SN 2015 bn的一千天：HST成像显示与磁星预测一致的光变曲线平坦
One thousand days of SN 2015bn: HST imaging shows a light curve flattening consistent with magnetar predictions
摘要：
我们提出了第一次观察到的I型超亮超新星（SLSN）在$\gtrsim 1000$天后，最大的光。我们使用哈勃太空望远镜高级巡天相机在F475 W，F625 W和F775 W过滤器中观察SN 2015 bn，分别为721天和1068天。SN 2015 bn被清楚地探测到，并从其紧凑的主机中分辨出来，从而可以进行可靠的测光。从这些数据构建的星系模板进一步使我们能够隔离SLSN通量在深地面成像。我们测量的光变曲线下降率在$>700$天的$0.19 \pm 0.03$ mag（100天）$^{-1}$，比早期的演变浅得多，比以前的SLSNe（在任何阶段）或$^{56}$公司的衰变率慢。无论是额外的放射性同位素，也没有光回波可以始终占缓慢下降。1083天的光谱显示了与$\sim300-400$天相同的[O I]和[Ca II]线，没有新的特征表明强烈的星周相互作用。甚大天线阵的无线电限制排除了质量损失率$10^{-2.7} \lesssim \dot{M}/v_{10} \lesssim 10^{-1.1}$ M $_\odot$ yr $^{-1}$的扩展风（其中$v_{10}$是风速，单位为10 km s $^{-1}$）。的光学光变曲线是一致的$L \propto t^{-4}$，这是我们预期的磁星自旋与效率低下的陷阱，此外，演变匹配的预测，从早期的磁星模型拟合。对磁星辐射的不透明度被限制在$\sim 0.01$ cm $^2$ g $^{-1}$，与在广泛的$\sim$ GeV-TeV范围内的光子-物质对生产一致。这表明磁星的光谱能量分布，因此从喷出物泄漏的“丢失的能量”可能在这个范围内达到峰值。
英文摘要：
We present the first observations of a Type I superluminous supernova (SLSN) at $\gtrsim 1000$ days after maximum light. We observed SN 2015bn using the Hubble Space Telescope Advanced Camera for Surveys in the F475W, F625W and F775W filters at 721 days and 1068 days. SN 2015bn is clearly detected and resolved from its compact host, allowing reliable photometry. A galaxy template constructed from these data further enables us to isolate the SLSN flux in deep ground-based imaging. We measure a light curve decline rate at $>700$ days of $0.19 \pm 0.03$ mag (100 d)$^{-1}$, much shallower than the earlier evolution, and slower than previous SLSNe (at any phase) or the decay rate of $^{56}$Co. Neither additional radioactive isotopes nor a light echo can consistently account for the slow decline. A spectrum at 1083 days shows the same [O I] and [Ca II] lines as seen at $\sim300-400$ days, with no new features to indicate strong circumstellar interaction. Radio limits with the Very Large Array rule out an extended wind for mass-loss rates $10^{-2.7} \lesssim \dot{M}/v_{10} \lesssim 10^{-1.1}$ M$_\odot$ yr$^{-1}$ (where $v_{10}$ is the wind velocity in units of 10 km s$^{-1}$). The optical light curve is consistent with $L \propto t^{-4}$, which we show is expected for magnetar spin-down with inefficient trapping; furthermore, the evolution matches predictions from earlier magnetar model fits. The opacity to magnetar radiation is constrained at $\sim 0.01$ cm$^2$ g$^{-1}$, consistent with photon-matter pair-production over a broad $\sim$GeV-TeV range. This suggests the magnetar spectral energy distribution, and hence the 'missing energy' leaking from the ejecta, may peak in this range.
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