AT2021yky：具有演化宽氢发射的快速上升光学暂现源，符合模糊核暂现源特征
AT2021yky: A Fast-Rising Optical Transient with Evolving Broad Hydrogen Emission Consistent with an Ambiguous Nuclear Transient
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中文总结 AI 辅助
本文研究红移0.076的模糊核暂现源AT2021yky，发现其兼具亮蓝快速光学暂现源与潮汐瓦解事件特征，因温度更低且无额外发射线，归类为模糊核暂现源
中文摘要 AI 辅助
核暂现源是超大质量黑洞性质的有力探针，可用于研究黑洞质量、吸积物理及星系核结构。其中一类事件既无法归类为潮汐瓦解事件（TDE）也不属于活动星系核（AGN）耀发，其物理起源尚不明确。本文对红移z=0.076的模糊核暂现源（ANT）AT2021yky（ZTF21abzciqh）开展多波段测光与光谱分析。AT2021yky的峰值热光度L_peak=(4.1±1.1)×10^43 erg s^-1，上升时标为18.2±0.7天；早期紫外/光学辐射可由温度约1.4×10^4 K的黑体很好拟合，温度低于多数光学选TDE；未探测到该暂现源的X射线辐射，峰值附近3σ极限为L_X≲3.4×10^41 erg s^-1。光谱观测显示，在峰值后20-40天出现具有宽半高全宽（FWHM~11000 km s^-1）的Hα发射线，整体为几乎无特征的蓝连续谱；寄主星系发射线比值表明存在AGN，但缺乏光学或中红外变异性、中红外颜色非AGN特征，说明其较弱。AT2021yky的快速上升时标与亮蓝快速光学暂现源（LFBOT）相当，衰减时标及后期宽Hα发射类似TDE；但它的黑体温度更低，且除Hα外无He II及其他巴耳末发射线，更支持其ANT分类
英文摘要
Nuclear transients are powerful probes of supermassive black hole properties, offering insight into black hole mass, accretion physics, and the structure of galactic nuclei. Among these, a growing class of events cannot be classified as either tidal disruption events (TDEs) or active galactic nuclei (AGN) flares, and their physical origins remain poorly understood. We present a multi-wavelength photometric and spectroscopic analysis of AT2021yky (ZTF21abzciqh), an ambiguous nuclear transient (ANT) at a redshift of $z = 0.076$. AT2021yky reached a peak bolometric luminosity of $L_{\rm peak} = (4.1 \pm 1.1) \times 10^{43}~\mathrm{erg~s^{-1}}$, with a rise-time of $18.2 \pm 0.7$ days. The early-time UV/optical emission is well described by a blackbody with a temperature of $T \simeq 1.4 \times 10^{4}$ K, cooler than most optically selected TDEs. No X-ray emission from the transient is detected, with a $3σ$ limit of $L_X \lesssim 3.4 \times 10^{41}$ erg s$^{-1}$ near peak. Spectroscopic observations reveal a largely featureless blue continuum with broad (FWHM$\sim 11,000$ km s$^{-1}$) H$α$ emission line that appears around 20$-$40 days post-peak. The host-galaxy emission-line ratios indicate the presence of an AGN, though the absence of optical or mid-IR variability and a non-AGN mid-IR color suggest it is weak. AT2021yky exhibits a rapid rise time comparable to that of luminous fast blue optical transients (LFBOTs), while its decay timescale and late-time broad H$α$ emission resemble those observed in TDEs. However, its cooler blackbody temperature and the absence of He II and Balmer emission lines other than H$α$ instead favour its classification as an ANT.
