Open Exploration of the Time Domain with the Catalina Real-Time Transient Survey

对时间域的探索——从秒到年的时间尺度变化的物体和现象的发现和研究——现在是天文学中最具活力和发展最快的领域之一，涉及广泛而多样的研究领域，从太阳系和系外行星的发现到遥远的类星体，从恒星天体物理学到宇宙学和极端相对论天体物理学。时域信息对于理解我们观察到的一些最有趣的现象是必不可少的；例如，我们无法从一张超新星的照片或一张伽马射线暴的快照中学到任何东西；恒星的变异性有助于我们理解它们的结构和演化；恒星的运动告诉我们银河系的结构。我们现在把宇宙及其主要成分作为一个动态的、不断变化的系统来研究。信息技术的进步促成了这一变化。多年来，大型数字巡天一直是天文学数据的主要来源。虽然它们可以被看作是全景宇宙摄影，但我们现在正在进入全景宇宙摄影，信息量和质量也相应增加：数字天气巡天可以多次覆盖天空，探测变化或移动的物体和现象。这一趋势将在几年后的大型综合巡天望远镜（LSST）上达到顶峰，但我们已经在用前驱巡天探索时域天文学的科学和技术了。它们已经具有重大的发现潜力，并将帮助我们在未来进行更大规模的调查时提高我们的问题和策略。该项目是卡塔利娜实时瞬变巡天（CRTS）的延续和实质性扩展，这是一项正在进行的、富有成效的天气巡天，它产生了稳定的天文瞬变事件流，并使它们立即可供整个社区使用；这是目前唯一一个这样做的天空调查。它利用由美国宇航局资助的在搜索近地小行星和行星危险小行星时获得的数据流，并利用在软件和数据服务方面的大量现有投资。我们为后续观察和数据分析建立了广泛的合作网络。这些大量的外部资源对NSF来说是免费的，并且提供了比完全资助的新调查更大的科学投资回报。CRTS的总体科学目标是对暗淡多变的天空进行系统的探索。到目前为止，CRTS已经发现了大约6500个不同的瞬变事件和1300万个可变源，包括各种各样的变星、活动星系核、各种宇宙爆炸、恒星耀斑等。至少连续两年，CRTS发表的超新星（SNe）比任何其他调查都要多，包括有史以来最亮的SNe，长期预测的AGN吸积盘的SNe，数百颗矮新星和其他有趣的灾难性变量，白矮星周围的行星，x射线源的新对应物，银河晕中的新潮汐流等。除了大量已知类型的物体和现象之外，还有一种发现以前未知类型的可能性。这个项目将继续这些研究，并开始一些新的研究，这些研究涉及各种开放的天文学挑战。CRTS独特的开放数据政策使整个天文学界都能参与到这些发现中来。所有暂态事件都以电子方式实时发布，所有数据（图像、目录等）也都公开提供；它们将使广泛的档案科学成为可能。CRTS可能是数据共享和重用的一个展示，这必须成为21世纪的标准实践。这个项目将帮助整个天文学界做出新的发现和发展新的科学策略。这是新一代涉及海量数据流实时挖掘和动态后续策略的科学实验的一个例子。我们培养本科生，研究生和博士后，未来的科学和技术的领导者，并制定了各种各样的教育和公共宣传材料，既为新科学和计算。

Exploration of the time domain - discovery and studies of objects and phenomena changing on time scales ranging from seconds to years - is now one of the most vibrant and rapidly developing fields of astronomy, touching on a broad and diverse spectrum of research areas, from the Solar system and discoveries of exoplanets to the distant quasars, and from stellar astrophysics to cosmology and extreme relativistic astrophysics. Time domain information is essential for understanding of some of the most interesting phenomena we observe; for example, we could not learn anything from a single picture of a Supernova, or a single snapshot of a gamma-ray burst; variability of stars aids to our understanding of their structure and evolution; motions of stars tell us about the structure of our Galaxy. We now study the universe and its major constituents as a dynamical, and always changing system. This change was enabled by the progress in information technology. For many years now, large digital sky surveys have been the main sources of data in astronomy. While they can be seen as panoramic cosmic photography, we are now moving into a panoramic cosmic cinematography, with a corresponding increase in information volumes and quality: digital synoptic sky surveys which cover the sky many times, detecting objects and phenomena which change or move. This trend will culminate in the Large Synoptic Survey Telescope (LSST) years from now, but we are already exploring the science and technology of time-domain astronomy with precursor surveys. They already have a significant potential for discovery, and will help us sharpen our questions and strategies for the larger surveys in the future.This project is a continuation and substantial expansion of the Catalina Real-Time Transient Survey (CRTS), an ongoing, productive synoptic sky survey that is producing a steady stream of astronomical transient events, and making them immediately available to the entire community; it is the only current sky survey that does so. It utilizes a data stream obtained in a search for near-Earth and planetary hazard asteroids, funded by NASA, and it leverages considerable existing investments in software and data services. We have established an extensive web of collaborations for the follow-up observations and data analysis. These substantial external resources come at no cost to the NSF, and provide for much greater scientific returns on investment than what could be done with a fully funded, new survey.The overall scientific goal of CRTS is a systematic exploration of the faint, variable sky. CRTS has so far discovered ~6,500 distinct transient events, and 13 million variable sources, including a wide variety of variable stars, active galactic nuclei, various cosmic explosions, stellar flares, etc. For at least 2 years in a row, CRTS has published more Supernovae (SNe) than any other survey, including the most luminous SNe ever seen, long-predicted SNe from AGN accretion disks, hundreds of dwarf novae and other interesting cataclysmic variables, planets around white dwarfs, new counterparts of x-ray sources, new tidal streams in the Galactic halo, etc. In addition to a plenty of known types of objects and phenomena, there is a real possibility of a discovery of previously unknown kinds. This project will continue these studies, and start a number of new ones, that touch on a variety of open astronomical challenges. The unique open data policy of CRTS enables the entire astronomical community to partake in these discoveries. All transient events are published electronically in real time, and all data (images, catalogs, etc.) are also made publicly available; they will enable a broad range of archival science. CRTS may be a showcase for the data sharing and re-use, that must become a standard practice in the 21st century.This project will aid the entire astronomical community in making new discoveries and developing new scientific strategies. It is an example of a new generation of scientific experiments involving real-time mining of massive data streams, and dynamical follow-up strategies. We train undergraduate and graduate students and postdocs, the future science and technology leaders, and develop a broad variety of educational and public outreach materials, both for the new science and computation.