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Cosmic birefringence is a parity-violating effect that might have rotated theplane of linearly polarized light of the cosmic microwave background (CMB) byan angle $\beta$ since its emission. This has recently been measured to benon-zero at a statistical significance of $3.6\sigma$ in the official PlanckPR4 and 9-year WMAP data. In this work, we constrain $\beta$ using thereprocessed BeyondPlanck LFI and Cosmoglobe DR1 WMAP polarization maps. Thesenovel maps have both lower systematic residuals and a more complete errordescription than the corresponding official products. Foreground $EB$correlations could bias measurements of $\beta$, and while thermal dust $EB$emission has been argued to be statistically non-zero, no evidence forsynchrotron $EB$ power has been reported. Unlike the dust-dominated Planck HFImaps, the majority of the LFI and WMAP polarization maps are instead dominatedby synchrotron emission. Simultaneously constraining $\beta$ and thepolarization miscalibration angle, $\alpha$, of each channel, we find abest-fit value of $\beta=0.35^{\circ}\pm0.70^{\circ}$ with LFI and WMAP dataonly. When including the Planck HFI PR4 maps, but fitting $\beta$ separatelyfor dust-dominated, $\beta_{>70\,\mathrm{GHz}}$, and synchrotron-dominatedchannels, $\beta_{\leq 70\,\mathrm{GHz}}$, we find $\beta_{\leq70\,\mathrm{GHz}}=0.53^{\circ}\pm0.28^\circ$. This differs from zero with astatistical significance of $1.9\sigma$, and the main contribution to thisvalue comes from the LFI 70 GHz channel. While the statistical significances ofthese results are low on their own, the measurement derived from the LFI andWMAP synchrotron-dominated maps agrees with the previously reportedHFI-dominated constraints, despite the very different astrophysical andinstrumental systematics involved in all these experiments.

Cosmoglobe DR1 results. II. Constraints on isotropic cosmic birefringence from reprocessed WMAP and Planck LFI data