Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University, Ithaca, New York 14853, USA.
Department of Astronomy and Radio Astronomy Lab, University of California, Berkeley, California 94720, USA.
Nature. 2017 Jan 4;541(7635):58-61. doi: 10.1038/nature20797.
Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.
快速射电暴是一种未知物理性质的天体无线电闪光，持续时间为毫秒级。它们的色散到达时间表明其具有星系际起源，并暗示其射电亮度比所有已知的短持续时间的射电瞬变体大几个数量级。到目前为止，所有的快速射电暴都是通过具有角分定位能力的大型单碟望远镜探测到的，而识别其对应体（源或宿主星系）的尝试则依赖于场源的同时变化或奇异场星或星系的存在。这些尝试并没有导致与宿主星系或多波长对应体的明确关联。在这里，我们报告了快速射电暴 FRB 121102 的亚角秒定位，这是唯一已知的重复暴源，使用高时间分辨率的射电干涉观测直接对暴源成像。我们的精确定位表明，FRB 121102 起源于一个微弱的 180 微焦耳连续射电源内的 100 毫角秒范围内，该源的连续谱与非热发射一致，还有一个微弱的（二十五等星）光学对应体。连续射电源的流量密度在天尺度上变化约 10%，甚长基线射电干涉测量得出的角尺寸小于 1.7 毫角秒。我们的观测结果与快速射电暴具有银河系起源或其源位于一个突出的恒星形成星系内的说法不一致。相反，该源似乎与一个低光度活动星系核或一个以前未知的星系际源重合。宿主星系或对应体的定位和识别对于理解其他类型的瞬变事件（包括伽马射线暴和潮汐瓦解事件）的起源和物理机制至关重要。然而，如果其他快速射电暴也有类似的微弱射电和光学对应体，那么我们的发现意味着直接的亚角秒定位可能是提供可靠关联的唯一方法。
