Radio variability of J1544 compared to its relatively stable X-ray flux over the years. This figure extends Fig. 1 from Jaodand et al. (2021b) by incorporating observations from Gusinskaia et al. (2025) and this work. Top panel: Unabsorbed X-ray flux in the 1–10 keV range (estimated using the entire observations, including both high and low modes) from Jaodand et al. (2021b) (dark blue squares), Gusinskaia et al. (2025) (light blue hexagons), and this work (green point). For consistency, we extracted the flux in the 1–10 keV band from our XMM-Newton observation, obtaining F_X = (2.79 ± 0.04)×10⁻¹² erg cm⁻² s⁻¹, by following the procedure detailed in Sect. 3.1. The low X-ray flux around MJD 57179 is likely due to the source remaining in the X-ray low mode throughout this short (418 s) observation, as noted by Jaodand et al. (2021b). Bottom panel: VLA radio flux density in the X band (8–12 GHz) from Jaodand et al. (2021b) (dark red squares are for detections and downward triangles are for 3σ upper limits) and from Gusinskaia et al. (2025) at 8–12 GHz (X band) around 58224 MJD (red hexagon) and at 4–8 GHz (C band) around 58491 MJD (orange hexagon). The 3σ upper limit of ∼9 μJy at 4–8 GHz (C band) from this work is indicated by the brown downward triangle. For consistency with Jaodand et al. (2021b), the plot shows the radio flux density from Gusinskaia et al. (2025) and the upper limit derived in this work both extracted using the entire VLA observation, rather than restricting to intervals simultaneous with X-ray low modes. The dashed vertical lines mark the epochs of X-ray observations for reference.