Search Publications
The Global Implications of the Hard X-Ray Excess in Type 1 Active Galactic Nuclei
Turner, T. J.; Reeves, J. N.; Tatum, M. M. +1 more
Recent evidence for a strong "hard excess" of flux at energies >~ 20 keV in some Suzaku observations of type 1 active galactic nuclei (AGNs) has motivated an exploratory study of the phenomenon in the local type 1 AGN population. We have selected all type 1 AGNs in the Swift Burst Alert Telescope 58 month catalog and cross-correlated them with …
Model-free Multi-probe Lensing Reconstruction of Cluster Mass Profiles
Umetsu, Keiichi
Lens magnification by galaxy clusters induces characteristic spatial variations in the number counts of background sources, amplifying their observed fluxes and expanding the area of sky, the net effect of which, known as magnification bias, depends on the intrinsic faint-end slope of the source luminosity function. The bias is strongly negative f…
HST/ACS Imaging of Omega Centauri: Optical Counterparts of Chandra X-Ray Sources
Anderson, Jay; Cool, Adrienne M.; Haggard, Daryl +5 more
We present results of a search for optical counterparts of X-ray sources in and toward the globular cluster Omega Centauri (NGC 5139) using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The ACS data consist of a mosaic of Wide Field Channel images obtained using F625W, F435W, and F658N filters; with nine pointings we cover t…
Gravitational Conundrum? Dynamical Mass Segregation versus Disruption of Binary Stars in Dense Stellar Systems
Deng, Licai; de Grijs, Richard; Li, Chengyuan +4 more
Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segrega…
Gyrosurfing Acceleration of Ions in Front of Earth's Quasi-parallel Bow Shock
Dandouras, Iannis; Khotyaintsev, Yuri V.; Agapitov, Oleksiy +4 more
It is well known that shocks in space plasmas can accelerate particles to high energies. However, many details of the shock acceleration mechanism are still unknown. A critical element of shock acceleration is the injection problem; i.e., the presence of the so called seed particle population that is needed for the acceleration to work efficiently…
Polarization and Compressibility of Oblique Kinetic Alfvén Waves
Passot, T.; Goldstein, M. L.; Zank, G. P. +3 more
It is well known that a complete description of the solar wind requires a kinetic description and that, particularly at sub-proton scales, kinetic effects cannot be ignored. It is nevertheless usually assumed that at scales significantly larger than the proton gyroscale rL , magnetohydrodynamics or its extensions, such as Hall-MHD and t…
X-Ray Measurement of the Spin-down of Calvera: A Radio- and Gamma-Ray-Quiet Pulsar
Gotthelf, E. V.; Halpern, J. P.; Bogdanov, S.
We measure spin-down of the 59 ms X-ray pulsar Calvera by comparing the XMM-Newton discovery data from 2009 with new Chandra timing observations taken in 2013. Its period derivative is \dot{P}=(3.19+/- \,0.08)\times 10^{-15}, which corresponds to spin-down luminosity \dot{E}=6.1\times 10^{35} erg s-1, characteristic age \tau _c\equiv P/…
The Radial Distribution of Water Ice and Chromophores across Saturn's System
Brown, R. H.; Buratti, B. J.; Clark, R. N. +11 more
Over the past eight years, the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini orbiter has returned hyperspectral images in the 0.35-5.1 µm range of the icy satellites and rings of Saturn. These very different objects show significant variations in surface composition, roughness, and regolith grain size as a result of th…
Hydrogen Chloride in Diffuse Interstellar Clouds along the Line of Sight to W31C (G10.6-0.4)
Godard, B.; Roueff, E.; Lis, D. C. +5 more
We report the detection of hydrogen chloride, HCl, in diffuse molecular clouds on the line of sight toward the star-forming region W31C (G10.6-0.4). The J = 1-0 lines of the two stable HCl isotopologues, H35Cl and H37Cl, are observed using the 1b receiver of the Heterodyne Instrument for the Far-Infrared (HIFI) on board the H…
High-energy Emission from the Composite Supernova Remnant MSH 15-56
Temim, Tea; Slane, Patrick; Plucinsky, Paul P. +3 more
MSH 15-56 (G326.3-1.8) is a composite supernova remnant (SNR) that consists of an SNR shell and a displaced pulsar wind nebula (PWN) in the radio. We present XMM-Newton and Chandra X-ray observations of the remnant that reveal a compact source at the tip of the radio PWN and complex structures that provide evidence for mixing of the supernova (SN)…