Cosmic equation of state and advanced LIGO-type gravitational wave experiments

It is hoped that the future generation of interferometric gravitational wave detectors will provide accurate measurements of the final stages of binary in-spirals. The sources probed by such experiments are of extragalactic origin and the observed chirp mass is the intrinsic chirp mass multiplied by (1+ z ) where z is the redshift of the source. Moreover the luminosity distance is a direct observable in such experiments. This creates the possibility to establish a new kind of cosmological test, supplementary to more standard ones.
Recent observations of distant type Ia supernovae light curves suggest that the expansion of the Universe has recently begun to accelerate. A popular explanation of the present accelerating expansion of the Universe is to assume that some part Ω_Q of the matter–energy density is in the form of a dark component called 'the quintessence' with the equation of state p _Q= wρ _Q with w ≥−1 . In this paper we consider the predictions concerning observations of binary in-spirals in future LIGO-type interferometric experiments assuming a 'quintessence cosmology'. In particular we compute the expected redshift distributions of observed events in the a priori admissible range of parameters describing the equation of state for the quintessence. We find that this distribution has a robust dependence on the cosmic equation of state.     

Chandra observations of the galaxy cluster Abell 1835

We present the analysis of 30 ks of Chandra observations of the galaxy cluster Abell 1835. Overall, the X-ray image shows a relaxed morphology, although we detect substructure in the inner 30-kpc radius. Spectral analysis shows a steep drop in the X-ray gas temperature from ∼12 keV in the outer regions of the cluster to ∼4 keV in the core. The Chandra data provide tight constraints on the gravitational potential of the cluster which can be parametrized by a Navarro, Frenk & White model. The X-ray data allow us to measure the X-ray gas mass fraction as a function of radius, leading to a determination of the cosmic matter density of
   
. The projected mass within a radius of ∼150 kpc implied by the presence of gravitationally lensed arcs in the cluster is in good agreement with the mass models preferred by the Chandra data. We find a radiative cooling time of the X-ray gas in the centre of Abell 1835 of about
   
. Cooling-flow model fits to the Chandra spectrum and a deprojection analysis of the Chandra image both indicate the presence of a young cooling flow (∼     with an integrated mass deposition rate of     within a radius of 30 kpc. We discuss the implications of our results in the light of recent Reflection Grating Spectrograph (RGS) observations of Abell 1835 with XMM-Newton .     

Can Jupiters be found by monitoring Galactic bulge microlensing events from northern sites?

In 1998 the EXPORT team monitored microlensing event light curves using a charge-coupled device (CCD) camera on the IAC 0.8-m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic bulge sources make a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1-m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass.