Search Publications
Dark Matter Distribution in Galaxy Groups from Combined Strong Lensing and Dynamics Analysis
Crampton, David; Thanjavur, Karun; Willis, Jon
Using a combined analysis of strong lensing and galaxy dynamics, we characterize the mass distributions and the mass-to-light (M/L) ratios of galaxy groups, virialized structures in the mass range of few × 1014 M sun, which form an important transition regime in the hierarchical assembly of mass in ΛCDM cosmology. Our goals a…
Characterizing the Radio-X-ray Connection in GRS 1915+105
Rodriguez, J.; Pooley, G. G.; Prat, L.
We analyzed radio and X-ray observations of GRS 1915+105, between 1995 May and 2006 June, focusing on the times characterized by radio flares and cycles of hard dips—soft spikes in the X-ray light curve. Assuming these flares to be discrete ejections, we applied a plasmon model to the radio data, with good agreement with the light curves. We fitte…
Impact of Coherent Backscattering on the Spectra of Icy Satellites of Saturn and the Implications of Its Effects for Remote Sensing
Buratti, B.; Kolokolova, L.; Tishkovets, V.
We have found systematic variations in the spectra of Saturn's icy satellites Rhea and Iapetus obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS). The main attribute of these variations is a significantly different depth of the absorption bands at different phase angles. We show that these variations likely result from the coh…
A Limit on the Number of Isolated Neutron Stars Detected in the ROSAT All-Sky-Survey Bright Source Catalog
Fox, Derek B.; Rutledge, Robert E.; Turner, Monica L. +2 more
Using new and archival observations made with the Swift satellite and other facilities, we examine 147 X-ray sources selected from the ROSAT All-Sky-Survey Bright Source Catalog (RASS/BSC) to produce a new limit on the number of isolated neutron stars (INSs) in the RASS/BSC, the most constraining such limit to date. Independent of X-ray spectrum a…
Anti-correlated Soft Lags in the Intermediate State of Black Hole Source GX 339-4
Rao, A. R.; Sriram, K.; Choi, C. S.
We report the few hundred second anti-correlated soft lags between soft and hard energy bands in the source GX 339-4 using RXTE observations. In one observation, anti-correlated soft lags were observed using the ISGRI/INTEGRAL hard energy band and the PCA/RXTE soft energy band light curves. The lags were observed when the source was in hard and so…
Discovery of Diffuse Hard X-Ray Emission Around Jupiter with Suzaku
Uchiyama, Y.; Negoro, H.; Miyoshi, Y. +4 more
We report the discovery of diffuse hard (1-5 keV) X-ray emission around Jupiter in a deep 160 ks Suzaku X-ray Imaging Spectrometer data. The emission is distributed over ~16 × 8 Jovian radius and spatially associated with the radiation belts and the Io Plasma Torus (IPT). It shows a flat power-law spectrum with a photon index of 1.4 ± 0.2 with the…
Plasma Near the Heliosheath: Observations and Interpretations
Wang, C.; Richardson, J. D.
Voyager 2 (V2) has observed heliosheath plasma since 2007 August. The plasma flux decreases by 25% before the termination shock (TS), then, as V2 moved into the heliosheath, the plasma density, temperature, and flux all decreased by an additional factor of 2. We suggest three effects combine to cause these decreases. (1) V2 moved into the lower-fl…
Diagnosing Circumstellar Debris Disks
Hahn, Joseph M.
A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting β Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of r…
Statistical Analysis of the very Quiet Sun Magnetism
Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R. +2 more
The behavior of the observed polarization amplitudes with spatial resolution is a strong constraint on the nature and organization of solar magnetic fields below the resolution limit. We study the polarization of the very quiet Sun at different spatial resolutions using ground- and space-based observations. It is shown that 80% of the observed pol…
The Stellar Population and Metallicity Distribution of the Sombrero Galaxy
Spitler, Lee; Mould, Jeremy
Hubble Space Telescope studies of the resolved stellar population of elliptical galaxies have shown that the galaxies form by steady accretion of gas which is all the while forming stars and chemically evolving to a metallicity distribution that is as high as solar composition in the most massive objects that have been analyzed and much lower for …