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 γ-ray)
dominated by the inverse Compton scattering of the cosmic microwave background.
This gives a consistent spectral index of α=0.88 (Sν∝ν−α) 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 GLAST could separate the γ-ray
emission of 3C 273 from the large scale jet and the small scale jet (i.e. the
core) through measuring the GeV spectrum.Comment: 9 pages, 2 figures, 2 tables, accepted by ChJA