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We present the Palomar Transient Factory discoveries and the photometric andspectroscopic observations of PTF11kmb and PTF12bho. We show that bothtransients have properties consistent with the class of calcium-rich gaptransients, specifically lower peak luminosities and rapid evolution comparedto ordinary supernovae, and a nebular spectrum dominated by [Ca II] emission. Astriking feature of both transients is their host environments: PTF12bho is anintra-cluster transient in the Coma Cluster, while PTF11kmb is located in aloose galaxy group, at a physical offset ~150 kpc from the most likely hostgalaxy. Deep Subaru imaging of PTF12bho rules out an underlying host system toa limit of $M_R > -8.0$ mag, while Hubble Space Telescope imaging of PTF11kmbreveals a marginal counterpart that, if real, could be either a backgroundgalaxy or a globular cluster. We show that the offset distribution of Ca-richgap transients is significantly more extreme than that seen for Type Iasupernovae or even short-hard gamma-ray bursts (sGRBs). Thus, if the offsetsare caused by a kick, they require larger kick velocities and/or longer mergertimes than sGRBs. We also show that almost all Ca-rich gap transients found todate are in group and cluster environments with elliptical host galaxies,indicating a very old progenitor population; the remote locations couldpartially be explained by these environments having the largest fraction ofstars in the intra-group/intra-cluster light following galaxy-galaxyinteractions.

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