Extended Data Fig. 6: High-cadence X-ray observations at earlier times.

a, NICER data obtained between 25 September 2019 and 5 November 2019, close to the time of the optical TDE peak. No variability is detected, with the shaded region showing the range of QPE peaks at late times. Comparing with the observed QPEs at late times suggests that we would have most probably detected about two QPEs if they were active. b, Swift/XRT data²¹ obtained on 13 January 2022, binned in 5-ks fixed bins. The dotted line shows the QPE detected later with XRT. Variability is now observed on approximately hour timescales, but the baseline is insufficient to determine whether this is QPE-like in nature. The error bars show the 1σ uncertainty in count rate.