Thermonuclear X-ray bursts from 4U 1636 − 536 observed with<i>AstroSat</i>

We report results obtained from the study of 12 thermonuclear X-ray bursts in 6 AstroSat observations a neutron star binary and well-known burster, 4U 1636$-$536. Burst oscillations at $\sim$581 Hz are observed with 4$-$5$\sigma$ confidence three these bursts. The rising phase burst show decreasing trend fractional rms amplitude 3$\sigma$ confidence,by far strongest evidence flame spreading AstroSat. During initial 0.25 second rise very high value (34.0$\pm$6.7%) is observed. concave shape profile provides strong latitude-dependent speeds, possibly due to effects Coriolis force. observe decay amplitudes comparable that during phase, plausibly combined effect both surface modes as well cooling wake. Doppler shifts rapid rotation might cause hard pulses precede soft pulses, resulting lag. distance source estimated using PRE consistent known $\sim$6 kpc.