We present optical observations of the peculiar Type Ibn supernova ( SN Ibn ) OGLE-2012-SN-006 , discovered and monitored by the OGLE - IV survey , and spectroscopically followed by PESSTO at late phases .
Stringent pre-discovery limits constrain the explosion epoch with fair precision to JD = 2456203.8 \pm 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 \pm 0.19 on JD = 2456218.1 \pm 1.8 .
After maximum , the light curve declines for about 25 days with a rate of 4 mag 100d ^ { -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 days past maximum , the light curve flattens with a decline rate slower than that of the ^ { 56 } Co to ^ { 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 He I lines marking this SN Type .
This spectrum shows broad absorptions bluewards than 5000Å , likely O II lines , which are similar to spectral features observed in super-luminous SNe at early epochs .
The object has been spectroscopically monitored by PESSTO from 90 to 180 days 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 ( v _ { FWHM } \approx 1900 km s ^ { -1 } ) He I emission lines .
This suggests that the ejecta are interacting with He-rich circumstellar material .
The detection of broad ( 10 ^ { 4 } km s ^ { -1 } ) O I and Ca II features likely produced in the SN ejecta ( including the [ O I ] \lambda \lambda 6300,6364 doublet in the latest spectra ) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event .