Open AccessXMM–Newton and Chandra observations of SHEEP sources
Author(s) -
Georgantopoulos I.,
Nandra K.,
Brotherton M.,
Georgakakis A.,
Papadakis I. E.,
O'Neill P.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10088.x
Subject(s) - physics , astrophysics , rosat , redshift , active galactic nucleus , luminosity , astronomy , population , quasar , line (geometry) , galaxy , demography , geometry , mathematics , sociology
We present Chandra and XMM–Newton observations of 12 bright [ f (2–10 keV) > 10 −13 erg cm −2 s −1 ] sources from the ASCA search for the High Energy Extragalactic Population (SHEEP) survey. Most of these have been either not observed or not detected previously with the ROSAT mission, and therefore they constitute a sample biased towards hard sources. The Chandra observations are important in locating the optical counterpart of the X‐ray sources with accuracy. Optical spectroscopic observations show that our sample is associated with both narrow‐line (NL) (six objects) and broad‐line (BL) active galactic nuclei (AGN) (five objects), with one source remaining unidentified. Our sources cover the redshift range 0.04–1.29, spanning luminosities from 10 42 to 10 45 erg s −1 (2–10 keV). The NL sources have preferentially lower redshift (and luminosity) compared to the BL ones. This can be most easily explained in a model where the NL AGN are intrinsically less luminous than the BL ones in line with the results of Steffen et al. The X‐ray spectral fittings show a roughly equal number of obscured ( N H > 10 22 cm −2 ) and unobscured ( N H < 10 22 cm −2 ) sources. There is a clear tendency for obscured sources to be associated with NL AGN and unobscured sources with BL ones. However, there is a marked exception with the highest obscuring column observed at a BL AGN at a redshift of z = 0.5.