3C 345 in 1981–86: the spectral energy distribution of the variable component in the infrared and optical regions Free

The relative spectral energy distributions of the variable source in blazar 3C 345 in the IR and optical regions of the spectrum are found from the published multicolour (JHKL and UBVRI) photometric data of 1981–86. Comparison of the data in the B and K bands allows us to combine these into a single spectrum showing that the same variable source is seen in the IR and optical regions. It is found that the spectrum of the variable source is well represented in the whole spectral region from U to L by a homogeneous synchrotron source with α = – 1.39 and ν_c = 6.8 × 10¹⁴ Hz. Even at its lower flux levels, this variable synchrotron source dominates the total observed radiation in the IR.