First order filter cut off frequency
At about 63% of the full peak value, the time = RC (if it were an RC filter): -



This is because: -



And when Tau = t the answer is 0.6321

Half-power frequency: -



That to me looks like it's happening at about 0.8 micro seconds and so,

F = 1000000/(2xPix0.8) = 199 kHz