Person:

Birkinshaw, Mark

The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first celestial object observed with the Chandra X-Ray Observatory, offering the early surprise of the detection of a remarkable X-ray jet. Several observations with a variety of detector configurations contribute to a total exposure time with the Chandra ACIS of about 100 ks. A spatial analysis of all the available X-ray data, making use of Chandra's spatial resolving power of about 0farcs4, reveals a jet that extends about 10'' to the west of the nucleus. At least four X-ray knots are resolved along the jet, which contains about 5% of the overall X-ray luminosity of the source. Previous observations of PKS 0637-752 in the radio band had identified a kiloparsec-scale radio jet extending to the west of the quasar. The X-ray and radio jets are similar in shape, intensity distribution, and angular structure out to about 9'', after which the X-ray brightness decreases more rapidly and the radio jet turns abruptly to the north. The X-ray luminosity of the total source is log LX ≈ 45.8 ergs s-1 (2-10 keV) and appears not to have changed since it was observed with ASCA in 1996 November. We present the results of fitting a variety of emission models to the observed spectral distribution, comment on the nonexistence of emission lines recently reported in the ASCA observations of PKS 0637-752, and briefly discuss plausible X-ray emission mechanisms.

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 <z< 2), low-frequency-selected (and so unbiased in orientation) 3CRR radio sources are reported. The sample includes 21 quasars (=broad-line radio galaxies) and 17 narrow-line radio galaxies (NLRGs) with matched 178 MHz radio luminosity (log LR(5 GHz) ∼ 44–45). The quasars have high radio core fraction, high X-ray luminosities (log LX ∼ 45–46), and soft X-ray hardness ratios (HR ∼ −0.5) indicating low obscuration. The NLRGs have lower core fraction, lower apparent X-ray luminosities (log LX ∼ 43–45), and mostly hard X-ray hardness ratios (HR > 0) indicating obscuration (NH ∼ 1022–1024 cm−2). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [O iii] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (1022 cm−2 < NH(int) < 1.5 × 1024 cm−2) to CT (NH(int) > 1.5 × 1024 cm−2) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1–0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is ∼60◦ and the obscuring material covers 30◦, ∼12◦ of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10–1000× higher than indicated by their X-ray hardness ratios, and their true LX values are ∼10–100× larger than the hardness-ratio absorption corrections would indicate.