This paper exploits the gravitational magnification of SNe Ia to measure properties of dark matter haloes .
Gravitationally magnified and de-magnified SNe Ia should be brighter and fainter than average , respectively .
The magnification of individual SNe Ia can be computed using observed properties of foreground galaxies and dark matter halo models .
We model the dark matter haloes of the galaxies as truncated singular isothermal spheres with velocity dispersion and truncation radius obeying luminosity dependent scaling laws .

A homogeneously selected sample of 175 SNe Ia from the first 3-years of the Supernova Legacy Survey ( SNLS ) in the redshift range 0.2 \la z \la 1 is used to constrain models of the dark matter haloes associated with foreground galaxies .
The best-fitting velocity dispersion scaling law agrees well with galaxy–galaxy lensing measurements .
We further find that the normalisation of the velocity dispersion of passive and star forming galaxies are consistent with empirical Faber–Jackson and Tully–Fisher relations , respectively .
If we make no assumption on the normalisation of these relations , we find that the data prefer gravitational lensing at the 92 per cent confidence level .
Using recent models of dust extinction we deduce that the impact of this effect on our results is very small .

We also investigate the brightness scatter of SNe Ia due to gravitational lensing , which has implications for SN Ia cosmology .
The gravitational lensing scatter is approximately proportional to the SNÂ Ia redshift .
We find the constant of proportionality to be B \simeq 0.055 _ { -0.041 } ^ { +0.039 } mag ( B \la 0.12 mag at the 95 per cent confidence level ) .
If this model is correct , the contribution from lensing to the intrinsic brightness scatter of SNe Ia is small for the SNLS sample .
According to the best-fitting dark matter model , gravitational lensing should , however , contribute significantly to the brightness scatter at z \ga 1.6 .