Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey

On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star–black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10−8.56, and has a velocity between 0.18c and 0.21c are disfavored at the 2σ level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4σ level in 95% of future follow-up observations.

2019年8月14日，激光干涉引力波天文台（LIGO）和处女座（Virgo）合作组探测到来自一个黑洞和一个2.6倍太阳质量的致密天体的引力波，这可能是首次中子星 - 黑洞并合。为寻找光学对应体，暗能量巡天（DES）在并合后的0、1、2、3、6和16个夜晚，使用布兰科望远镜/暗能量相机（Blanco/DECam）对整个90%置信水平的定位区域进行了深度成像。DES数据处理管道探测到了不同亮度的天体，我们通过星表匹配、光变曲线特性、宿主星系的光度红移、南方天体物理研究（Southern Astrophysical Research）的光谱后续观测以及基于机器学习的光度分类，系统地筛选了候选对应体。所有候选体都被排除为并合的对应体。为了量化我们搜索的敏感度，我们将选择标准应用于超新星和千新星在暗能量相机观测中可能出现的完整光变曲线模拟。由于并合的源类别不确定，如果并合包含中子星，我们基于潮汐瓦解的中子星（NS）抛射物特性使用了一种不可知的三分量千新星模型来量化我们对对应体的探测效率。我们发现，如果在这次并合过程中发生了千新星现象，那么在2倍标准差水平下，不支持抛射物质大于0.07倍太阳质量、镧系元素丰度小于10⁻⁸.⁵⁶且速度在0.18c到0.21c之间的配置。此外，我们估计我们的背景减除方法能够在未来95%的后续观测中，在4倍标准差水平上将引力波信号与探测到的电磁对应体相关联。