A Huge Drop in X-ray Luminosity of the Non-Active Galaxy RXJ1242.6-1119A, and First Post-Flare Spectrum - Testing the Tidal Disruption Scenario

It has been suggested that an unavoidable consequence of the existence of supermassive black holes, and the best diagnostic of their presence in non-active galaxies, would be occasional tidal disruption of stars captured by the black holes. These events manifest themselves in form of luminous flares powered by accretion of debris from the disrupted star into the black hole. Candidate events among optically non-active galaxies emerged in the past few years. For the first time, we have looked with high spatial and spectral resolution at one of these most extreme variability events ever recorded among galaxies. Here, we report measuring a factor ~200 drop in luminosity of the X-ray source RXJ 1242-1119 with the X-ray observatories Chandra and XMM-Newton, and perform key tests of the favored outburst scenario, tidal disruption of a star by a supermassive black hole. We show that the detected `low-state' emission has properties such that it must still be related to the flare. The power-law shaped post-flare X-ray spectrum indicates a `hardening' compared to outburst. The inferred black hole mass, the amount of liberated energy, and the duration of the event favor an accretion event of the form expected from the (partial or complete) tidal disruption of a star (abstract abbreviated).Comment: to appear in March 1 issue of ApJ Letters (submitted Nov. 10, accepted in Dec. 2003); background information available at http://www.xray.mpe.mpg.de/~skomossa

Oscillations of MHD shock waves on the surfaces of T Tauri stars

This work treats the matter deceleration in a magnetohydrodynamics radiative shock wave at the surface of a star. The problem is relevant to classical T Tauri stars where infalling matter is channeled along the star's magnetic field and stopped in the dense layers of photosphere. A significant new aspect of the present work is that the magnetic field has an arbitrary angle with respect to the normal to the star's surface. We consider the limit where the magnetic field at the surface of the star is not very strong in the sense that the inflow is super Alfv\'enic. In this limit the initial deceleration and heating of plasma (at the entrance to the cooling zone) occurs in a fast magnetohydrodynamic shock wave. To calculate the intensity of radiative losses we use "real" and "power-law" radiative functions. We determine the stability/instability of the radiative shock wave as a function of parameters of the incoming flow: velocity, strength of the magnetic field, and its inclination to the surface of the star. In a number of simulation runs with the "real" radiative function, we find a simple criterion for stability of the radiative shock wave. For a wide range of parameters, the periods of oscillation of the shock wave are of the order 0.02-0.2 sec.Comment: 13 pages, 11 figures, submitted to the MNRAS after revision, see animations at http://www.astro.cornell.edu/us-rus/shock.ht

Lack of long-term acclimation in Antarctic encrusting species suggests vulnerability to warming

Marine encrusting communities play vital roles in benthic ecosystems and have major economic implications with regards to biofouling. However, their ability to persist under projected warming scenarios remains poorly understood and is difficult to study under realistic conditions. Here, using heated settlement panel technologies, we show that after 18 months Antarctic encrusting communities do not acclimate to either +1 °C or +2 °C above ambient temperatures. There is significant up-regulation of the cellular stress response in warmed animals, their upper lethal temperatures decline with increasing ambient temperature and population genetic analyses show little evidence of differential survival of genotypes with treatment. By contrast, biofilm bacterial communities show no significant differences in community structure with temperature. Thus, metazoan and bacterial responses differ dramatically, suggesting that ecosystem responses to future climate change are likely to be far more complex than previously anticipated

The IIASA/LUC Project Georeferenced Database for the former U.S.S.R. Volume 6: Agricultural Regionalization.

The IIASA/LUC georeferenced database for the former U.S.S.R. was created within the framework of the project "Modeling Land Use and Land Cover Changes in Europe and Northern Asia" (LUC). For Russia, essential information on relief, soil, vegetation, land cover and use, etc., for routine environmental analysis was lacking when the LUC project started developing the database. In addition, the environmental data on the former U.S.S.R. which was available occurred in formats (papers, tables, etc.) that in general could not be used with modern information technology, and in particular in model building. In creating the LUC project database, we have established a threefold task: (1) to obtain the relevant information for the LUC project modeling exercises; (2) to develop data which is applicable to modern information technology; (3) to contribute a series of digital databases which could be applied for a number of other specific analyses by the national and international scientific community. In defining the tasks it was agreed to create a set of digital databases which could be handled by geographic information systems (GIS). The full set of georeferenced digital databases was combined into the LUC project's GIS, using ARC/INFO. However, each individual item (physiography, soil, vegetation, etc.) was created as a unique specific digital database, allowing each item to be used separately, depending on users' needs. The complete series of the unique georeferenced digital databases for the territory of the former U.S.S.R. is described in the IIASA/LUC volumes: Volume 1 -- Physiography (landforms, slope conditions, elevations); Volume 2 -- Soil; Volume 3 -- Soil degradation status (Russia); Volume 4 -- Vegetation; Volume 5 -- Land categories; Volume 6 -- Agricultural regionalization