Massive stars exploding in a He-rich circumstellar medium. V. Observations of the slow-evolving SN Ibn OGLE-2012-SN-006

PASTORELLO ; WYRZYKOWSKI; VALENTI; PRIETO; KOZLOWSKI; UDALSKI; ELIAS-ROSA; MORALES-GAROFFOLO; ANDERSON; BENETTI; BERSTEN

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015 vol. 449

0035-8711

We present optical observations of the peculiar Type Ibn supernova (SNIbn) OGLE-2012-SN-006, discovered and monitored by the OGLE-IV survey,and spectroscopically followed by PESSTO at late phases. Stringentpre-discovery limits constrain the explosion epoch with fair precisionto JD = 2456203.8 +- 4.0. The rise time to the I-band light curvemaximum is about two weeks. The object reaches the peak absolutemagnitude M(I) = -19.65 +- 0.19 on JD = 2456218.1 +- 1.8. Aftermaximum, the light curve declines for about 25 days with a rate of 4mag per 100d. The symmetric I-band peak resembles that of canonicalType Ib/c supernovae (SNe), whereas SNe Ibn usually exhibit asymmetricand narrower early-time light curves. Since 25 days past maximum, thelight curve flattens with a decline rate slower than that of the 56Coto 56Fe decay, although at very late phases it steepens to approachthat rate. An early-time spectrum is dominated by a blue continuum,with only a marginal evidence for the presence of He I lines markingthis SN Type. This spectrum shows broad absorptions bluewards than5000A, likely O II lines, which are similar to spectral featuresobserved in super-luminous SNe at early epochs. The object has beenspectroscopically monitored by PESSTO from 90 to 180 days after peak,and these spectra show the typical features observed in a number of SN2006jc-like events, including a blue spectral energy distribution andprominent and narrow (v(FWHM) ~ 1900 km/s) He I emission lines. Thissuggests that the ejecta are interacting with He-rich circumstellarmaterial. The detection of broad (10000 km/s) O I and Ca II featureslikely produced in the SN ejecta (including the [O I] 6300A,6364Adoublet in the latest spectra) lends support to the interpretation ofOGLE-2012-SN-006 as a core-collapse event.