Dust Echoes from Luminous Fast Blue Optical Transients
Dust Echoes from Luminous Fast Blue Optical Transients
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DOI：
10.3847/1538-4357/acae89
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
B. Metzger;D. Perley
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文献类型：
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作者：
B. Metzger;D. Perley
像AT 2018 cow这样的发光快速蓝色光学瞬变（LFBOTs）形成了一类罕见的发动机驱动爆炸，其起源不明。这些事件的一个标志性特征是射电/毫米波同步辐射，由快速的0.1c喷出物和致密的拱星物质（CSM）的相互作用提供动力，这些物质延伸到祖星周围的大半径1016厘米。假设这个CSM是从祖先流出的，我们表明，在爆炸前的几年里，在流出物中可以形成直径达101 μm的尘埃颗粒。这种尘埃CSM会在峰值光之前衰减瞬态的紫外发射，然后被上升的光度破坏，使最大值前的颜色变红（与LFBOT候选者MUSSES 2020 J的最大值前的红色到蓝色演变一致）。尘埃在被摧毁前的再辐射会产生一个亮度为1041-1042 erg s−1的近红外（NIR）“回波”，持续数周，这在瞬变快速衰减的蓝色连续光谱中是可以探测到的。我们发现，这种尘埃回波与之前在AT 2018 cow中观察到的无法解释的NIR过量是相容的。早期近红外光变曲线的逐渐衰减可能是由于CSM，它集中在广角赤道流出或环面，与AT 2018奶牛喷出物的高度非球面几何形状一致。LFBOTs的预最大光学/UV和NIR后续行动提供了一个新的探测其CSM环境，并对其祖先施加额外的限制。
Luminous fast blue optical transients (LFBOTs) such as AT2018cow form a rare class of engine-powered explosions of uncertain origin. A hallmark feature of these events is radio/millimeter synchrotron emission powered by the interaction of fast ≳0.1c ejecta and dense circumstellar material (CSM) extending to large radii ≳1016 cm surrounding the progenitor. Assuming this CSM to be an outflow from the progenitor, we show that dust grains up to ∼1 μm in size can form in the outflow in the years before the explosion. This dusty CSM would attenuate the transient’s ultraviolet emission prior to peak light, before being destroyed by the rising luminosity, reddening the premaximum colors (consistent with the premaximum red-to-blue color evolution of the LFBOT candidate MUSSES2020J). Reradiation by the dust before being destroyed generates a near-infrared (NIR) “echo” of luminosity ∼1041–1042 erg s−1 lasting weeks, which is detectable over the transient’s rapidly fading blue continuum. We show that this dust echo is compatible with the previously unexplained NIR excess observed in AT2018cow. The gradual decay of the early NIR light curve can result from CSM, which is concentrated in a wide-angle equatorial outflow or torus, consistent with the highly aspherical geometry of AT2018cow’s ejecta. Premaximum optical/UV and NIR follow-up of LFBOTs provide a new probe of their CSM environments and place additional constraints on their progenitors.