INTEGRAL observes a distant (redshift 2.5) lensed galaxy
The blazar PKS 1830-211 is one of the most distant objects observed so
far by INTEGRAL, it was reported as an ISGRI source in the galactic
centre region. The source is clearly detected in 20-100 keV band. The
image from IBIS/ISGRI is shown in the left panel. Notwithstanding its
high redshift (z=2.507) it is a bright X-ray source, due to
gravitational lensing by an intervening galaxy at z=0.89. Radio
observations show two compact components separated by about 1
arcsecond; this effect (just at the limit of the angular resolution of
Chandra), is clearly visible in the elliptically shaped Chandra images
(central and right panels).
By assuming a magnification factor due to the lensing of the order of
10, the bolometric luminosity of PKS 1830-211 is huge: about 10^48
erg/s! The spectrum can be modelled adding an external source of low
energy photons scattered up to gamma-ray energies by relativistic
electrons. As observed in some high redshift quasars, Chandra spectra
of PKS 1830-211 show evidence of absorption below 5 keV (rest frame).
This effect could be due either to the lens galaxy at z=0.89 or to an
intrinsic warm (ionized) gas at redshift of the source.
Credits: A. De Rosa (IASF Rome), A. Malizia (IASF Bologna)
