The four supernovae discovered by the Palomar Transient Factory. Left: before explosion. Right: after explosion. From top to bottom, the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr.

Each tile shows a false-colour image constructed by assigning image data from three separate band passes to red, blue and green (g, r and i bands, respectively, for PTF09atu; u, g or V, and r bands for PTF09cnd, PTF09cwl and PTF10cwr). In each case, Sloan Digital Sky Survey reference data form the pre-explosion image. The post-explosion images are composed from observations made with the Palomar Observatorys 1.5-m telescope, the WISE Observatorys 1.0-m telescope and the Ultraviolet/Optical Telescope on board NASAs Swift satellite.