The resonant inverse Compton scattering spectrum of an assembly of relativistic electrons in a varying magnetic field

Resonant inverse Compton scattering (RICS) of relativistic electrons in intense magnetic fields is an effective mechanism for producing gamma rays. On the basis of our preceding work, we derive the fundamental formula of the radiative spectrum of the collective RICS produced by a large assembly of relativistic electrons with a power-law energy spectrum moving outward along the magnetic axis of the neutron star. Then we obtain some simple analytical expressions for the collective RICS radiation in several typical low-frequency radiation fields (e.g., thermal Bremsstrahlung, black-body radiation and non-thermal low-frequency radiation with power-law spectrum). These will be convenient for comparison with actually observed spectral shapes. As shown by the computation, when the matching condition (i.e., condition of approximate resonance) is satisfied, the radiative efficiency of RICS is very high and all its spectral shapes are broken power-law with two-segments, irrespective of the properties of the ambient low-frequency field. The calculations once again verified that the RICS is an ideal and highly efficient mechanism for gamma-ray pulsars and gamma-ray bursts (GRBs) in the region of high-energy rays (i.e., hard X-rays and gamma-rays).