Simultaneous Multiwavelength Observations of the Repeating Fast Radio Burst FRB 20190520B with Swift and FAST

Abstract Among several dozen known repeating fast radio bursts, those precisely localized offer the best opportunities to explore their multiwavelength counterparts, which are key to uncovering their origins. Here we report our X-ray, ultraviolet (UV), and optical observations with the Swift satellite of the repeating FRB 20190520B, in coordination with simultaneous radio observations with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our aim was to detect potentially associated multiwavelength bursts and identify any persistent multiwavelength counterparts to the associated persistent radio source (PRS). While a total of 10 radio bursts were detected by FAST during the Swift observations, we detected no X-ray, UV, or optical bursts in accompany with the radio bursts. We obtained the energy upper limits (3 σ ) on any multwavelength bursts as follows: 5.03 × 10 47 erg in the hard X-ray band (15–150 keV), 7.98 × 10 45 erg in the soft X-ray band (0.3–10 keV), and 4.51 × 10 44 erg in the U band (3465 Å), respectively. The energy ratio between soft X-ray (0.3–10 keV) and radio emission of the bursts is constrained as <6 × 10 7 , and the ratio between optical ( U band) and radio as <1.19 × 10 6 . We detect no multiwavelength counterpart to the PRS. The 3 σ luminosity upper limits are 1.04 × 10 47 (15–150 keV), 8.81 × 10 42 (0.3–10 keV), 9.26 × 10 42 (UVW1), and 2.54 × 10 42 erg s −1 ( U ), respectively. We show that the PRS is much more radio-loud than representative pulsar wind nebulae, supernova remnants, extended jets of Galactic X-ray binaries, and ultraluminous X-ray sources, suggestive of boosted radio emission of the PRS.