AI 中文总结
研究AT2018cow紫外/光学平台影响，提出其紫外/光学发射源于内盘超爱丁顿风光球层及外盘作用，通过拟合多波段数据发现不同质量吸积体拟合效果类似，近红外 - 中红外发射及复合线发射或可判别吸积体质量等，模型参数与微潮汐破坏事件相符。
AI 中文摘要
典型的明亮快速蓝光学瞬变源（LFBOT）AT2018cow在爆炸后至少5年的紫外/光学波段显示出缓慢衰减的平台期。该平台期的SED类似黑体，温度$\gtrsim$ 2e4 K，发射半径约40太阳半径，这被归因于围绕致密天体的几何薄吸积盘。然而，粘性驱动的盘模型需要一个异常大质量的黑洞$\gtrsim$ 200太阳质量（对于粘性参数$\alpha$ > 0.01）。此外，除非X射线高度各向异性或被吸收，否则吸积到如此大质量黑洞上产生的X射线发射可能与XMM - Newton的约束相矛盾。我们提出紫外/光学发射来自内盘发射的超爱丁顿风的光球层，以及几何薄外盘的辐照和再处理。将模型与t ~ 4年时的四波段HST测光数据拟合，我们发现从1.4太阳质量的中子星到约100太阳质量的黑洞的所有吸积体都能产生类似的良好拟合。这种简并性的出现是因为风光球层的色温度仅微弱地依赖于吸积体质量。我们还发现，在近红外 - 中红外波长（1至10微米），风的自由 - 自由发射在允许的质量范围内相差一个数量级，这为JWST提供了一个潜在的判别方法。另一个区分吸积体质量和盘成分的潜在特征是盘风的复合线发射（HeII1640或H$\alpha$）。我们模型推断出的盘参数与微潮汐破坏事件一致，即潮汐破坏或与伴星合并，其中最初几何厚的盘在第一年内转变为薄盘，随后薄外盘在观测到的约10年粘性时间尺度上演化。
英文摘要
AT2018cow, the prototypical luminous fast blue optical transient (LFBOT), shows a slowly fading plateau in the UV/optical light lasting at least 5 years after the explosion. The plateau SED is blackbody-like with temperature $\gtrsim$ 2e4 K and an emission radius ~40 Rsun, which has been attributed to a geometrically thin accretion disk around a compact object. Viscously powered disk models, however, require an unusually massive black hole $\gtrsim$ 200 Msun (for viscosity parameter $α$ > 0.01). Moreover, accretion onto such a massive black hole produces X-ray emission that is likely in tension with the XMM-Newton constraint, unless the X-ray is highly anisotropic or absorbed. We propose instead that the UV/optical emission arises from the photosphere of a super-Eddington wind launched from the inner disk, together with irradiation and reprocessing by the geometrically thin outer disk. Fitting the model to four-band HST photometry at t ~ 4 yr, we find that all accretors from 1.4 Msun neutron star to ~100 Msun black hole produce similarly good fits. This degeneracy arises because the wind photospheric color temperature depends only weakly on the accretor mass. We also find that, at NIR-MIR wavelengths (1 to 10 um), wind free-free emission differs by an order of magnitude across the allowed mass range, providing a potential discriminant accessible to JWST. Another potential signature to differentiate the accretor mass and disk composition is the recombination line emission (HeII1640 or H$α$) from the disk wind. The inferred disk parameters from our model are consistent with a micro-tidal disruption event, either tidal disruption or merger with a companion star, in which an initially geometrically thick disk transitions to a thin phase within the first year and subsequently the thin outer disk evolves on the observed ~10 yr viscous timescale.
Comments15 pages, 5 figures, plus appendix. Comments, big or small, are very welcome!
