Search Publications
On the evidence for narrow, relativistically shifted X-ray lines
Vaughan, S.; Uttley, P.
In recent years, there have been many reported detections of highly redshifted or blueshifted narrow spectral lines (both emission or absorption) in the X-ray spectra of active galaxies, but these are all modest detections in terms of their statistical significance. The aim of this paper is to review the issue of the significance of these detectio…
Keck spectroscopy of the faint dwarf elliptical galaxy population in the Perseus Cluster core: mixed stellar populations and a flat luminosity function
Conselice, Christopher J.; Penny, Samantha J.
We present the result of a photometric and Keck low-resolution imaging spectrometer (LRIS) spectroscopic study of dwarf galaxies in the core of the Perseus Cluster, down to a magnitude of MB = -12.5. Spectra were obtained for 23 dwarf-galaxy candidates, from which we measure radial velocities and stellar population characteristics from …
Multifrequency VLA observations of the FR I radio galaxy 3C 31: morphology, spectrum and magnetic field
Giovannini, G.; Parma, P.; Laing, R. A. +4 more
We present high-quality Very Large Array (VLA) images of the Fanaroff-Riley Class I (FRI) radio galaxy 3C31 in the frequency range 1365-8440MHz with angular resolutions from 0.25 to 40 arcsec. Our new images reveal complex, well resolved filamentary substructure in the radio jets and tails. We also use these images to explore the spectral structur…
MOND plus classical neutrinos are not enough for cluster lensing
Natarajan, Priyamvada; Zhao, Hongsheng
Clusters of galaxies offer a robust test bed for probing the nature of dark matter that is insensitive to the assumption of the gravity theories. Both Modified Newtonian Dynamics (MOND) and General Relativity (GR) would require similar amounts of non-baryonic matter in clusters as MOND boosts the gravity only mildly on cluster scales. Gravitationa…
The nature of the hard state of Cygnus X-3
Larsson, S.; Zdziarski, A. A.; Vilhu, O. +4 more
The X-ray binary Cygnus X-3 (Cyg X-3) is a highly variable X-ray source that displays a wide range of observed spectral states. One of the main states is significantly harder than the others, peaking at ~20 keV, with only a weak low-energy component. Due to the enigmatic nature of this object, hidden inside the strong stellar wind of its Wolf-Raye…
Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy
Östlin, G.; Farrah, D.; Kniazev, A. +16 more
We present near-infrared (NIR) adaptive optics imaging obtained with VLT/NACO and optical spectroscopy from the Southern African Large Telescope of a luminous IR galaxy (LIRG) IRAS 19115-2124. These data are combined with archival Hubble Space Telescope imaging and Spitzer imaging and spectroscopy, allowing us to study this disturbed interacting/m…
Chandra spectroscopy of the hot star βCrucis and the discovery of a pre-main-sequence companion
Miller, Nathan A.; Cohen, David H.; Jensen, Eric L. N. +2 more
In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, βCrucis (βCru B0.5III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near…
The fundamental parameters of the roAp star α Circini
Tuthill, P. G.; Davis, J.; Kurtz, D. W. +12 more
We have used the Sydney University Stellar Interferometer to measure the angular diameter of α Cir. This is the first detailed interferometric study of a rapidly oscillating A (roAp) star, α Cir being the brightest member of its class. We used the new and more accurate Hipparcos parallax to determine the radius to be 1.967 ± 0.066 R⊙. W…
Weighing the black holes in ultraluminous X-ray sources through timing
Belloni, T.; Ponti, G.; Miniutti, G. +3 more
We describe a new method to estimate the mass of black holes in Ultraluminous X-ray Sources (ULXs). The method is based on the recently discovered `variability plane', populated by Galactic stellar-mass black-hole candidates (BHCs) and supermassive active galactic nuclei (AGNs), in the parameter space defined by the black-hole mass, accretion rate…
New Hubble Space Telescope imaging of the counterparts to six ultraluminous X-ray sources
Roberts, T. P.; Levan, A. J.; Goad, M. R.
We report the results of new Hubble Space Telescope imaging of the positions of six ultraluminous X-ray sources (ULXs). Using images in three Advanced Camera for Surveys (ACS) filters, we detect good candidate counterparts to four out of six ULXs, with one more possible detection, and observed magnitudes in the range m ~ 22-26 in the F606W filter.…