Was SN1997ff at z~1.7 magnified by gravitational lensing?

Abstract

The quest for the cosmological parameters has come to fruition with the identification of a number of supernovae at a redshift of $z\sim1$. Analyses of the brightness of these standard candles reveal that the Universe is dominated by a large cosmological constant. The recent identification of the $z\sim1.7$ SN1997ff in the northern Hubble Deep Field has provided further evidence for this cosmology. Here we examine the case for gravitational lensing of SN1997ff due to the presence of galaxies lying along our line of sight. We find that, while the alignment of SN1997ff with foreground masses was not favorable for it to be multiply imaged and strongly magnified, two galaxies did lie close enough to result in significant magnification: $μ\sim1.4$ for the case where these elliptical galaxies have velocity dispersion $200 {\rm km/s}$. Given the small difference between supernova brightnesses in different cosmologies, detailed modeling of the gravitational lensing properties of the intervening matter is therefore required before the true cosmological significance of SN1997ff can be deduced.