Was Supernova 1997ff at z ∼ 1.7 magnified by gravitational lensing?

The quest for the cosmological parameters has come to fruition with the identification of a number of supernovae at a redshift of z similar to 1. Analyses of the brightness of these standard candles reveal that the Universe is dominated by a large cosmological constant. The recent identification of the z similar to 1.7 SN 1997ff in the northern Hubble Deep Field has provided further evidence for this cosmology. Here we examine the case for gravitational lensing of SN 1997ff owing to the presence of galaxies lying along our line of sight. We find that, while the alignment of SN 1997ff with foreground masses is not favourable for it to be multiply imaged and strongly magnified, two galaxies do lie close enough to result in significant magnification: mu similar to 1.4 for the case where these elliptical galaxies have a velocity dispersion of 200 kms(-1). Given the small difference between supernova brightnesses in different cosmologies, detailed modelling of the gravitational lensing properties of the intervening matter is therefore required before the true cosmological significance of SN 1997ff can be deduced.