|
Description
We present optical observations of the peculiar Type Ibn supernova (SN Ibn) OGLE-2012-SN-006, discovered and monitored by the Optical Gravitational Lensing Experiment-IV survey, and spectroscopically followed by Public ESO Spectroscopic Survey of Transient Objects (PESSTO) at late phases. Stringent pre-discovery limits constrain the explosion epoch with fair precision to JD=2456203.8+/-4.0. The rise time to the I-band light-curve maximum is about two weeks. The object reaches the peak absolute magnitude M_I_=-19.65+/-0.19 on JD=2456218.1+/-1.8. After maximum, the light curve declines for about 25 d with a rate of 4 mag (100 d)^-1^. The symmetric I-band peak resembles that of canonical Type Ib/c supernovae (SNe), whereas SNe Ibn usually exhibit asymmetric and narrower early-time light curves. Since 25 d past maximum, the light curve flattens with a decline rate slower than that of the ^56^Co-^56^Fe decay, although at very late phases it steepens to approach that rate. However, other observables suggest that the match with the ^56^Co decay rate is a mere coincidence, and the radioactive decay is not the main mechanism powering the light curve of OGLE-2012-SN-006. An early-time spectrum is dominated by a blue continuum, with only a marginal evidence for the presence of HeI lines marking this SN type. This spectrum shows broad absorptions bluewards than 5000 {AA}, likely OII lines, which are similar to spectral features observed in superluminous SNe at early epochs. The object has been spectroscopically monitored by PESSTO from 90 to 180 d after peak, and these spectra show the typical features observed in a number of SN 2006jc-like events, including a blue spectral energy distribution and prominent and narrow ({nu}_FWHM_~1900 km/s) HeI emission lines. This suggests that the ejecta are interacting with He-rich circumstellar material. The detection of broad (10^4^ km/s) OI and CaII features likely produced in the SN ejecta (including the [OI] {lambda}{lambda}6300,6364 doublet in the latest spectra) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event.
|
