Fast radio bursts (FRBs) emit broadband radio emission that may, in rare cases, encode atomic hydrogen (HI) absorption signals as they traverse the interstellar medium of their host galaxies. Though considered in the early FRB literature, the demanding observational prerequisites and the rarity of suitable events have meant that no thorough search for HI absorption in FRB spectra has yet been undertaken. Here, we present an updated systematic analysis assessing the likelihood of modern facilities to detect such absorption features. As a proof of concept, we search for absorption in the spectrum of the bright ASKAP-localised FRB 20211127I, finding a $3σ$ opacity upper limit of 0.51. While this test case offers little constraining power, we find that narrow FRBs with fluences exceeding 20/70/150 Jy ms observed with MeerKAT/ASKAP/DSA can probe opacities below 0.1 - a regime in which absorption detections become physically meaningful. We further highlight that stacking thousands of bursts from hyperactive repeaters with FAST offers a very powerful avenue toward detection. Finally, we discuss the broad scientific potential of such detections, including constraints on extragalactic HI spin temperatures, a means to physically probe the environment surrounding the progenitor, and a path towards disentangling host galaxy contributions to dispersion and scattering.
The Low-mass Dwarf Host Galaxy of Nonrepeating FRB 20230708A
Maria Mitchell Observatory（玛丽亚·米切尔天文台）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；University of Glasgow（格拉斯哥大学）；Northwestern University（西北大学）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)（天体物理学跨学科探索与研究中心）；Macquarie University（麦考瑞大学）；University of California, Santa Cruz（加利福尼亚大学圣克鲁兹分校）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)（卡弗里宇宙物理学和数学研究所）
Fast Radio Bursts in the Era of the Vera C. Rubin Observatory's Legacy Survey of Space and Time
International Centre for Radio Astronomy Research, Curtin University（国际无线电天文研究中心，科廷大学）；Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS)（南里奥格兰德联邦大学物理研究所）；Australia Telescope National Facility, CSIRO Space & Astronomy（澳大利亚望远镜国家设施，CSIRO空间与天文学部）；Sydney Institute for Astronomy, School of Physics, The University of Sydney（悉尼大学物理学院悉尼天体物理研究所）；Department of Physics, University of Washington（华盛顿大学物理系）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理学与超级计算中心）；Kavli IPMU (WPI), UTIAS, The University of Tokyo（东京大学宇宙起源研究核心理论中心（ Kavli IPMU））；School of Mathematical and Physical Sciences, Macquarie University（麦考瑞大学数理科学学院）；Department of Physics, University of Oxford（牛津大学物理系）
McGill University（麦吉尔大学）；Massachusetts Institute of Technology（麻省理工学院）；West Virginia University（西弗吉尼亚大学）；Carnegie Mellon University（卡内基梅隆大学）；National Centre for Radio Astrophysics（国家射电天体物理中心）；National Research Council of Canada（加拿大国家研究委员会）
