We report the discovery of a mid-infrared outburst in a Young Stellar Object (YSO) with an amplitude close to 8 mag at $\lambda$$\approx$4.6 $\mu$m. WISEA J142238.82-611553.7 is one of 23 highly variable WISE sources discovered in a search of Infrared Dark Clouds (IRDCs). It lies within the small IRDC G313.671-0.309 (d$\approx$2.6 kpc), seen by the Herschel/HiGal survey as a compact, massive cloud core that may have been measurably warmed by the event. Pre-outburst data from Spitzer in 2004 suggest that it is a class I YSO, a view supported by observation of weak 2.12 $\mu$m H$_2$ emission in an otherwise featureless red continuum spectrum taken in 2019 (6 mag below the peak in K$_s$). Spitzer, WISE and VVV data indicate that the outburst began by 2006 and has a duration $>$13 yr, with a fairly flat peak from 2010--2014. The outburst luminosity of a few $\times 10^2$ Lsun is consistent with an accretion rate Mdot $\approx 10^{-4}$ Msun/yr, comparable to a classical FU Orionis event. The 4.6 $\mu$m peak in 2010 implies T = 800-1000 K and a disc radial location R$\approx$4.5 au for the emitting region. The colour evolution suggests subsequent progression outward. The apparent absence of the hotter matter expected in thermal instability or MRI models may be due to complete obscuration of the innermost disc, e.g. by an edge-on disc view. Alternatively, disc fragmentation/infalling fragment models might more naturally explain a mid-infrared peak, though this is not yet clear.

中文翻译：

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发现异常振幅的中红外原恒星爆发

我们报告了在年轻恒星天体 (YSO) 中发现的中红外爆发，其振幅接近 8 mag，位于 $\lambda$$\approx $4.6 $\mu$m。WISEA J142238.82-611553.7 是在搜索红外暗云 (IRDC) 时发现的 23 个高度可变的 WISE 源之一。它位于小型 IRDC G313.671-0.309（d$\approx$2.6 kpc）内，被 Herschel/HiGal 调查视为一个紧凑的、巨大的云核，可能已被该事件明显变暖。斯皮策在 2004 年的爆发前数据表明它是 I 级 YSO，这一观点得到了 2.12 $\mu$m H$_2$ 微弱发射的支持，该发射在 2019 年拍摄的原本没有特征的红色连续谱中（低于 6 mag K$_s$ 中的峰值）。Spitzer、WISE 和 VVV 的数据表明，爆发始于 2006 年，持续时间 $>$13 年，2010--2014 年的峰值相当平稳。几个 $\times 10^2$ Lsun 的爆发光度与吸积率 Mdot $\approx 10^{-4}$ Msun/yr 一致，可与经典的 FU Orionis 事件相媲美。2010 年的 4.6 $\mu$m 峰值意味着 T = 800-1000 K 和发射区域的盘径向位置 R$\approx $4.5 au。颜色演变表明随后向外发展。热不稳定性或 MRI 模型中预期的较热物质的明显缺失可能是由于最里面的椎间盘完全模糊，例如通过边缘椎间盘视图。或者，光盘碎片/下降碎片模型可能更自然地解释中红外峰，尽管目前尚不清楚。2010 年的 6 $\mu$m 峰值意味着 T = 800-1000 K 和发射区域的圆盘径向位置 R$\approx $4.5 au。颜色演变表明随后向外发展。热不稳定性或 MRI 模型中预期的较热物质的明显缺失可能是由于最里面的椎间盘完全模糊，例如通过边缘椎间盘视图。或者，光盘碎片/下降碎片模型可能更自然地解释中红外峰，尽管目前尚不清楚。2010 年的 6 $\mu$m 峰值意味着 T = 800-1000 K 和发射区域的圆盘径向位置 R$\approx $4.5 au。颜色演变表明随后向外发展。热不稳定性或 MRI 模型中预期的较热物质的明显缺失可能是由于最里面的椎间盘完全模糊，例如通过边缘椎间盘视图。或者，光盘碎片/下降碎片模型可能更自然地解释中红外峰，尽管目前尚不清楚。