The spectrum of diffuse cosmic X-rays in the 20-125 keV range

Abstract

Diffuse cosmic X-rays in the energy range 20-125 keV were measured in four balloon flights from Hyderabad, India during 1968-70 using almost identical X-ray telescopes mounted on oriented platforms. The results from these flights show that the spectrum of the diffuse cosmic X-rays can be represented by the form dN/dE=29E ^-2.1±0.3 photons/(cm² sr s keV) in 20-125 keV interval after corrections for photoelectric absorption and Compton scattering effects in the atmosphere. The best fit spectrum of all published results in the energy interval 20-200 keV can be represented by the form dN/dE=36E ^-2.1±0.1 photons/(cm² sr s keV) after similar corrections are effected, and there is no need for a change of spectral index in this energy interval. The intensity at 20 keV obtained from the above spectrum agrees well with that given by the spectral form dN/dE=10E -1.7±0.1 photons/(cm² sr s keV) in the energy interval 1-20 keV in several rocket experiments. Therefore it is concluded that if there is a break in the spectrum, it occurs between 10 and 20 keV with a change of spectral index by about 0.5, or the index is continuously changing from 1.7±0.1 to 2.1± 0.1 in 10-20 keV interval. The implications of the results are briefly discussed.