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A cosmic-ray explanation of the galactic ridge of cosmic X-rays

Abstract

Recent observations1 with the Exosat X-ray satellite have confirmed the existence of an apparently diffuse galactic ridge of emission extending over the inner Galaxy (l = 320° −40°) and confined to about ±2° in galactic latitude. On the basis of measurements2 carried out in the galactic plane at l55°, we have proposed previously3 that the diffuse galactic X-ray flux known at that time could be understood in terms of the synchrotron radiation of cosmic-ray electrons in the galactic magnetic field. The more extensive Exosat measurements fit nicely into this picture and the X-ray-producing electrons can now be readily understood as being secondary to the ultra-high-energy protons, which are themselves generated in galactic objects as epitomized by the recently discovered4,5 Cygnus X-3. We show here that, on this model, the number of Cyg X-3-like objects present in the Galaxy at any one time, averaged over the past 103 yr or so, is 30.

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Bhat, C., Kifune, T. & Wolfendale, A. A cosmic-ray explanation of the galactic ridge of cosmic X-rays. Nature 318, 267–269 (1985). https://doi.org/10.1038/318267a0

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