The local interstellar electron spectrum - Constraints from gamma ray data

The authors present a simple but accurate formulation of the bremsstrahlung emission from cosmic ray electrons in the interstellar medium, simplifying the direct solution of the inverse problem, the calculation of the spectrum corresponding to a given gamma ray emissivity spectrum. Using the emissivity of the local interstellar medium determined in recent COS-B studies, the range of possible electron spectra is derived. The resulting electron spectra are consistent with gamma-ray and radio data only if either (1) the optical depth to radio at 1 MHz is larger than expected, or (2) the electron flux at 1 GeV in the nearby interstellar medium is a factor 2 - 3 times larger than the solar demodulated value given by Rockstroh and Webber (1978).