2008/05/28 by A. Georgakakis, K. Nandra, E. S. Laird +2 · 154 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Magnitude (astronomy) #Point source #Population #Range (aeronautics) #Sample (material) #Sensitivity (control systems) #Source counts #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2008.13423.x
published in Monthly Notices of the Royal Astronomical Society 388(3), 1205-1213 (Oxford University Press) · Accepted for publication in MNRAS. Data products available at http://astro.imperial.ac.uk/research/xray/
arxiv created 2008/05/28 · openalex publication_date 2008/07/09 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a new method for determining the sensitivity of X-ray imaging observations, which correctly accounts for the observational biases that affect the probability of detecting a source of a given X-ray flux, without the need to perform a large number of time-consuming simulations. We use this new technique to estimate the X-ray source counts in different spectral bands (0.5–2, 0.5–10, 2–10 and 5–10 keV) by combining deep pencil-beam and shallow wide-area Chandra observations. The sample has a total of 6295 unique sources over an area of 11.8 deg2 and is the largest used to date to determine the X-ray number counts. We determine, for the first time, the break flux in the 5–10 keV band, in the case of a double power-law source count distribution. We also find an upturn in the 0.5–2 keV counts at fluxes below about 6 × 10−17erg s−1cm−2. We show that this can be explained by the emergence of normal star-forming galaxies which dominate the X-ray population at faint fluxes. The fraction of the diffuse X-ray background resolved into point sources at different spectral bands is also estimated. It is argued that a single population of Compton thick active galactic nuclei (AGN) cannot be responsible for the entire unresolved X-ray background in the energy range 2–10 keV.