The transient sky is rich with a variety of phenomena that change in location and/or luminosity over timescales from milli-seconds to months. And our knowledge of the transient sky will only continue to improve and diversify with the onset of new facilities such as the Vera C. Rubin Observatory, which released its first images last week. One of the most enigmatic classes of transients are fast radio bursts (FRBs): bright, millisecond-duration pulses of radio emission generally detected at frequencies between 0.4 and 1.5 GHz. Though the first FRB was reported in 2007, the first FRB host galaxy was not confidently established until 2017, confirming that most FRBs are of extragalactic origin. Some repeating FRB sources have been seen to produce several to hundreds of bursts, while the majority of sources are associated with only one FRB detection.  Despite almost 1000 published FRB detections to date, including ∼100 with confident host associations, FRB progenitors and their emission mechanisms are still not well understood.

Muller et al. present Very Large Telescope (VLT)/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by ASKAP. They focus on the faint host of FRB 20230708A, identified at low redshift, z=0.105. This indicates an intrinsically very low-luminosity galaxy, making it the lowest-luminosity non-repeating FRB host to date by a factor of ∼3, and slightly dimmer than the lowest-luminosity host for repeating FRBs. Its discovery demonstrates that FRBs can arise in among the faintest, metal-poor galaxies of the universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high-z universe where young, low-mass galaxies proliferate. The image above shows the VLT/FORS2 R-band image of the host galaxy
associated with FRB 20230708A (at the center of the image). The VLT/X-Shooter slit outline is shown in white, and the FRB localization ellipse is shown in black.