Photometric typing analyses of three young supernovae observed with the robotic Palomar 60 inch telescope

We present photometric typing analyses of three young supernovae observed with the robotic 60 inch (1.5 m) telescope at Palomar Observatory (P60). This represents the first time that such phototyping, conducted in a blind fashion, has been attempted on newly discovered supernovae. For one of the target supernovae, SN 2004cs, our photometry provided the first constraint on the supernova type, which we predicted would be Type Ia. Contrary to expectations, however, our subsequent Keck spectroscopy shows it to be an unusual Type II supernova. For each of the other two supernovae (SN 2004dh [Type II] and SN 2004dk [Type Ib]), our phototyping results are consistent with the known event type as determined from ground-based spectroscopy. However, the colors of SN 2004dk are also consistent with a Type Ic or Type II classification. We discuss our approach to the challenges of phototyping-contamination by host galaxy light and the unknown photometric quality of the data-for cases in which it is desirable to complete the analysis with just one night of observations. The growing interest in the properties and behavior of very young supernovae, and the increased discovery rate for such events, mean that prompt phototyping analyses can provide useful input for observational campaigns. Our results demonstrate the value and feasibility of such a project for P60, at the same time illustrating its chief inherent shortcoming: an inability to identify new and unusual events as such without later spectroscopic observations.