从“初光”开始:FAST早期科学及前景展望

Shining on from the first light:The early sciences of FAST

国家大科学装置500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope,FAST)在2016年9月19日获得"初光"(first-light).FAST从20世纪90年代中期概念提出,2011年3月开工,2019年征集风险共担的开放项目,到2020年成功通过国家验收、开展重大优先及开放项目的观测,正式进入常规运行.这20多年的长征,FAST团队一再面对高速发展的射电天文技术和科学前沿带来的挑战.

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is a Chinese mega-science project, the first light of which was achieved on September 19 th, 2016. The mid-1990 s witnessed the birth of the FAST concept, March of 2011 the commencement of construction, 2019 the shared-risk open programs, and 2020 the final project review, first batch of major surveys and the starting of normal operation. Throughout the more than two decades’ "long march", there has never been a lack of constant struggle and challenges, brought about by the fast-moving frontiers of radio technology and radio astronomy. This is a brief summary of our innovations in response, including a low-cost ultra-wideband commissioning receiver, a highly configurable digital spectrometer, a container-based data center, a fast radio burst(FRB) backend, etc.During the early science phase, we developed the world’s first commensal observing mode in this band, capable of recording pulsar, Galactic HI, extra-galactic HI, and transient data streams, simultaneously. The thus based Commensal Radio Astronomy FAST Survey(CRAFTS) was approved as one of the five major surveys by the science committee and has produced the first batch of FAST’s science results, including new pulsars, new FRBs, the first paper on systematic timing of FAST new pulsars, etc. Before CRAFTS, there is no major survey that accomplished simultaneously searching for pulsars and imaging HI. CRAFTS helps improve the survey efficiency of FAST by more than three folds. In addition to surveys, FAST has started more than 100 PI-led programs, selected by open competitions through the "shared-risk" and the first open call for proposals. Many proposals focused on new frontiers, such as FRBs and exoplanets. FAST joined the campaign to monitor the only Galactic FRB source J1935+2154 and provided the most stringent constraint on its radio flux,which is crucial to understand the origin of FRBs. This result along with the discovery papers has been cited as one of the major scientific achievements world-wide in 2020.The cost per unit effective collecting area of FAST is only 1/4 that of the Greenbank Telescope(GBT) or the Square Kilometer Array-phase 1(SKA1). The success of FAST demonstrates that a giant filled-aperture antenna can still be the most cost-effective route toward the best absolute sensitivity. In light of the main stream of radio astronomy development toward powerful arrays, however, FAST will have to continue exploiting its upgradability, which is another major advantage of a giant single dish over interferometers. For an interferometer of n element, any major upgrade will incur cost of ~n sets of electronics and of ~n2 computational costs. For FAST, a cooled PAF is its clear land-mark goal, which will help utilize its relatively flat and spacious focal plane to achieve even better survey efficiency and quality.Human’s worldview and cosmos-view have been entirely shaped by what we can observe. The ultimate goal of FAST is to deepen mankind’s understanding of nature through worldview-altering discoveries. On December 1 st, 2020 local time,the great Arecibo telescope, after occupying the world’s apex of radio sensitivity for more than half a century, collapsed.The FAST was inspired by the audacity of Arecibo and encouraged by its achievements. As envisioned by Dr. Nan,Rendong, "FAST represents the collective ambition of Chinese astronomers to leap from chasing to leading." It starts now.