We present the results of a detailed spectral analysis of optically faint hard X-ray sources in the Chandra deep fields selected on the basis of their high X-ray to optical flux ratio (X/O). The stacked spectra of high X/O sources in both Chandra deep fields, fitted with a single power-law model, are much harder than the spectrum of the X-ray background (XRB). The average slope is also insensitive to the 2-8 keV flux, being approximately constant around Γ~= 1 over more than two decades, strongly indicating that high X/O sources represent the most obscured component of the XRB. For about half of the sample, a redshift estimate (in most of the cases a photometric redshift) is available from the literature. Individual fits of a few of the brightest objects and of stacked spectra in different redshift bins imply column densities in the range 10<SUP>22</SUP>-10<SUP>23.5</SUP> cm<SUP>-2</SUP>. A trend of increasing absorption towards higher redshifts is suggested.

X-ray spectral analysis of optically faint sources in the Chandra deep fields / F. Civano;A. Comastri;M. Brusa. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - STAMPA. - 358:(2005), pp. 693-704.

X-ray spectral analysis of optically faint sources in the Chandra deep fields

BRUSA, MARCELLA
2005

Abstract

We present the results of a detailed spectral analysis of optically faint hard X-ray sources in the Chandra deep fields selected on the basis of their high X-ray to optical flux ratio (X/O). The stacked spectra of high X/O sources in both Chandra deep fields, fitted with a single power-law model, are much harder than the spectrum of the X-ray background (XRB). The average slope is also insensitive to the 2-8 keV flux, being approximately constant around Γ~= 1 over more than two decades, strongly indicating that high X/O sources represent the most obscured component of the XRB. For about half of the sample, a redshift estimate (in most of the cases a photometric redshift) is available from the literature. Individual fits of a few of the brightest objects and of stacked spectra in different redshift bins imply column densities in the range 1022-1023.5 cm-2. A trend of increasing absorption towards higher redshifts is suggested.
2005
X-ray spectral analysis of optically faint sources in the Chandra deep fields / F. Civano;A. Comastri;M. Brusa. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - STAMPA. - 358:(2005), pp. 693-704.
F. Civano;A. Comastri;M. Brusa
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/143118
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