The highly luminous Type Ibn supernova ASASSN-14ms

We present photometric and spectroscopic follow-up observations of the highly luminous Type Ibn supernova ASASSN-14ms, which was discovered on UT 2014-12-26.61 at m_V ∼ 16.5. With a peak absolute V-band magnitude brighter than -20.5, a peak bolometric luminosity of 1.7 × 10⁴⁴ erg s^-1, and a total radiated energy of 2.1 × 10⁵⁰ erg, ASASSN-14ms is one of the most luminous Type Ibn supernovae yet discovered. In simple models, the most likely power source for this event is a combination of the radioactive decay of ⁵⁶Ni and ⁵⁶Co at late times and the interaction of supernova ejecta with the progenitor's circumstellar medium at early times, although we cannot rule out the possibility of a magnetar-powered light curve. The presence of a dense circumstellar medium is indicated by the intermediate-width He I features in the spectra. The faint (m_g ∼ 21.6) host galaxy SDSS J130408.52+521846.4 has an oxygen abundance below 12 + log (O/H) ≲ 8.3, a stellar mass of M_* ∼ 2.6 × 10⁸ M_⊙, and a star formation rate of SFR ∼ 0.02 M_⊙ yr^-1.