Corrections for Gravitational Lensing of Supernovae: Better than Average?

We investigate the possibility of correcting for magnification due to gravitational lensing of standard candle sources, such as Type Ia supernovae. Our method uses the observed properties of the foreground galaxies along the lines of sight to each source, and the accuracy of the lensing correction depends on the quality and depth of these observations as well as the uncertainties in translating the observed luminosities to the matter distribution in the lensing galaxies. The current work is limited to cases in which the matter density is dominated by the individual galaxy halos. However, it is straightforward to generalize the method to also include gravitational lensing from cluster scale halos. We show that the dispersion due to lensing for a standard candle source at z = 1.5 can be reduced from about 7% to <img src="http://ej.iop.org/icons/Entities/lesssim.gif" />3%; i.e., the magnification correction is useful in reducing the scatter in the Type Ia Hubble diagram, especially at high redshifts where the required long exposure times make it hard to reach large statistics and the dispersion due to lensing becomes comparable to the intrinsic Type Ia scatter.