Two New Calcium-Rich Gap Transients in Group and Cluster Environments

Understand

We present the Palomar Transient Factory discoveries and the photometric and spectroscopic observations of PTF11kmb and PTF12bho.

• We show that both transients have properties consistent with the class of calcium-rich gap transients, specifically lower peak luminosities and rapid evolution compared to ordinary supernovae, and a nebular spectrum dominated by [Ca II] emission.
• A striking feature of both transients is their host environments: PTF12bho is an intra-cluster transient in the Coma Cluster, while PTF11kmb is located in a loose galaxy group, at a physical offset ~150 kpc from the most likely host galaxy.
• Deep Subaru imaging of PTF12bho rules out an underlying host system to a limit of $M_R > -8.0$ mag, while Hubble Space Telescope imaging of PTF11kmb reveals a marginal counterpart that, if real, could be either a background galaxy or a globular cluster.