Using HEAO 1 A-2 all-sky survey data we have determined the amplitude of intensity fluctuations of the extragalactic 2-10 keV X-ray background (XRB) over an effective solid angle of 1.84 deg2 and their angular correlation function on angular scales of less than 3-degrees (i.e., smaller than the detector's field of view). The observed fluctuations are congruent-to 3 sigma above those expected if the counts keep a Euclidean slope well below the limit of the Piccinotti survey, as indicated by the Einstein Observatory medium sensitivity and deep surveys. A good empirical fit to the data is obtained assuming that the integral counts in the A-2 band have a slope of 1.65(-0.07)+0.06, fully consistent with the best-fit slope of 1.72(-0.10)+0.15 obtained by Piccinotti et al. directly from source counts with the same experiment. Alternatively, the data may imply a significant clustering of extragalactic X-ray sources. However, the non-Poisson constribution of rich clusters of galaxies with clustering radii consistent with optical data (r0 less-than-or-equal-to 50-60 Mpc, H0 = 50) do not fully account for the observed signal. Clustering of AGNs could do the job; the required amplitude of the two-point correlation function depends primarily on the evolution of their luminosity and/or space density and of their clustering properties. The resulting values are consistent with optical data on quasar clustering.
SMALL-SCALE FLUCTUATIONS AND ANGULAR-CORRELATIONS OF THE X-RAY-BACKGROUND IN THE HEAO-1 A-2 ENERGY-BAND - CONSTRAINTS ON CLUSTERING OF X-RAY SOURCES
Danese, Luigi;
1991-01-01
Abstract
Using HEAO 1 A-2 all-sky survey data we have determined the amplitude of intensity fluctuations of the extragalactic 2-10 keV X-ray background (XRB) over an effective solid angle of 1.84 deg2 and their angular correlation function on angular scales of less than 3-degrees (i.e., smaller than the detector's field of view). The observed fluctuations are congruent-to 3 sigma above those expected if the counts keep a Euclidean slope well below the limit of the Piccinotti survey, as indicated by the Einstein Observatory medium sensitivity and deep surveys. A good empirical fit to the data is obtained assuming that the integral counts in the A-2 band have a slope of 1.65(-0.07)+0.06, fully consistent with the best-fit slope of 1.72(-0.10)+0.15 obtained by Piccinotti et al. directly from source counts with the same experiment. Alternatively, the data may imply a significant clustering of extragalactic X-ray sources. However, the non-Poisson constribution of rich clusters of galaxies with clustering radii consistent with optical data (r0 less-than-or-equal-to 50-60 Mpc, H0 = 50) do not fully account for the observed signal. Clustering of AGNs could do the job; the required amplitude of the two-point correlation function depends primarily on the evolution of their luminosity and/or space density and of their clustering properties. The resulting values are consistent with optical data on quasar clustering.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
