Effect of gravitational magnification on the measurement of distance modulus of type Ia supernovae is presented. We investigate a correlation between magnification and Hubble residual to explore how the magnification affects the estimation of cosmological parameters. We estimate magnification of type Ia supernovae in two distinct methods: one is based on convergence mass reconstruction under the weak lensing limit and the other is based on the direct measurement from galaxies distribution. Both magnification measurements are measured from Subaru Hyper Suprime-Cam survey catalogue. For both measurements, we find no significant correlation between Hubble residual and magnification. Furthermore, we correct for the apparent supernovae fluxes obtained by Supernova Legacy Survey 3-year sample using direct measurement of the magnification. We find Ω m0 = 0.287 +0.104 −0.085 and w = −1.161 +0.595 −0.358 for supernovae samples corrected for lensing magnification when we use photometric redshift catalogue of Mizuki, while Ω m0 = 0.253 +0.113 −0.087 and w = −1.078 +0.498 −0.297 for DEmP photo-z catalogue. Therefore, we conclude that the effect of magnification on the supernova cosmology is negligibly small for the current surveys; however, it has to be considered for the future supernova survey like LSST.

As a measurement of distance modulus for type Ia supernovae becomes more stringent, it is important to study various systematics for the unbiased measurement of cosmological parameters. In this paper, the effects of gravitational lensing magnification on the measurement of supernovae distance modulus and estimation of cosmological parameters are presented. Method: We use Hyper Suprime-Cam survey data to estimate the interbening large-scale structure. Two distinct methods are applied; one based on weak lensing mass reconstruction and the other based on the galaxy distribution. Then those estimations are converted to predict the possible magnification of individual supernova. Results: We find a very weak correlation between the Hubble residuals and magnification and that the Ω m and dark energy parameter w alters best fit values by O(1)% level. Conclusion: The effect of magnification can be vanishingly small given the current SNLS supernovae sample; however, it becomes important in the era of LSST and WFIRST where the number of supernovae is dramatically increase.