ASASSN-13dn: A luminous and double-peaked type II supernova

Abstract

Aims. We present observations of ASASSN-13dn, one of the first supernovae discovered by ASAS-SN, and a new member of the rare group of Luminous Type II Supernovae (LSNe II). It was discovered near maximum light, reaching an absolute magnitude of Mv ∼ -19 mag, placing this object between normal luminosity type II SNe and superluminous SNe Methods. A detailed analysis of the photometric and spectroscopic data of ASASSN-13dn is performed. The spectra are characterized by broad lines, in particular the Hα lines where we measure expansion velocities ranging between 14000 - 6000 km s−1 over the first 100 days. Hα dominates the nebular spectra, and we detect a narrow P-Cygni absorption within the broader emission line with an expansion velocity of 1100 km s−1 . Photometrically, its light curve shows a re-brightening of ∼ 0.6 mag in the gri bands starting at 25±2 days after discovery, with a secondary peak at ∼ 73d, followed by an abrupt and nearly linear decay of 0.09 mag d−1 for the next 35 days. At later times, after a drop of 4 magnitudes from the second maximum, the light curves of ASASSN-13dn shows softer undulations from 125 to 175 days. Results. We compare ASASSN-13dn with other LSNe II in the literature, finding no match to both light curve and spectroscopic properties. We discuss the main powering mechanism and suggest that interaction between the ejecta and a dense CSM produced by eruptions from an LBV-like progenitor could potentially explain the observations.