The INTEGRAL observatory continues to survey the hard X-ray sky and
will eventually provide an unbiased sample of active galactic nuclei
(AGN), including those whose optical and soft X-ray emission is
obscured by dust and gas. Some of the newly INTEGRAL discovered hard
X-ray sources were observed by CHANDRA, shedding light on their origin
(paper by Sazonov et al. 2005,
astro-ph/0508593).
The images above show two active galaxies that were originally
discovered as hard X-ray sources by INTEGRAL/IBIS (3 arcmin radius
green circles overlayed on CHANDRA/ACIS images). The positions of
bright sources detected by CHANDRA coincide with the cores of the
galaxies (optical image on the right), which tells us that they are
AGNs. Their X-ray spectra show the presence of a high density of
absorbing gas in these AGN, which makes them quite faint at soft X-ray
energies.
Credits: Sazonov et al. (MPA Garching, IKI Moscow)
