comparison of five X-ray observations of the intermediate polar FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. In particular, power spectra of the 1988 Ginga   and 1993 ASCA   data reveal strong sideband and orbital variations, whereas the 1990 Ginga   observation does not. This suggests that the amount of stream-fed accretion varies with epoch, and the system was accreting predominantly from a disc in 1990.   In contrast to other intermediate polars, the X-ray spin-pulse profiles show significant variations between observations, ranging from relatively sinusoidal to sawtooth-shaped at medium energies. During the 1988 and 1990 observations a notch is visible at spin phase zero, due to the presence of an interpulse at phase 0.85, which is absent during the other observations. At lower energies a narrow pulse of emission is seen at spin phase 0.2.   We interpret the pulse profile from the 1990 Ginga   observation using a model for accretion from a disc on to a dipolar magnetic field, the axis of which is offset from the white dwarf centre by ∼ 0.15 white dwarf radii. In order to account for the later occurrence of the hardness-ratio maximum in 1988 and 1993, we suggest that the accretion-rate profile changes so that accretion is favoured along the field lines which trail the magnetic pole. This also accounts for the disappearance of the interpulse and notch in 1993.     

The Late Devensian-Flandrian transition depicted by serial insect faunas from West Bromwich, Staffordshire, England

A bed of peat resting on sands and gravels and reaching the present-day ground surface, was investigated for beetles, and seven radiocarbon dates were obtained. The beetles indicated that the lowest layers of the peat, dated around 12,000 B.P., were laid down in boggy conditions in a treeless landscape under a climatic regime which was rather cooler than present day. Two quite sudden changes in the aspect of the fauna then followed. The first was the incoming of an assemblage indicative of a climate of arctic severity. This layer was not dated but if the rate of deposition was constant during this period it must have been around 11,000 B. P. The second change was the equally rapid disappearance of this northern fauna about 1000 years later. Succeeding layers then contained beetles suggesting conditions as warm as those of the present day, with species indicating both coniferous and deciduous trees appearing before 9500 B.P.