Search Publications
Optical Emission of the Ultraluminous X-Ray Source NGC 5408 X-1: Donor Star or Irradiated Accretion Disk?
Kaaret, P.; Tao, L.; Corbel, S. +3 more
We obtained three epochs of simultaneous Hubble Space Telescope (HST)/Wide Field Camera 3 and Chandra observations of the ultraluminous X-ray source (ULX) NGC 5408 X-1. The counterpart of the X-ray source is seen in all HST filters, from the UV through the near-IR (NIR), and for the first time, we resolve the optical nebula around the ULX. We iden…
Forward Cascade of Whistler Turbulence: Three-dimensional Particle-in-cell Simulations
Gary, S. Peter; Chang, Ouliang; Wang, Joseph
This manuscript describes the first ensemble of three-dimensional (3D) particle-in-cell (PIC) plasma simulations of whistler turbulence. The computational model represents a collisionless, homogeneous, magnetized plasma on which an initial spectrum of relatively long wavelength whistler fluctuations is imposed. The simulations represent a range of…
A Data-driven Model for the Global Coronal Evolution
Wu, S. T.; Feng, Xueshang; Jiang, Chaowei +2 more
This work is devoted to the construction of a data-driven model for the study of the dynamic evolution of the global corona that can respond continuously to the changing of the photospheric magnetic field. The data-driven model consists of a surface flux transport (SFT) model and a global three-dimensional (3D) magnetohydrodynamic (MHD) coronal mo…
Investigating Slim Disk Solutions for HLX-1 in ESO 243-49
Gehrels, N.; Braito, V.; Farrell, S. A. +7 more
The hyperluminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate-mass black hole (BH) candidate, displays spectral transitions similar to those observed in Galactic BH binaries, but with a luminosity 100-1000 times higher. We investigated the X-ray properties of this unique source by fitting multi-epoch data collected…
Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: A Case for Caustic Radio Emission?
Camilo, F.; Gargano, F.; Grove, J. E. +25 more
We report the detection of pulsed gamma-ray emission from the fast millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20 (J1959+2048) using 18 months of survey data recorded by the Fermi Large Area Telescope and timing solutions based on radio observations conducted at the Westerbork and Nançay radio telescopes. In addition, …
X-Ray and Multiwavelength Insights into the Nature of Weak Emission-line Quasars at Low Redshift
Brandt, W. N.; Hall, Patrick B.; Anderson, Scott F. +5 more
We report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z = 0.4-2.5. Our sample was selected from the Plotkin et al. catalog of radio-quiet, weak-featured active galactic nuclei (AGNs). The distribution of relative X-ray brightnes…
Isotopic Ratios in Titan's Methane: Measurements and Modeling
Irwin, P. G. J.; Teanby, N. A.; Flasar, F. M. +10 more
The existence of methane in Titan's atmosphere (~6% level at the surface) presents a unique enigma, as photochemical models predict that the current inventory will be entirely depleted by photochemistry in a timescale of ~20 Myr. In this paper, we examine the clues available from isotopic ratios (12C/13C and D/H) in Titan's m…
The Spectrum of the Recycled PSR J0437-4715 and Its White Dwarf Companion
Pavlov, George G.; Kargaltsev, Oleg; Kaplan, David L. +4 more
We present extensive spectral and photometric observations of the recycled pulsar/white dwarf binary containing PSR J0437-4715, which we analyzed together with archival X-ray and gamma-ray data, to obtain the complete mid-infrared to gamma-ray spectrum. We first fit each part of the spectrum separately, and then the whole multi-wavelength spectrum…
The Magnetic Energy-Helicity Diagram of Solar Active Regions
Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi, Nour-Eddine
Using a recently proposed nonlinear force-free method designed for single-vector magnetograms of solar active regions, we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 162 vector magnetograms corresponding to 42 different active regions. We find a statistically robust, monotonic correlation between the …
Time-resolved Ultraviolet Spectroscopy of the M-dwarf GJ 876 Exoplanetary System
Roberge, Aki; France, Kevin; Linsky, Jeffrey L. +2 more
Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of pl…