The Effect of Weak Gravitational Lensing on the Angular Distribution of Gamma-Ray Bursts

If Gamma-Ray Bursts (GRBs) are cosmologically distributed standard candles and are associated with the luminous galaxies, then the observed angular distribution of all GRBs is altered due to weak gravitational lensing of bursts by density inhomogeneities. The amplitude of the effect is generally small. For example, if the current catalogs extend to $z_{max}\sim 1$ and we live in a flat $\Omega=1$ Universe, the angular auto-correlation function of GRBs will be enhanced by $\sim 8\%$ due to lensing, on all angular scales. For an extreme case of $z_{max}= 1.5$ and ($\Omega$, $\Lambda$)=(0.2, 0.8), an enhancement of $\sim 33\%$ is predicted. If the observed distribution of GRBs is used in the future to derive power spectra of mass density fluctuations on large angular scales, the effect of weak lensing should probably be taken into account.Comment: 16 pages, 2 figures, uses AASTEX macros, aasms4.sty included, accepted to Ap

Image Separation vs. Redshift of Lensed QSOs: Implications for Galaxy Mass Profiles

Recently, Park and Gott reported an interesting observation: image separation of lensed QSOs declines with QSO redshift more precipitously than expected in any realistic world model, if the lenses are taken to be either singular isothermal spheres or point masses. In this Letter I propose that the observed trend arises naturally if the lensing galaxies have logarithmic surface mass density profiles that gradually change with radius. If the observed lack of central (odd) images is also taken into account, the data favor a universal dark matter density profile over an isothermal sphere with a core. Since the trend of image separation vs. source redshift is mostly a reflection of galaxy properties, it cannot be straightforwardly used as a test of cosmological models. Furthermore, the current upper limits on the cosmological constant may have to be revised.Comment: 6 pages, including 3 figures, LaTeX. Accepted to MNRA

Bidirectional step torque filter with zero backlash characteristic Patent

Gearing system for eliminating backlash and filtering input torque fluctuations from high inertia loa

Angular correlations between LBQS and APM: Weak Lensing by the Large Scale Structure

We detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies. The QSOs are taken from the optically selected LBQS Catalogue, while the galaxies are from the APM Survey. The correlation amplitude is about a few percent on angular scales of over a degree. It is a function of QSO redshift and apparent magnitude, in a way expected from weak lensing, and inconsistent with QSO-galaxy correlations being caused by physical associations, or uneven obscuration by Galactic dust. The correlations are ascribed to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies. The amplitude of the effect found here is compared to the analytical predictions from the literature, and to the predictions of a phenomenological model, which is based on the observed counts-in-cells distribution of APM galaxies. While the latter agree reasonably well with the analytical predictions (namely those of Dolag & Bartelmann 1997, and Sanz et al. 1997), both under-predict the observed correlation amplitude on degree angular scales. We consider the possible ways to reconcile these observations with theory, and discuss the implications these observations have on some aspects of extragalactic astronomy.Comment: 9 pages; MNRAS, in pres