Search Publications
High-energy X-ray spectra of Seyferts and Unification schemes for active galactic nuclei
Done, Chris; Middleton, Matthew; Schurch, Nick
The Unified Model of active galactic nuclei (AGN) predicts that the sole difference between type 1 and 2 Seyfert galaxies nuclei is the viewing angle with respect to an obscuring structure around the nucleus. High-energy photons above 20 keV are not affected by this absorption if the column is Compton thin, so their 30-100 keV spectra should be th…
Probing a massive radio galaxy with gravitational lensing
Muxlow, T. W. B.; McKean, J. P.; Koopmans, L. V. E. +3 more
The gravitational lens system CLASS B2108+213 has two lensed images separated by 4.56arcsec. Such a wide image separation suggests that the lens is either a massive galaxy or composed of a group of galaxies. To investigate the structure of the lensing potential we have carried out new high-resolution imaging of the two lensed images at 1.7GHz with…
The Chandra Small Magellanic Cloud Wing Survey - the search for X-ray binaries
Coe, M. J.; McBride, V. A.; McGowan, K. E. +6 more
We have detected 523 sources in a survey of the Small Magellanic Cloud (SMC) Wing with Chandra. By cross-correlating the X-ray data with optical and near-infrared catalogues, we have found 300 matches. Using a technique that combines X-ray colours and X-ray to optical flux ratios, we have been able to assign preliminary classifications to 265 of t…
Wolf-Rayet stars in M33 - II. Optical spectroscopy of emission-line stars in giant HII regions
Drissen, Laurent; Úbeda, Leonardo; Crowther, Paul A. +1 more
We present optical spectra of 14 emission-line stars in M33's giant HII regions NGC 592,595 and 604: five of them are known Wolf-Rayet (WR) stars, for which we present a better quality spectrogram, eight are WR candidates based on narrow-band imagery and one is a serendipitous discovery. Spectroscopy confirms the power of interference filter image…
Luminosity-colour relations for thin-disc main-sequence stars
Cabrera-Lavers, A.; Bilir, S.; Yaz, E. +3 more
In this study we present the absolute magnitude calibrations of thin-disc main-sequence stars in the optical , and in the near-infrared . Thin-disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral …
Exploring the disc/jet interaction in the radio-loud quasar 4C+74.26 with Suzaku
Larsson, J.; Fabian, A. C.; Miniutti, G. +1 more
We report on a 90 ks Suzaku observation of the radio-loud quasar 4C+74.26. The source was observed in its highest flux state to date, and we find that it brightened by about 20 per cent during the observation. We see evidence of spectral hardening as the count rate increases and also find that the rms variability increases with energy up to about …
Evolution in the discs and bulges of group galaxies since z = 0.4
Mulchaey, John S.; Balogh, Michael L.; Oemler, Augustus, Jr. +4 more
We present quantitative morphology measurements of a sample of optically selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and the GIM2D surface brightness fitting software package. The group sample is derived from the Canadian Network for Observational Cosmology Field Galaxy R…
Origin of X-ray emission from transient black hole candidates in quiescence
Yuan, Feng; Zhang, Hui; Cui, Wei +1 more
We report results from a systematic study of X-ray emission from black hole transients in quiescence. In this state, mass accretion is thought to follow the geometry of an outer optically thick, geometrically thin disc and an inner optically thin, geometrically thick radiatively inefficient accretion flow (RIAF). The inner flow is likely also coup…
GD 552: a cataclysmic variable with a brown dwarf companion?
Gänsicke, B. T.; Dhillon, V. S.; Marsh, T. R. +7 more
GD 552 is a high proper motion star with the strong, double-peaked emission lines characteristic of the dwarf nova class of cataclysmic variable (CV) star, and yet no outburst has been detected during the past 12yr of monitoring. We present spectroscopy taken with the aim of detecting emission from the mass donor in this system. We fail to do so a…
Reflection-dominated X-ray spectra of narrow-line Seyfert 1 galaxies: Mrk 478 and EXO 1346.2+2645
Fabian, A. C.; Gallo, L. C.; Zoghbi, A.
Multi-epoch XMM-Newton spectra of the two narrow-line Seyfert 1 (NLS1), Mrk 478 and EXO 1346.2+2645, are presented. The data were fitted with different models, including the relativistically blurred reflection model REFLIONX, which was found to give a good description of both spectra in all epochs. The two sources are reflection dominated with the…