We present a modified stratified jet model to interpret the observed spectral energy distributions of knots in 3C 273 jet .
Based on the hypothesis of the single index of the particle energy spectrum at injection and identical emission processes among all the knots , the observed difference of spectral shape among different 3C273 knots can be understood as a manifestation of deviation of the equivalent Doppler factor of stratified emission regions in individual knot from a characteristic one .
The summed spectral energy distribution of all the ten knots in 3C 273 jet can be well fitted by two components , low-energy ( radio to optical ) component dominated by the synchrotron radiation and high-energy component ( UV , X-ray and \gamma -ray ) dominated by the inverse Compton scattering of the cosmic microwave background .
This gives a consistent spectral index of \alpha = 0.88 ( S _ { \nu } \propto \nu ^ { - \alpha } ) and a characteristic Doppler factor of 7.4 .
Assuming the average of the summed spectrum as the characteristic spectrum of each knot in the 3C273 jet , we further get a distribution of Doppler factor .
We discuss the possible implications of these results for the physical properties in 3C 273 jet .
Future GeV observations with \it GLAST could separate the \gamma -ray emission of 3C 273 from the large scale jet and the small scale jet ( i.e .
the core ) through measuring the GeV spectrum .