PS1-10bzj: A fast, hydrogen-poor superluminous supernova in a metal-poor host galaxy

We present observations and analysis of PS1-10bzj, a superluminous supernova (SLSN) discovered in the Pan-STARRS Medium Deep Survey at a redshift z = 0.650. Spectroscopically, PS1-10bzj is similar to the hydrogen-poor SLSNe 2005ap and SCP 06F6, though with a steeper rise and lower peak luminosity (M_bol ≃ -21.4 mag) than previous events. We construct a bolometric light curve, and show that while PS1-10bzj's energetics were less extreme than previous events, its luminosity still cannot be explained by radioactive nickel decay alone. We explore both a magnetar spin-down and circumstellar interaction scenario and find that either can fit the data. PS1-10bzj is located in the Extended Chandra Deep Field South and the host galaxy is imaged in a number of surveys, including with the Hubble Space Telescope. The host is a compact dwarf galaxy (M_B ≈ -18 mag, diameter ≲ 800 pc), with a low stellar mass (M_* ≈ 2.4 × 10⁷ M_odot;), young stellar population (τ_* ≈ 5 Myr), and a star formation rate of ∼2-3 M_odot;yr^-1. The specific star formation rate is the highest seen in an SLSN host so far (∼100 Gyr^-1). We detect the [O III] λ4363 line, and find a low metallicity: 12 + (O/H) = 7.8 ± 0.2 (≃ 0.1 Z_odot;). Together, this indicates that at least some of the progenitors of SLSNe come from young, low-metallicity populations.