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

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 A4) on 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 A2 instrument and with that measured to 400 keV by the HEAO A4 Medium Energy Detectors. The HEAO data set also joins the recent results from COMPTEL on the Compton Gamma-Ray Observatory 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 fit 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 AGN components, particularly Seyfert galaxies extending to cosmological distances, and that the low energy gamma-rays may be due to emission from type 1a Supernovae, 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.

Supermassive black holes in deep multiwavelength surveys

“…Previously, assumed an X-ray background intensity consistent with the Gruber et al (1999) value increased by 40%, which was well fit by a Comptonthick AGN factor of 1 (flat extrapolation of the N H distribution; Fig. 5).…”

“…Figure 8b shows the allowed regions in terms of the Compton-thick AGN factor versus reflection parameter. That is, the shaded regions show the values of these two parameters that produce an integrated X-ray background intensity in the 20-40 keV range, the region most affected by both the number of Compton-thick AGN and R, consistent with: (green region) the Gruber et al (1999) data increased by 40% (the maximum suggested renormalization to match higher estimates with imaging instruments at lower energies; Treister & Urry 2005); (red region) the recent INTEGRAL X-ray background intensity measured using Earth occultation by Churazov et al (2006); (blue region) the original Gruber et al (1999) measurements, not renormalized. In each case uncertainties in the X-ray background intensity were assumed to be 5%.…”

“…The spectrum of Comptonthick AGN at high energies is dominated by the Compton reflection component (e.g., Matt et al 2000), which has a strong peak at E ∼30 keV (Magdziarz & Zdziarski 1995). The observed spectrum of the X-ray background, which we now understand as the integrated emission from previously unresolved AGN, also has peak at about the same energy (Gruber et al 1999). The normalization of the reflection component relative to the direct emission is known only for a few nearby AGN, mostly from BeppoSAX observations (e.g., Perola et al 2002), and therefore this parameter is usually taken as an assumption in AGN population synthesis models that can explain the spectral shape and intensity of the X-ray background.…”

Constraining light dark matter with diffuse X-ray and gamma-ray observations

“…The collected normalized dataset of photon fluxes used to place constraints on decaying and annihilating DM in this paper. Data from HEAO-1 [63] (orange), INTEGRAL [64] (green), COMPTEL [65][66][67] (blue), EGRET [68,69] (red), and Fermi [70] (yellow) are shown. All error bars are statistical, except for the EGRET and Fermi datasets, where the dominant systematic uncertainties are shown.…”

Suzaku observations of iron lines and reflection in AGN

“…For the HXD/PIN, background spectra were extracted from a time-dependent model provided by the instrument team. Cosmic X-ray background (CXB) flux (Gruber et al 1999) was also included in the PIN background model, at a level of 9.0 × 10 −12 erg cm −2 s −1 , integrated over the 15-50 keV band. The HXD/GSO data are only discussed here in the observations of the two brightest AGN in this sample; in MCG -5-23-16 and NGC 2110 the GSO background was extracted from observations of the clusters Abell 1795 and Fornax respectively.…”