非常年轻的Ia型超新星2012 cg：发现和早期跟踪观测
The Very Young Type Ia Supernova 2012cg: Discovery and Early-Time Follow-Up Observations
摘要：
2012年5月17.2 UT，在爆发后1.5 ± 0.2 d，我们在NGC 4424（d ~ 15 Mpc）中发现了一颗Ia型超新星SN 2012 cg。由于利克天文台SN搜索采用了新修改的策略，在发现后161秒开始获得了一系列过滤图像。利用最近的模型描述的SN喷出物与伴星的相互作用，我们排除了一个~1 M_太阳伴星的一半的所有视角和红巨星伴星几乎所有的方向。SN 2012 cg在2012年6月2.0日达到B波段最大值12.09 +/- 0.02等，从爆炸到达到这个值花了约17.3天，这是典型的超新星Ia。我们的预最大亮度测光显示SN 2012 cg的B波段光变曲线比平均值窄，尽管在最大亮度时稍微过亮，颜色演变正常（包括一些最早的SN Ia过滤测光）。SN 2012 cg的光谱拟合揭示了在超新星Ia早期发现的典型离子，在爆炸后2.5 d时的膨胀速度> 14，000 km/s。从C II吸收早期检测，以及高速组件的Si II 6355 Ang。Ca II。我们的最后一个光谱（爆炸后13.5天）类似于有点奇特的SN Ia 1999 aa。这表明SN 2012 cg的光变曲线下降速度慢于平均值，考虑到光变曲线上升速度快于平均值，这可能令人惊讶。
英文摘要：
On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN 2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of the newly modified strategy employed by the Lick Observatory SN Search, a sequence of filtered images was obtained starting 161 s after discovery. Utilizing recent models describing the interaction of SN ejecta with a companion star, we rule out a ~1 M_Sun companion for half of all viewing angles and a red-giant companion for nearly all orientations. SN 2012cg reached a B-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from explosion to reach this, typical for SNe Ia. Our pre-maximum brightness photometry shows a narrower-than-average B-band light curve for SN 2012cg, though slightly overluminous at maximum brightness and with normal color evolution (including some of the earliest SN Ia filtered photometry ever obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at early times, with expansion velocities >14,000 km/s at 2.5 d past explosion. Absorption from C II is detected early, as well as high-velocity components of both Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion) resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN 2012cg will have a slower-than-average declining light curve, which may be surprising given the faster-than-average rising light curve.
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