The Spectrum of Diffuse Cosmic Hard X‐Rays Measured withHEAO 1

Open Access
Publisher Website
Google Scholar
Abstract
The spectrum of the diffuse isotropic component of cosmic X-rays over the 13-180 keV range was determined by the UCSD/MIT Hard X-Ray and Gamma-Ray instrument (HEAO 1 A-4) on board the High Energy Astronomical Observatory 1 (HEAO 1). The instrument consists of a complex of actively shielded and collimated scintillation counters, including the low-energy detector set from which the data reported here were obtained. These data join smoothly with the spectrum at lower energies reported by the GSFC HEAO 1 A-2 instrument and with that measured to 400 keV by the HEAO 1 A-4 medium-energy detectors. The HEAO 1 data set also joins the recent results from COMPTEL on the Compton Gamma Ray Observatory (CGRO) in the 1-10 MeV range, which failed to confirm the existence of an "MeV bump" in this range. Although the spectrum over the entire range 3 keV ≤ E ≤ 100 GeV can be fitted by a simple empirical analytic expression, the origin is likely due to a number of distinct source components. The prevailing idea for the origin is that the hard X-ray spectrum is due to X-rays from various active galactic nucleus components, particularly Seyfert galaxies extending to cosmological distances, and that the low-energy gamma rays may be due to emission from Type Ia supernovae, which is also integrated to cosmological distances. The higher energy gamma-ray spectrum defined by EGRET, also on the CGRO, may be due to unresolved gamma-ray-emitting blazars. Models of production by these source components, extrapolated to the present epoch, must reproduce the observationally derived spectrum.
All Related Versions

This publication has 27 references indexed in Scilit: