SN 1997cy/GRB 970514: A New Piece in the Gamma-Ray Burst Puzzle?

Abstract

We present observations of SN 1997cy, a supernova (SN) discovered as part of the Mount Stromlo Abell Cluster SN Search (Reiss et al.), which does not easily fit into the traditional classification scheme for supernovae. This object's extraordinary optical properties and coincidence with GRB 970514, a short duration gamma-ray burst (GRB), suggest a second case, after SN 1998bw/GRB 980425, for a SN-GRB association. SN 1997cy is among the most luminous SNe yet discovered (MR ≪ -20.1, H0 = 65) and has a peculiar spectrum. We present evidence that SN 1997cy ejected approximately 2.6 M⊙ of56Ni, supported by its late-time light curve and Fe II/[Fe III] lines in its spectrum, although it is possible that both these observations can be explained via circumstellar interaction. While SN 1998bw and SN 1997cy appear to be very different objects with respect to both their gamma-ray and optical properties, SN 1997cy and the optical transient associated with GRB 970508 have roughly similar late-time optical behavior. This similarity may indicate that the late-time optical output of these two intrinsically bright transient events have a common physical process. Although the connection between GRB 970514 and SN 1997cy is suggestive, it is not conclusive. However, if this association is real, follow-up of short duration GRBs detected with BATSE or HETE2 should reveal objects similar to SN 1997cy.