大质量恒星在富氦的星周介质中爆炸。五.发展缓慢的SN Ibn OGLE-2012-SN-006的观察
Massive stars exploding in a He-rich circumstellar medium. V. Observations of the slow-evolving SN Ibn OGLE-2012-SN-006
摘要：
我们提出了独特的Ibn型超新星（SN Ibn）OGLE-2012-SN-006的光学观测，由OGLE-IV调查发现和监测，并在后期阶段由PESSTO进行光谱跟踪。严格的预发现限制将爆炸时期以相当的精度约束到JD = 2456203.8 +-4.0。I波段光变曲线最大值的上升时间约为两周。该天体在JD = 2456218.1 +- 1.8上达到最高绝对星等M（I）= -19.65 +- 0.19。在最大值之后，光变曲线以每100天4等的速率下降约25天。对称的I带峰类似于典型的Ib/c型超新星（SNe），而SNe Ibn通常表现出不对称和较窄的早期光变曲线。由于25天过去的最大值，光变曲线的下降速度慢于56钴到56铁衰变，虽然在非常晚的阶段，它变陡，以接近该速率。早期的光谱主要是蓝色的连续谱，只有少量的证据表明存在He I线标记这种SN类型。这一光谱显示出比5000 A更蓝的宽反射，可能是O II线，这与早期在超亮SNe中观察到的光谱特征相似。PESSTO在峰值后90 - 180天对该天体进行了光谱监测，这些光谱显示了在一些SN 2006 jc事件中观察到的典型特征，包括蓝色光谱能量分布和突出而狭窄的（v（FWHM）~ 1900 km/s）He I发射线。这表明喷出物与富含氦的星周物质相互作用。在SN喷出物中可能产生的宽（10000 km/s）O I和Ca II特征（包括最新光谱中的[O I] 6300 A，6364 A双峰）的检测支持OGLE-2012-SN-006作为核心塌陷事件的解释。
英文摘要：
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 +- 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 days with a rate of 4 mag per 100d. 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 56Co to 56Fe decay, although at very late phases it steepens to approach that rate. 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 5000A, 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) ~ 1900 km/s) He I emission lines. This suggests that the ejecta are interacting with He-rich circumstellar material. The detection of broad (10000 km/s) O I and Ca II features likely produced in the SN ejecta (including the [O I] 6300A,6364A doublet in the latest spectra) lends support to the interpretation of OGLE-2012-SN-006 as a core-collapse event.
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