USA 129: 0.6s early and bright
Below image started some 10 seconds after the flare peak and shows USA 129 still bright, fading from +1 to +2, between Leo's bum and the coma cluster.
SatTrackCam Leiden (Cospar 4353) is an amateur satellite tracking station located at Leiden, the Netherlands. Using a camera it makes accurate positional measurements on satellites of interest, mostly classified satellites -i.e. spy satellites- in order to determine their orbits.