Short pulses of microwave radiation are emitted fromthe Crab nebula at a distance
L from the earth. When they reach the earth, the frequencycomponents of the pulses
are dispersed after a travel time T, such that waves of differentfrequencies arrive at
different times. The observed dispersion is due to the interveninginterstellar plasma,
which enables us to estimate the electron density of this plasma.Assuming one knows L
by other means, obtain the expression for the electron density.Assume v p ≈ vg which is
a reasonable approximation for interstellar medium.
