Abstract:
We report results of optical imaging and low-resolution spectroscopic monitoring of supernova (SN) 2017iro that
occurred in the nearby (∼31 Mpc) galaxy NGC 5480. The He I λ5876 feature present in the earliest spectrum
(−7 days) classified it as a Type Ib SN. The follow-up observations span from −7 to +266 days with respect to the
B-band maximum. With a peak absolute magnitude in V band MV = −17.76 ± 0.15 mag and bolometric luminosity
log10 L = 42.39 ± 0.09 erg s−1
, SN 2017iro is a moderately luminous Type Ib SN. The overall light-curve
evolution of SN 2017iro is similar to that of SN 2012au and SN 2009jf during the early (up to ∼100 days) and late
phases (>150 days), respectively. The line velocities of both Fe II λ5169 and He I λ5876 are ∼9000 km s−1
near the peak. The analysis of the nebular phase spectrum (∼+209 days) indicates an oxygen mass of ∼0.35 Me.
The smaller [O I]/[Ca II] flux ratio of ∼1 favors a progenitor with a zero-age main-sequence mass in the range
∼13–15 Me, most likely in a binary system, similar to the case of iPTF13bvn. The explosion parameters are
estimated by applying different analytical models to the quasi-bolometric light curve of SN 2017iro. 56Ni mass
synthesized in the explosion has a range of ∼0.05–0.10 Me, ejecta mass ∼1.4–4.3 Me, and kinetic energy
∼(0.8–1.9) × 1051 erg.
