GALEX和CFHTLS对潮汐扰动事件的紫外/光学探测
UV/Optical Detections of Candidate Tidal Disruption Events by GALEX and CFHTLS
摘要：
我们提出了两个发光的UV/光学耀斑从显然不活跃的早型星系的核在z=0.37和0.33，具有从恒星的潮汐破裂耀斑的辐射特性。在本文中，我们报告的第二个候选人潮汐中断事件发现的紫外线的GALEX深成像调查，并提出同时从CFHTLS深成像调查的紫外耀斑的光学光变曲线。最初几个月的紫外/可见光变光曲线很好地拟合了典型的t^（-5/3）幂律衰减，这是对潮汐破裂恒星碎片回落所产生的辐射的预测。钱德拉ACIS在耀斑期间的X射线观测发现了T_bb=（2-5）x 10^5 K或Gamma > 3的软X射线源，并将来自下面活动星系核的硬X射线发射限制在L_X（2-10 keV）<~ 10^41 ergs/s。黑体对耀斑紫外/光学光谱能量分布的拟合表明，耀斑的峰值亮度大于10^44-10^45尔格/秒。这两个耀斑的温度、光度和光变曲线都与从潮汐破裂的主序星发射到中心黑洞（质量是10^7 msun的几倍）上的辐射非常吻合。我们在2003年至2007年期间对GALEX深度成像调查数据进行的~ 2.9 deg^2搜索中观察到的探测率与根据动力学模型计算的潮汐中断率一致，我们使用这些模型对下一代光学天气调查的探测率进行预测。
英文摘要：
We present two luminous UV/optical flares from the nuclei of apparently inactive early-type galaxies at z=0.37 and 0.33 that have the radiative properties of a flare from the tidal disruption of a star. In this paper we report the second candidate tidal disruption event discovery in the UV by the GALEX Deep Imaging Survey, and present simultaneous optical light curves from the CFHTLS Deep Imaging Survey for both UV flares. The first few months of the UV/optical light curves are well fitted with the canonical t^(-5/3) power-law decay predicted for emission from the fallback of debris from a tidally disrupted star. Chandra ACIS X-ray observations during the flares detect soft X-ray sources with T_bb= (2-5) x 10^5 K or Gamma > 3 and place limits on hard X-ray emission from an underlying AGN down to L_X (2-10 keV) <~ 10^41 ergs/s. Blackbody fits to the UV/optical spectral energy distributions of the flares indicate peak flare luminosities of > 10^44-10^45 ergs/s. The temperature, luminosity, and light curves of both flares are in excellent agreement with emission from a tidally disrupted main sequence star onto a central black hole of several times 10^7 msun. The observed detection rate of our search over ~ 2.9 deg^2 of GALEX Deep Imaging Survey data spanning from 2003 to 2007 is consistent with tidal disruption rates calculated from dynamical models, and we use these models to make predictions for the detection rates of the next generation of optical synoptic surveys.
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