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We report on the variability of the iron K emission line in the Seyfert 1 galaxy MCG-6-30-15 during a four-day ASCA observation. The line consists of a narrow core at an energy of about 6.4 keV, and a broad red wing extending to below 5 keV, which are interpreted as line emission arising from the inner parts of an accretion disk. The narrow core correlates well with the continuum flux whereas the broad wing weakly anti-correlates. When the source is brightest, the line is dominated by the narrow core, whilst during a deep minimum, the narrow core is very weak and a huge red tail appears. However, at other times when the continuum shows rather rapid changes, the broad wing is more variable than the narrow core, and shows evidence for correlated changes contrary to its long time scale behaviour. The peculiar line profile during the deep minimum spectrum suggests that the line emitting region is very close to a central spinning (Kerr) black hole where enormous gravitational effects operate.

We present precise measurements of the X‐ray gas mass fraction for a sample of luminous, relatively relaxed clusters of galaxies observed with the Chandra observatory, for which independent confirmation of the mass results is available from gravitational lensing studies. Parametrizing the total (luminous plus dark matter) mass profiles using the model of Navarro, Frenk & White, we show that the X‐ray gas mass fractions in the clusters asymptote towards an approximately constant value at a radius r2500, where the mean interior density is 2500 times the critical density of the Universe at the redshifts of the clusters. Combining the Chandra results on the X‐ray gas mass fraction and its apparent redshift dependence with recent measurements of the mean baryonic matter density in the Universe and the Hubble constant determined from the Hubble Key Project, we obtain a tight constraint on the mean total matter density of the Universe, , and measure a positive cosmological constant, . Our results are in good agreement with recent, independent findings based on analyses of anisotropies in the cosmic microwave background radiation, the properties of distant supernovae, and the large‐scale distribution of galaxies.

We present a critical analysis of the usual interpretation of the multicolour disc model parameters for black hole candidates in terms of the inner radius and temperature of the accretion disc. Using a self‐consistent model for the radiative transfer and the vertical temperature structure in a Shakura–Sunyaev disc, we simulate the observed disc spectra, taking into account Doppler blurring and gravitational redshift, and fit them with multicolour models. We show not only that such a model systematically underestimates the value of the inner‐disc radius, but that when the accretion rate and/or the energy dissipated in the corona are allowed to change, the inner edge of the disc, as inferred from the multicolour model, appears to move even when it is in fact fixed at the innermost stable orbit.

Conduction may play an important role in reducing cooling flows in galaxy clusters. We analyse a sample of sixteen objects using Chandra data and find that a balance between conduction and cooling can exist in the hotter clusters (T > 5 keV), provided the plasma conductivity is close to the unhindered Spitzer value. In the absence of any additional heat sources, a reduced mass inflow must develop in the cooler objects in the sample. We fit cooling flow models to deprojected data and compare the spectral mass deposition rates found to the values required to account for the excess luminosity, assuming Spitzer-rate heat transfer over the observed temperature gradients. The mass inflow rates found are lower than is necessary to maintain energy balance in at least five clusters. However, emission from cooling gas may be partially absorbed. We also compute the flux supplied by turbulent heat transport (Cho et al. 2003) and find conductivity profiles which follow a strikingly similar temperature dependence to the conductivity values required to prevent cooling. Finally, we show that the cluster radio luminosities vary by over five orders of magnitude in objects with X-ray luminosities differing by no more than a factor of a few. This suggests that there is unlikely to be a straightforward correlation between the mechanical power provided by the radio lobes and the rate of energy loss in cooling flow clusters.Comment: Submitted to MNRA

We examine the effects of cooling flows on the TX–LBol relation for a sample of the most X‐ray luminous (LBol > 1045 erg s−1) clusters of galaxies known. Using high‐quality ASCA X‐ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X‐ray properties of the clusters and show that this reduces the previously noted dispersion in the TX–LBol relationship. More importantly, the slope of the relationship is flattened from LBol ∝ T3X to approximately LBol ∝ T2X, in agreement with recent theoretical models which include the effects of shocks and pre‐heating on the X‐ray gas. We find no evidence for evolution in the TX–LBol relation within z ∼ 0.3. Our results demonstrate that the effects of cooling flows must be accounted for before cosmological parameters can be determined from X‐ray observations of clusters. The results presented here should provide a reliable basis for modelling the TX–LBol relation at high X‐ray luminosities.

A B S T R A C TWe present a detailed and homogeneous analysis of the ROSAT PSPC surface brightness pro®les of 36 clusters of galaxies with high X-ray luminosity (L X * 10 45 erg s À1 ) and redshifts between 0.05 and 0.44. Using recent ASCA estimates of the temperature of the gas for most of the clusters in the sample, we apply both the deprojection technique and model ®tting to the surface brightness pro®les to constrain the gas and dark matter distributions under the assumption that the gas is both isothermal and hydrostatic.Applying robust estimators, we ®nd that the gas fraction within r 500 of the clusters in our sample has a distribution centred on f gas r 500 0:168 h À1:5 50 . The gas fraction ranges from 0.101 to 0.245 at the 95 per cent con®dence level. The values of f gas show highly signi®cant variations between individual clusters, which may be explained if the dark matter has a signi®cant baryonic component. Within a cluster, the average radial dependence of the gas mass fraction increases outward as r s , with s , 0:20. Combining these results with those of primordial nucleosynthesis calculations and the current estimate of H 0 , the above central location implies Q 0;m & 0:56 at the 95 per cent con®dence level. This upper limit decreases to 0.34 if we take the highest signi®cant estimates for f gas .A signi®cant decrease in cluster gas fraction with redshift from the local value, f gas;0 , of 0.21, found assuming Q 0;m 1, is also reduced if Q 0;m is low.