Search Publications
A Strong Correlation between Circumnuclear Dust and Black Hole Accretion in Early-Type Galaxies
Storchi-Bergmann, Thaisa; Simões Lopes, Ramiro D.; de Fátima Saraiva, Maria +1 more
We present a detailed investigation of the incidence of circumnuclear dust structure in a large, well-matched sample of early-type galaxies with and without active galactic nuclei (AGNs). All 34 early-type AGN hosts in our sample have circumnuclear dust, while dust is only observed in 26% (9) of a pair-matched sample of 34 early-type, inactive gal…
Constraints on Neutron Star Properties from X-Ray Observations of Millisecond Pulsars
Bogdanov, Slavko; Grindlay, Jonathan E.; Rybicki, George B.
We present a model of thermal X-ray emission from hot spots on the surface of a rotating compact star with an unmagnetized light-element atmosphere. An application to ROSAT, Chandra, and XMM-Newton X-ray observations of the nearest known rotation-powered millisecond pulsar (MSP) PSR J0437-4715 reveals that the thermal emission from this pulsar is …
Characterization of Gravitational Microlensing Planetary Host Stars
Anderson, Jay; Gaudi, B. Scott; Bennett, David P.
The gravitational microlensing light curves that reveal the presence of extrasolar planets generally yield the planet-star mass ratio and separation in units of the Einstein ring radius. The microlensing method does not require the detection of light from the planetary host star. This allows the detection of planets orbiting very faint stars, but …
Nonthermal Velocities in Solar Active Regions Observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Young, P. R.; Mason, H. E.; Culhane, J. L. +6 more
We discuss nonthermal velocities in an active region as revealed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The velocities are derived from spectral line profiles in the extreme-ultraviolet (EUV) from a strong line of Fe XII at 195.12 Å by fitting each line profile to a Gaussian function. We compare maps of the…
Nuclear Spirals as Feeding Channels to the Supermassive Black Hole: The Case of the Galaxy NGC 6951
Östlin, Göran; Robinson, Andrew; Marconi, Alessandro +5 more
We report the discovery of gas streaming motions along nuclear spiral arms toward the LINER nucleus of the galaxy NGC 6951. The observations, obtained using the GMOS integral field spectrograph on the Gemini North telescope, yielded maps of the flux distributions and gas kinematics in the Hα, [N II] λ6584, and [S II] λλ6717, 6731 emission lines of…
NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region
Peterson, Bradley M.; Pogge, Richard W.; Vestergaard, Marianne +15 more
We describe results from a new ground-based monitoring campaign on NGC 5548, the best-studied reverberation-mapped AGN. We find that it was in the lowest luminosity state yet recorded during a monitoring program, namely L5100=4.7×1042 ergs s-1. We determine a rest-frame time lag between flux variations in the conti…
Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae
Ramirez-Ruiz, Enrico; Kouveliotou, Chryssa; Kaneko, Yuki +8 more
We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evolut…
Source of Nitrogen Isotope Anomaly in HCN in the Atmosphere of Titan
Liang, Mao-Chang; Yung, Yuk L.; Heays, Alan N. +2 more
The 14N/15N ratio for N2 in the atmosphere of Titan was recently measured to be a factor of 2 higher than the corresponding ratio for HCN. Using a one-dimensional photochemical model with transport, we incorporate new isotopic photoabsorption and photodissociation cross sections of N2, computed quantum-m…
Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-Ray Binary Serpens X-1
Strohmayer, Tod E.; Bhattacharyya, Sudip
We report on an analysis of XMM-Newton data from the neutron star low-mass X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data indicates that the previously known broad iron Kα emission line from this source has a significantly skewed structure with a moderately extended red wing. The asymmetric shape of the line is well d…
The Intrinsically X-Ray Weak Quasar PHL 1811. I. X-Ray Observations and Spectral Energy Distribution
Jenkins, Edward B.; Halpern, Jules P.; Leighly, Karen M. +3 more
This is the first of two papers reporting observations and analysis of the unusually bright (mb=14.4), luminous (MB=-25.5), nearby (z=0.192) narrow-line quasar PHL 1811, focusing on the X-ray properties and the spectral energy distribution. Two Chandra observations reveal a weak X-ray source with a steep spectrum. Variability…