The distant galaxy cluster XLSSJ022403.9-041328 on the L X –T X –M scaling relations using Chandra and XMM–Newton observations

We present a very detailed analysis of Chandra and XMM–Newton observations of XLSSJ022403.9-041328 galaxy cluster of z=1, which was detected during the XMM-Newton Large Scale Structure survey. To define the “luminosity-temperature-mass”, L _X –T _X –M, scaling relations we built temperature, surface brightness, density, and mass profiles. The total gravitational mass of this cluster was taken within the scaled radius, R ₅₀₀, was determined under the assumption of hydrostatic equilibrium for intercluster gas and spherical symmetry of a cluster. The temperature of XLSSJ022403.9-041328 was found to be 4.5±0.7 keV from the Chandra data, and 3.8±0.3 from the XMM–Newton data. The total gravitational mass is equal to 1.44±0.23×10¹⁴ M _⊙ at the corresponding radius, while the fraction of gas is equal to 15 % of a total mass. These values were used to define the XLSSJ022403.9-041328 galaxy cluster at the L _X –T _X –M _g scaling relations, and for all of these cases we got agreement which fitting well with self-similar model. This research permits us to use L _X –T _X –M relations for galaxy clusters at a highest redshift in the cosmological probes.     

The unusual X-ray light curve of GRB 080307: the onset of the afterglow?

Swift -detected GRB 080307 showed an unusual smooth rise in its X-ray light curve around 100 s after the burst, at the start of which the emission briefly softened. This 'hump' has a longer duration than is normal for a flare at early times and does not demonstrate a typical flare profile. Using a two-component power-law-to-exponential model, the rising emission can be modelled as the onset of the afterglow, something which is very rarely seen in Swift -X-ray light curves. We cannot, however, rule out that the hump is a particularly slow early-time flare, or that it is caused by upscattered reverse shock electrons.     

The effect of mass-loss and semiconvection on the evolution of a 15M ⊙ population I star

Evolutionary sequences are computed from the main sequence to central helium exhaustion for a 15M star, with an initial composition ofX=0.70,Y=0.27,Z=0.03. Parallel sequences are computed to investigate the effects of different mass loss rates on the evolution of the star. These rates are chosen to reflect the physical causes of the mass loss, and occur at all phases of evolution. One sequence without, and one with, mass loss are recomputed, allowing for semiconvection and full convection in intermediate mass zones, using the Schwarzschild and Härm criterion for convective neutrality.Low to moderate rates of mass loss in the early evolutionary phases shift the evolution to lower luminosities and effective temperatures, but do not radically alter the form of evolution. However, the resulting evolutionary sequences can be up to 25% undermassive for their luminosity as they enter the red giant branch (RGB). Most sequences evolve through a subsequent stable blue phase (the blue loop), which is shifted to lower luminosities and effective temperatures by the previous mass loss and is also widened. This blue loop is suppressed if approximately 10% of the stellar mass is lost in the RGB. Mass loss delays the evolution of the central region of the star relative to that of the outer region, so that central helium ignition and exhaustion are displaced to later points on the evolutionary tracks. Mass loss also reduces the size of the helium core, although its mass fraction is larger.If semiconvective and intermediate fully convective zones are included, then in a sequence without mass loss these zones greatly alter the chemical profile of the model. The sequence evolves at a higher luminosity, with a stable blue supergiant phase occurring prior to the RGB. Central helium exhaustion occurs during the ascent of the RGB. However, if mass loss is included, the extent of these zones is drastically reduced, and the evolutionary pattern is similar to that without such zones. No blue loop is found.Observations indicate that the blue supergiant region is wider and bluer than predicted by previous evolutionary calculations. The present results show that mass loss widens and reddens this phase. Hence, the inclusion of other factors will be necessary to reconcile theory and observations.     

The X-ray spectrum of the bright galactic bulge source X1813−14=GX17+2

The spectral analysis of the persistent X-ray flux from the bright galactic bulge X-ray source and an X-ray burster X1813–14=GX17+2 is presented. A model with a single thermal bremsstrahlung continuum plus iron emission line at 6.7 keV fits the lower and higher intensity state data reasonably well. The line feature observed here is reproduced by a single emission line at 6.7 keV with intrinsic line width less than 0.7 keV. The equivalent width of the line ranges between 52 and 43 eV, depending on the intensity state of the source. This implies that the observed line is mostly due to helium-like iron (Fexxv). The properties of the line suggest that line-emitting matter is located far outside the neutron star.     

The dependence of galaxy formation on cosmological parameters: can we distinguish between the WMAP1 and WMAP3 parameter sets?

We combine N -body simulations of structure growth with physical modelling of galaxy evolution to investigate whether the shift in cosmological parameters between the first- and third-year results from the Wilkinson Microwave Anisotropy Probe ( WMAP ) affects predictions for the galaxy population. Structure formation is significantly delayed in the WMAP3 cosmology, because the initial matter fluctuation amplitude is lower on the relevant scales. The decrease in dark matter clustering strength is, however, almost entirely offset by an increase in halo bias, so predictions for galaxy clustering are barely altered. In both cosmologies, several combinations of physical parameters can reproduce observed, low-redshift galaxy properties; the star formation, supernova feedback and active galactic nucleus feedback efficiencies can be played off against each other to give similar results. Models which fit observed luminosity functions predict projected two-point correlation functions which scatter by about 10–20 per cent on large scale and by larger factors on small scale, depending both on cosmology and on details of galaxy formation. Measurements of the pairwise velocity distribution prefer the WMAP1 cosmology, but careful treatment of the systematics is needed. Given present modelling uncertainties, it is not easy to distinguish between the WMAP1 and WMAP3 cosmologies on the basis of low-redshift galaxy properties. Model predictions diverge more dramatically at high redshift. Better observational data at   z > 2  will better constrain galaxy formation and perhaps also cosmological parameters.