  The softening of a Gamma Ray Burst (GRB) afterglow bears remarkable
similarities to the frequency evolution in a sonic boom. At the front end of
the sonic boom cone, the frequency is infinite, much like a GRB. Inside the
cone, the frequency rapidly decreases to infrasonic ranges and the sound source
appears at two places at the same time, mimicking the double-lobed radio
sources. Although a "luminal" boom violates the Lorentz invariance and is
therefore forbidden, it is tempting to work out the details and compare them
with existing data. This temptation is further enhanced by the observed
superluminality in the celestial objects associated with radio sources and some
GRBs. In this article, we calculate the temporal and spatial variation of
observed frequencies from a hypothetical luminal boom and show remarkable
similarity between our calculations and current observations.
