Browsing by Author "Raychaudhury, Somak"

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    Lens mapping algorithm for weak lensing
    (2000-09-24) Saini, Tarun Deep; Raychaudhury, Somak
    We develop an algorithm for the reconstruction of the two-dimensional mass distribution of a gravitational lens from the observable distortion of background galaxies. From the measured reduced shear γi/(1 − κ) the lens mapping is obtained, from which a mass distribution is derived. This is unlike other methods where the convergence κ is directly obtained. We show that this method works best for sub-critical lenses, but can be applied to a critical lens away from the critical lines. For finite fields the usual mass-sheet degeneracy is shown to exist in this method as well. We show that the algorithm reproduces the mass distribution within acceptable limits when applied to simulated noisy data.
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    Observing high-redshift Supernovae in lensed galaxies
    (2000-01-28) Saini, Tarun Deep; Raychaudhury, Somak; Shchekinov, Yuri A.
    Supernovae in distant galaxies that are grav- tationally lensed by foreground galaxy clusters make ex- cellent cosmological candles for measuring quantities like the density of the Universe in its various components and the Hubble constant. Distant supernovae will be more eas- ly detectable since foreground cluster lenses would mag- nify such supernovae by up to 3–4 magnitudes. We show that in the case of the lens cluster Abell 2218, the de- tectability of high-redshift supernovae is significantly en- hanced due to the lensing effects of the cluster. Since ensed supernovae will remain point images even when their host galaxies are stretched into arcs, the signal-to- noise ratio for their observation will be further enhanced, typically by an order of magnitude. We recommend moni- toring well-modelled clusters with several known arclets for the detection of cosmologically useful SNe around z = 1 and beyond.