Spectral Ages of Giant Radio Sources
  Multifrequency observations with the GMRT and the VLA are used to determine
the spectral breaks in consecutive strips along the lobes of a sample of
selected giant radio sources (GRSs) in order to estimate their spectral ages.
The maximum spectral ages estimated for the detected radio emission in the
lobes of our sample of ten sources has a median value of $\sim$20 Myr. The
spectral ages of these GRSs are significantly older than smaller sources. In
all but one source (J1313+6937) the spectral age gradually increases with
distance from the hotspot regions, confirming that acceleration of the
particles mainly occurs in the hotspots. Most of the GRSs do not exhibit zero
spectral ages in the hotspots. This is likely to be largely due to
contamination by more extended emission due to relatively modest resolutions.
The injection spectral indices range from $\sim$0.55 to 0.88 with a median
value of $\sim$0.6. We show that the injection spectral index appears to be
correlated with luminosity and/or redshift as well as with linear size.
