Light curves of the gamma-ray lines at 429 keV (, panel a), 478 keV (, panel b), and511 keV (e⁺ + e⁻→ γ + γ, panel c). Shown are measured flux values in the energy bands 425–433 keV, 475–483 keV, and 506–516 keV, respectively, for 2–3 h time bins (black dots), and ≈ 2-day intervals (red dots), with respect to the optical maximum at T₀ = MJD 57102.67 (vertical dashed line). The zero flux levels are indicated by a horizontal dashed line. No significant excess (> 3σ) is found during the observations. In order to derive an upper limit on the flux from the decay of ⁷Be, an exponential radioactive decay law has been fitted to the data points. As the true time of explosive burning of V5668 is not known, a canonical time offset of Δ t = − 7 d is used. The 3σ upper limit on this decay law is shown as solid blue line in panel b. An upper limit on the annihilation flux at that time is not possible as INTEGRAL was pointed away from the source. See text for more details.