The tidal disruption event AT 2018hyz – I. Double-peaked emission lines and a flat Balmer decrement
The tidal disruption event AT 2018hyz – I. Double-peaked emission lines and a flat Balmer decrement
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DOI：
10.1093/mnras/staa2065
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发表时间：
2020-03
影响因子：
4.8
通讯作者：
P. Short;M. Nicholl;M. Nicholl;Andy Lawrence;S. Gomez;I. Arcavi;I. Arcavi;T. Wevers;G. Leloudas;S. Schulze;Joseph P. Anderson;E. Berger;P. Blanchard;J. Burke;J. Burke;N. C. Segura;P. Charalampopoulos;R. Chornock;L. Galbany;M. Gromadzki;L. Herzog;D. Hiramatsu;D. Hiramatsu;K. Horne;G. Hosseinzadeh;D. Howell;D. Howell;N. Ihanec;C. Inserra;E. Kankare;Kate Maguire;C. McCully;T. M. Bravo;F. Onori;J. Sollerman;D. Young
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文献类型：
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作者：
P. Short;M. Nicholl;M. Nicholl;Andy Lawrence;S. Gomez;I. Arcavi;I. Arcavi;T. Wevers;G. Leloudas;S. Schulze;Joseph P. Anderson;E. Berger;P. Blanchard;J. Burke;J. Burke;N. C. Segura;P. Charalampopoulos;R. Chornock;L. Galbany;M. Gromadzki;L. Herzog;D. Hiramatsu;D. Hiramatsu;K. Horne;G. Hosseinzadeh;D. Howell;D. Howell;N. Ihanec;C. Inserra;E. Kankare;Kate Maguire;C. McCully;T. M. Bravo;F. Onori;J. Sollerman;D. Young
我们展示了对AT 2018hyz的光谱观测结果，AT 2018hyz是超新星全天自动巡天发现的一颗瞬态恒星，绝对星等为MV ~ - 20.2等，位于一个具有强巴尔默吸收线的静止星系的核心。AT 2018hyz显示出蓝色连续光谱和宽发射线，与之前的TDE候选者一致。高节奏的后续光谱在早期光谱中显示出宽的Balmer线和He i， He ii在~ 70-100 d后出现。Balmer线从光滑的宽剖面演变，经过与吸积盘发射一致的方形、不对称双峰相位，并在后期恢复到光滑。巴尔默谱线与典型的活动星系核不同，它们表现出平坦的巴尔默衰减（Hα/Hβ ~ 1.5），这表明这些谱线是碰撞激发的，而不是通过光电离产生的。平坦的巴尔默衰减和复杂的轮廓表明，发射线起源于盘状色球，类似于在灾变变量中看到的那些。由于可能的局部破坏，材料的低光学深度可能使我们能够观察到这些双峰碰撞激发线。He ii的出现较晚可能是由于膨胀的光球或外流，或在碎片碰撞中较晚的冲击。
We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of MV ∼ −20.2 mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He i in early spectra, with He ii making an appearance after ∼70–100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (Hα/Hβ ∼ 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He ii may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.