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

The quest for the cosmological parameters has come to fruition with the ide ntification of a number of supernovae at a redshift of z similar to 1. Anal yses of the brightness of these standard candles reveal that the Universe i s 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 provid ed further evidence for this cosmology. Here we examine the case for gravit ational 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 fore ground masses is not favourable for it to be multiply imaged and strongly m agnified, two galaxies do lie close enough to result in significant magnifi cation: 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 s upernova brightnesses in different cosmologies, detailed modelling of the g ravitational lensing properties of the intervening matter is therefore requ ired before the true cosmological significance of SN 1997ff can be deduced.