The Blue Supergiant Progenitor of the Supernova Imposter AT 2019krl
The Blue Supergiant Progenitor of the Supernova Imposter AT 2019krl
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DOI：
10.3847/1538-4357/ac09e1
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发表时间：
2020-09
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通讯作者：
J. Andrews;J. Jencson;S. V. van Dyk;N. Smith;J. Neustadt;D. Sand;K. Kreckel;C. Kochanek;S. Va
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作者：
J. Andrews;J. Jencson;S. V. van Dyk;N. Smith;J. Neustadt;D. Sand;K. Kreckel;C. Kochanek;S. Va
哈勃太空望远镜、斯皮策太空望远镜和大型双目望远镜对 M74 中近期中等光度瞬变 AT 2019krl 的大量档案显示，揭示了一颗明亮的光学和中红外祖星。虽然错过了该事件的光学峰值，但在红外中检测到绝对星等为 M 4.5 μm = -18.4 星等的峰值，这使我们推断出可见光波长峰值绝对星等为 -13.5 至 -14.5。发现前的光曲线表明过去 16 年没有爆发。如果仅考虑前景消光，则祖星的颜色、星等和推断温度与 13–14 M ⊙ 黄超或蓝超巨星 (BSG) 最匹配，如果考虑任何额外的局部消光，则与更热、质量更大的恒星最匹配。恒星爆发前的光谱显示出强烈的 Hα 和 [N ii] 发射，其翼延伸至 ±2000 km s−1。喷发后的光谱相当平坦且无特征，仅发射 Hα、Na i D、[Ca ii] 和 Ca ii 三重态。与之前许多中等光度瞬变一样，AT 2019krl 在观测上与发光蓝变星 (LBV) 巨喷发、SN 2008S 类似事件和大质量恒星合并表现出显着的相似性。然而，有关爆发前恒星的信息要么支持相对不被遮挡的 BSG，要么支持 M > 20 M⊙ 可能在极点上观察到的更熄灭的 LBV。
Extensive archival Hubble Space Telescope, Spitzer Space Telescope, and Large Binocular Telescope imaging of the recent intermediate-luminosity transient, AT 2019krl in M74, reveal a bright optical and mid-infrared progenitor star. While the optical peak of the event was missed, a peak was detected in the infrared with an absolute magnitude of M 4.5 μm = −18.4 mag, leading us to infer a visual-wavelength peak absolute magnitude of −13.5 to −14.5. The pre-discovery light curve indicated no outbursts over the previous 16 yr. The colors, magnitudes, and inferred temperatures of the progenitor best match a 13–14 M ⊙ yellow or blue supergiant (BSG) if only foreground extinction is taken into account, or a hotter and more massive star if any additional local extinction is included. A pre-eruption spectrum of the star reveals strong Hα and [N ii] emission with wings extending to ±2000 km s−1. The post-eruption spectrum is fairly flat and featureless with only Hα, Na i D, [Ca ii], and the Ca ii triplet in emission. As in many previous intermediate-luminosity transients, AT 2019krl shows remarkable observational similarities to luminous blue variable (LBV) giant eruptions, SN 2008S-like events, and massive-star mergers. However, the information about the pre-eruption star favors either a relatively unobscured BSG or a more extinguished LBV with M > 20 M⊙ likely viewed pole-on.