Person: Worrall, Diana
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Worrall
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Diana
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Worrall, Diana
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Publication Chandra Discovery of a 100 kiloparsec X-Ray Jet in PKS 0637–752(IOP Publishing, 2000) Schwartz, D. A.; Marshall, H. L.; Lovell, J. E. J.; Piner, B. G.; Tingay, S. J.; Birkinshaw, M.; Chartas, G.; Elvis, Martin; Feigelson, E. D.; Ghosh, K. K.; Harris, D. E.; Hirabayashi, H.; Hooper, E. J.; Jauncey, D. L.; Lanzetta, K. M.; Mathur, S.; Preston, R. A.; Tucker, W. H.; Virani, S.; Wilkes, Belinda; Worrall, DianaThe quasar PKS 0637-752, the first celestial X-ray target of the Chandra X-Ray Observatory, has revealed asymmetric X-ray structure extending from 3'' to 12'' west of the quasar, coincident with the inner portion of the jet previously detected in a 4.8 GHz radio image (Tingay et al. 1998). At a redshift of z = 0.651, the jet is the largest (gsim100 kpc in the plane of the sky) and most luminous (~1044.6 ergs s-1) of the few so far detected in X-rays. This Letter presents a high-resolution X-ray image of the jet, from 42 ks of data when PKS 0637-752 was on-axis and ACIS-S was near the optimum focus. For the inner portion of the radio jet, the X-ray morphology closely matches that of new Australian Telescope Compact Array radio images at 4.8 and 8.6 GHz. Observations of the parsec-scale core using the very long baseline interferometry space observatory program mission show structure aligned with the X-ray jet, placing important constraints on the X-ray source models. Hubble Space Telescope images show that there are three small knots coincident with the peak radio and X-ray emission. Two of these are resolved, which we use to estimate the sizes of the X-ray and radio knots. The outer portion of the radio jet and a radio component to the east show no X-ray emission to a limit of about 100 times lower flux. The X-ray emission is difficult to explain with models that successfully account for extranuclear X-ray/radio structures in other active galaxies. We think the most plausible is a synchrotron self-Compton model, but this would imply extreme departures from the conventional minimum energy and/or homogeneity assumptions. We also rule out synchrotron or thermal bremsstrahlung models for the jet X-rays, unless multicomponent or ad hoc geometries are invoked.Publication Revealing the Heavily Obscured Active Galactic Nucleus Population of High-Redshift 3crr Sources With Chandra X-Ray Observations(IOP Publishing, 2013) Wilkes, Belinda; Kuraszkiewicz, Joanna; Haas, Martin; Barthel, Peter; Leipski, Christian; Willner, Steven; Worrall, Diana; Birkinshaw, Mark; Antonucci, Robert; Ashby, Matthew; Chini, Rolf; Fazio, Giovanni; Lawrence, Charles; Ogle, Patrick; Schulz, BernhardChandra observations of a complete, flux-limited sample of 38 high-redshift (1 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.Publication The Chandra X‐Ray Observatory Resolves the X‐Ray Morphology and Spectra of a Jet in PKS 0637-752(IOP Publishing, 2000) Chartas, G.; Worrall, Diana; Birkinshaw, Mark; Cresitello‐Dittmar, M.; Cui, W.; Ghosh, K. K.; Harris, D. E.; Hooper, E. J.; Jauncey, D. L.; Kim, Dong-Woo; Lovell, J.; Mathur, S.; Schwartz, Daniel; Tingay, S. J.; Virani, S. N.; Wilkes, BelindaThe 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.Publication The Einstein database of IPC x-ray observations of optically selected and radio-selected quasars, 1.(IOP Publishing, 1994) Wilkes, Belinda; Tananbaum, Harvey; Worrall, Diana; Avni, Yoram; Oey, M. S.; Flanagan, JoanWe present the first volume of the Einstein quasar database. The database includes estimates of the X-ray count rates, fluxes, and luminosities for 514 quasars and Seyfert 1 galaxies observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory. All were previously known optically selected or radio-selected objects, and most were the targets of the X-ray observations. The X-ray properties of the Active Galactic Nuclei (AGNs) have been derived by reanalyzing the IPC data in a systematic manner to provide a uniform database for general use by the astronomical community. We use the database to extend earlier quasar luminosity studies which were made using only a subset of the currently available data. The database can be accessed on internet via the SAO Einstein on-line system ('Einline') and is available in ASCII format on magnetic tape and DOS diskette.Publication Discovery of a Jetlike Structure at the High-Redshift QSO CXOMP J084128.3+131107(IOP Publishing, 2004) Schwartz, D. A.; Silverman, J.; Birkinshaw, M.; Karovska, Margarita; Aldcroft, Thomas; Barkhouse, W.; Green, P.; Kim, D.-W.; Wilkes, Belinda; Worrall, DianaThe Chandra Multiwavelength Project has discovered a jetlike structure associated with a newly recognized QSO at redshift z = 1.866. The system was 9farcm4 off-axis during an observation of 3C 207. Although significantly distorted by the mirror point-spread function, we use both a ray trace and a nearby bright point source to show that the X-ray image must arise from some combination of point and extended sources, or else from a minimum of three distinct point sources. We favor the former situation, as three unrelated sources would have a small probability of occurring by chance in such a close alignment. We show that interpretation as a jet emitting X-rays via inverse Compton scattering on the cosmic microwave background is plausible. This would be a surprising and unique discovery of a radio-quiet QSO with an X-ray jet, since we have obtained upper limits of 100 μJy on the QSO emission at 8.46 GHz and limits of 200 μJy for emission from the putative jet.Publication Chandra X-Ray Observations of the Redshift 1.53 Radio-Loud Quasar 3c 270.1(IOP Publishing, 2012) Wilkes, Belinda; Lal, Dharam V.; Worrall, Diana; Birkinshaw, Mark; Haas, Martin; Willner, Steven; Antonucci, Robert; Ashby, Matthew; Avara, Mark; Barthel, Peter; Chini, Rolf; Fazio, Giovanni; Hardcastle, Martin; Lawrence, Charles; Leipski, Christian; Ogle, Patrick; Schulz, BernhardChandra X-ray observations of the high redshift (z = 1.532) radio-loud quasar 3C 270.1 in 2008 February show the nucleus to have a power-law spectrum, Γ = 1.66 ± 0.08, typical of a radio-loud quasar, and a marginally detected Fe Kα emission line. The data also reveal extended X-ray emission, about half of which is associated with the radio emission from this source. The southern emission is co-spatial with the radio lobe and peaks at the position of the double radio hot spot. Modeling this hot spot, including Spitzer upper limits, rules out synchrotron emission from a single power-law population of electrons, favoring inverse Compton emission with a field of ∼11 nT, roughly a third of the equipartition value. The northern emission is concentrated close to the location of a 40◦ bend where the radio jet is presumed to encounter an external medium. It can be explained by inverse Compton emission involving cosmic microwave background photons with a field of ∼3 nT, a factor of 7–10 below the equipartition value. The remaining, more diffuse X-ray emission is harder (HR = −0.09 ± 0.22). With only 22.8 ± 5.6 counts, the spectral form cannot be constrained. Assuming thermal emission with a temperature of 4 keV yields an estimate for the luminosity of 1.8×1044 erg s−1, consistent with the luminosity–temperature relation of lower-redshift clusters. However, deeper Chandra X-ray observations are required to delineate the spatial distribution and better constrain the spectrum of the diffuse emission to verify that we have detected X-ray emission from a high-redshift cluster.Publication X-ray spectra of compact extragalactic radio sources(IOP Publishing, 1990) Worrall, Diana; Wilkes, BelindaA comparison is conducted of the 0.1-3.5 keV mean power law energy spectral indices (alpha) measured by the Einstein Observatory IPC for (1) 19 low polarization, flat radio spectrum (FRS) core-dominant QSOs; (2) 12 highly polarized QSOs (HPQs); and (3) 24 radio-selected BL Lac objects. Individual spectral fits are presented for several sources for which results are unavailable elsewhere. A maximum-likelihood analysis was used to ascertain the mean power-law index and the standard deviation for each class, under the assumption of a Gaussian intrinsic distribution. The distributions for HPQ and FRS QSOs are similar, in contrast with a small sample of the X-ray-selected BL Lac objects. Implications of these findings for synchrotron self-Compton models are considered.