A fundamental plane of black hole activity

We examine the disc--jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the X-ray and radio bands. We compile a sample of ~100 active galactic nuclei with measured mass, 5 GHz core emission, and 2-10 keV luminosity, together with 8 galactic black holes with a total of ~50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_{R}) and the X-ray (L_{X}) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with {\em both} M and L_{X}, at a highly significant level. In particular, we show that the sources define a ``fundamental plane'' in the three-dimensional (log L_{R},log L_{X},log M) space, given by log L_{R}=(0.60^{+0.11}_{-0.11}) log L_{X} +(0.78^{+0.11}_{-0.09}) log M + 7.33^{+4.05}_{-4.07}, with a substantial scatter of \sigma_{R}=0.88. We compare our results to the theoretical relations between radio flux, black hole mass, and accretion rate derived by Heinz and Sunyaev (2003). Such relations depend only on the assumed accretion model and on the observed radio spectral index. Therefore, we are able to show that the X-ray emission from black holes accreting at less than a few per cent of the Eddington rate is unlikely to be produced by radiatively efficient accretion, and is marginally consistent with optically thin synchrotron emission from the jet. On the other hand, models for radiatively inefficient accretion flows seem to agree well with the data.Comment: 21 pages, 8 figures (2 in colour). Revised version accepted for publication by MNRAS. Improved and extended discussio

An optically thick inner corona geometry for the Very High State Galactic Black Hole XTE J1550-564

(truncated version) The X-ray spectra of Galactic binary systems in the very high state show both strong disk emission and a strong, steep tail to high energies. We use simultaneous optical-ASCA-RXTE data from the black hole transient XTE J1550-564 as a specific example, and show that these have disc spectra which are significantly lower in temperature than those seen from the same source at the same luminosity when in the disc dominated state. If these give a true picture of the disc then either the disc emissivity has reduced, and/or the disc truncates above the last stable orbit. However, it is often assumed that the tail is produced by Compton scattering, in which case its shape in these spectra requires that the Comptonising region is marginally optically thick (tau~2-3), and covers a large fraction of the inner disc. This will distort our view of the disc. We build a theoretical model of a Comptonising corona over an inner disc, and fit this to the data, but find that it still requires a large increase in inner disc radius for a standard disc emissivity. Instead it seems more probable that the disc emissivity changes in the presence of the corona. We implement the specific inner disc-corona coupling model of Svensson & Zdziarski (1994) and show that this can explain the low temperature/high luminosity disc emission seen in the very high state with only a small increase in radius of the disc. While this inferred disc truncation is probably not significant given the model uncertainties, it is consistent with the low frequency QPO and gives continuity of properties with the low/hard state spectra.Comment: MNRAS accepted version, with major expansion of the discussion to include comments on comptonisation, extreme broad iron lines and high frequency QPO's. 18 pages, 8 figure

11 1 Technical Cooperation Officer, Overseas Development Administration

Eight two-litre glass jars were used as anaerobic digesters in a trial to compare biogas production from mixtures of cattle slurry and pressed sugar-cane stalk. It was found that as the percentage of pressed cane stalk (PCS) was increased, the initial pH of the mixture decreased and initial gas production was impaired. The PCS was degraded much more slowly than the cattle slurry, although total production was not reduced significantly by the presence of up to 56.7% PCS (dry-matter basis) in the fermentation mixture. Gas production was seriously reduced when the level of PCS rose to 80%. Initial pH of this mixture was 4.6 and 4.4 for the treatments with and without urea respectively. The addition of urea had the effect of increasing pH, and substantially reducing the length of the lag phase of the cumulative biogas production curves

Reprocessing of X-rays in AGN. I. Plane parallel geometry -- test of pressure equilibrium

We present a model of the vertical stratification and the spectra of an irradiated medium under the assumption of constant pressure. Such a solution has properties intermediate between constant density models and hydrostatic equilibrium models, and it may represent a flattened configuration of gas clumps accreting onto the central black hole. Such a medium develops a hot skin, thicker than hydrostatic models, but thinner than constant density models, under comparable irradiation. The range of theoretical values of the alpha_ox index is comparable to those from hydrostatic models and both are close to the observed values for Seyfert galaxies but lower than in quasars. The amount of X-ray Compton reflection is consistent with the observed range. The characteristic property of the model is a frequently multicomponent iron K alpha line.Comment: accepted for publication in Astronomy and Astrophysic

A burst from the direction of UZ Fornacis with XMM-Newton

The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ksec exposure with the EPIC cameras, suggesting that the accretion rate either decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ For during the observation. Spectral fits favour optically thin, kT = 4.4 keV thermal emission. Detection of the burst by the on-board Optical Monitor indicates that this was most probably an accretion event. The 0.1-10 keV luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from high state polars and would result from the potential energy release of ~ 10^16 g of gas. There is no significant soft excess due to reprocessing in the white dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres

The broad-band X-ray spectrum of the dipping Low Mass X-ray Binary EXO0748--676

We present results of a 0.1-100 keV BeppoSAX observation of the dipping LMXRB EXO 0748-676 performed in 2000 November. During the observation the source exhibited X-ray eclipses, type I X-ray bursts and dipping activity over a wide range of orbital phases. The 0.1-100keV "dip-free"(ie. dipping and eclipsing intervals excluded) spectrum is complex,especially at low-energies where a soft excess is present. Two very different spectral models give satisfactory fits. The first is the progressive covering model, consisting of separately absorbed black body and cut-off power-law components.The second model is an absorbed cut-off power-law together with a moderately ionized absorber with a sub-solar abundance of Fe and a 2.13 keV absorption feature (tentatively identified with Si xiii). This ionized absorber may be the same feature as seen by Chandra during dips from EXO 0748-676.Comment: 7 pages, 5 figures, paper accepted for publication in Astronomy and Astrophysic