Search Publications
Evidence for Elemental Variation in the Ejecta of the TYCHO Supernova Remnant
Hughes, John P.; Gorenstein, P.; Vancura, O.
We present an X-ray study of the Tycho supernova remnant utilizing archival data from the high-resolution imagers (HRIs) on Einstein and ROSAT, the low-energy imaging telescopes (LEITs) on EXOSAT, and spectral data from the Broad Band X-ray Telescope (BBXRT). We have made use of the differing HRI bandpasses to construct images of Tycho in two spec…
Burstlike Events in the Z Source Cygnus X-2
van Paradijs, J.; van der Klis, M.; Kuulkers, E.
We have found nine burstlike events in EXOSAT data of the Z source Cyg X-2. Their durations are of the order of several seconds. Within the limited counting statistics we cannot find an indication for cooling during the burstlike events, which would have indicated that they are bona fide type I bursts, i.e., thermonuclear flashes on the surface of…
Dynamic Processes in Be Star Atmospheres. III. Rapid Multiwavelength Variability in gamma Cassiopeiae
Smith, Myron A.
A review of the characteristics of X-ray emission from gamma Cas suggests various weaknesses with conventional scenarios that invoke Be wind interactions with a putative binary companion. To explore whether this emission might arise instead from sporadic high-energy events on the Be star itself, we have examined the temporal behavior of Voyager 1 …
Emission Spectrum Integrated over an Accretion Disk: Comparison with Observations of Active Galactic Nuclei
Shimura, Toshiya; Takahara, Fumio
Emission spectrum from an accretion disk for active galactic nuclei is obtained by solving the vertical structure and radiative transfer self-consistently and by integrating the local spectrum over radii. We found that even for moderate accretion rates, disks emit a significant portion of the total luminosity in UV through soft X-ray range; for th…
EXOSAT Observations of the Low-Luminosity X-Ray Burster 4U 0614+091: Evidence for a Hard Power-Law Tail
Barret, Didier; Grindlay, Jonathan E.
We have analyzed archival EXOSAT observations of 4U 0614+091 as recorded by the Medium Energy experiment (2-10 keV). The data set consists of five spectra, all associated with low X-ray luminosities (L(X,1-20 keV) ≤ 2 × 1036 ergs s-1, d = 2 kpc). The spectrum corresponding to the highest intensity state (FX
Eclipse Timings of the Low-Mass X-Ray Binary EXO 0748-676: Statistical Arguments against Orbital Period Changes
Wood, Kent S.; Hertz, Paul; Cominsky, Lynn
EXO 0748-676, an eclipsing low-mass X-ray binary, is one of only about four or five low-mass X-ray binaries for which orbital period evolution has been reported. We observed a single eclipse egress with ROSAT . The time of this egress is consistent with the apparent increase in Porb previously reported on the basis of EXOSAT and Ginga o…
Coronal Heating in Flare Stars: Resonant MHD Absorption?
Mullan, D. J.; Johnson, M.
We report on the occurrence of periodicity in X-rays from certain flare stars. Statistically significant periods in the range 70-200 s are present in Einstein data for EQ Vir, Proxima Cen, and AD Leo. Periodicities are also present (although with lower statistical significance) in ROSAT data for AD Leo, and in EXOSAT data for EQ Vir and AD Leo. In…
Determination of Plasma Temperatures and Luminosities Using Multiple Extreme-Ultraviolet and X-Ray Filters
Brown, Alexander; Wood, Brian E.; Linsky, Jeffrey L.
We carefully examine the techniques used to infer temperatures of stellar coronal plasmas from the count rates of several broadband instruments in the X-ray and extreme-ultraviolet spectral ranges. In particular, we determine to what extent temperatures can be constrained and the corresponding uncertainties in the luminosities and emission measure…
Radiation Hydrodynamic Models of Eclipsing Low-Mass X-Ray Binaries
McKee, Christopher F.; Murray, Stephen D.; Woods, D. Tod +2 more
We present the results of self-consistent two-dimensional radiation hydrodynamic models of winds and coronae above accretion disks in low-mass X-ray binaries. The numerical method combines adaptive mesh refinement for the hydrodynamics with combined ray tracking/flux-limited diffusion for the radiation. The results of the models are compared with …