Abstract
We present ASCA SIS and GIS observations of two GHz peaked spectrum (GPS) radio galaxies, PKS 1345+125 (4C12.50, z = 0.122) and 2352+495 (z = 0.237). In the energy band 2–10 keV, 1345+125 is detected with about 2 × 1043 ergs s-1, while 2352+495 is not detected with an upper limit < 7 × 1042 ergs s-1. This is the first reported detection of X-ray emission from a GPS radio galaxy. These measurements do not violate predictions of Heinz et al.'s recent evolving source model for radio sources, although deeper X-ray observations are needed for a strong test of the model. The host galaxy of 1345+125 contains two nuclei separated by 2'' (4 kpc) which are not resolved by the ASCA observations. We suggest that the X-rays are emitted by the western of the two nuclei, which Gilmore & Shaw have shown has a NLRG/Seyfert-2 optical spectrum and which Evans et al. have recently identified with the GPS radio source. We obtain model dependent estimates for the 1345+125 radio source age of about 3 × 104 yr and expansion velocity of approximately 0.02c. We show that in samples of Seyfert 1's and powerful extended radio galaxies, optical emission-line luminosities are of a strength consistent with photoionization by the embedded active galactic nucleus (AGN; estimated using ASCA observations), and 1345+125 fits this picture assuming the X-ray emission is from the western nucleus. In contrast, the extrapolated limits on the nuclear ionizing continuum in 2352+495 are too low to account for the luminosity of the narrow emission-line region. If this is confirmed by further observations, it would favor a model in which some fraction of the emission lines are powered by shocks induced by the radio source or in which some of the AGN photons that ionize the gas are obscured from our view.
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