Cosmological Implications of the Highest Redshift Supernova (Known)

I will present photometric observations of an apparent Type Ia supernova (SN Ia) at a redshift of ~1.7, the farthest SN observed to date. SN 1997ff, was discovered in a repeat observation by the HST of the HDF, and serendipitously monitored with NICMOS on HST throughout the GTO campaign. Fits to observations of the SN provide constraints for the redshift-distance relation of SNe~Ia and a powerful test of the current accelerating Universe hypothesis. The apparent SN brightness is consistent with that expected in the decelerating phase of the preferred cosmological model, Omega_M~1/3, Omega_Lambda~2/3. It is inconsistent with grey dust or simple luminosity evolution, candidate astro-physical effects which could mimic past evidence for an accelerating Universe from SNe Ia at z~0.5.