A redshift for the host galaxy of the repeating FRB20251130A
ATel #17619; A. C. Gordon, W. Fong (Northwestern University), M. Caleb (University of Sydney), I. Pastor-Marazuela (ASTRON), K. Shaji (University of Sydney), B. W. Stappers (University of Manchester), Mayuresh Surnis (IISER Bhopal), J. Tian (University of Manchester), Fabian Jankowski (Paris Observatory | PSL) on behalf of the MeerTRAP and Fast and Fortunate for FRB Follow-up (F4) Collaborations
on 21 Jan 2026; 18:26 UT
Credential Certification: Alexa Gordon (alexagordon2026@u.northwestern.edu)
Subjects: Optical, Transient, Fast Radio Burst
We report on the spectroscopic redshift of the host galaxy of the repeating FRB20251130A. This FRB was discovered by the MeerTRAP Collaboration and localized to sub-arcsecond precision to its host galaxy with a 99.48% probability of association (ATel #17548).
On 8 January and 13 January 2026 UT, we obtained optical spectroscopy of the FRB20251130A host with the Goodman High Throughput Spectrograph Red Camera on the 4m Southern Astrophysical Research Telescope (Program SOAR2025B-031, PI: Gordon). In 4x900s exposures we detect [OII] 3727, [OIII] 4959,5007, and H-beta in emission at a common redshift of z = 0.4191+/-0.0003. This value is in agreement with the photometric redshift estimate from the DESI Legacy Survey DR10 source catalog (Dey et al. 2019) of 0.41 +0.12/-0.10 (95% confidence) as stated in ATel #17548.
At this redshift, the angular offset of the FRB to its host center of ~0.91 arcsec (ATel #17548) translates to a physical offset of ~5.1 kpc; this is consistent with, though slightly larger than, the median physical offset of the FRB host population (Gordon et al. 2025). We infer a host optical luminosity of 7.1 x 10^43 erg/s which is among the brightest of known repeaters (Gordon et al. 2023).
ATel #17548 reported four bursts at an average dispersion measure (DM) of 977 pc/cm^3. This sightline has a DM MW ISM contribution of ~60 pc/cm^3 (YWM16 model, ATel #17548), and we assume a DM MW halo contribution of 40 pc/cm^3. At this redshift, the DM cosmic contribution is estimated to be 357 +441/-128 pc/cm^3 (95% confidence; Connor et al. 2025). Thus, the DM budget of this FRB leaves a remainder of 520 +128/-441 pc/cm^3 along the sightline. This is larger than the median DM host of 186 pc/cm^3 (James et al. 2022c), suggesting either an elevated DM host and/or additional contributions from intervening halos along the FRB sightline.
We thank the SOAR Observatory staff for scheduling and executing these observations.
