NASA Scientific and Technical Aerospace Reports

Space Flight Center, Greenbelt, MD, USA, , Huntsville, AL, USA
Evolution of the Iron K-Alpha Emission Line in the Black Hole Candidate GX339-4 During and Outburst Decay Phase
Feng, Y.; Zhang, S.-N.; Chen, W.; Cui, Wei; Bulletin of the American Astronomical Society; December 1999; Volume 31,
pp. 1556; In English; 195th AAS Meeting
Contract(s)/Grant(s): NAG5-7927
Report No.(s): AAS-126.05; Copyright; Avail: Other Sources; Abstract Only
The evolution of the iron K-alpha line emission feature was found from the black hole candidate GX339-4 when its X-ray
flux (2 to 10 keV) decreased significantly. With RXTE observations, a broad line emission feature around 7 keV was detected
in its quiescent and low flux state; while in the high flux state, an emission line feature around 6.4 keV was detected. A similar
6.4 keV line feature was also detected with previous ASCA observations in a high flux state. We consider that the evolution
could be the evidence of the variations in the geometric structure and the physical properties of the accretion flow when the
accretion rate changed. This is because that the 7 keV line feature can be produced by the radiative recombination cascade,
collisional excitation, and fluorescence of Fe XXVI and Fe XXV, which can exist in a very high temperature plasma; while
the 6.4 keV line feature can be produced by fluorescent K-alpha line emission of neutral iron atoms in the cold accretion disk.
(copyright) 1999 American Astronomical Society. All rights reserved.
Author (revised)
K Lines; Iron; Black Holes (Astronomy); X Ray Astronomy
20040073455 California Univ., Berkeley, CA, USA
Modelling the Soft X-Ray and EUV Emission in Classical Novae: EUVE and ROSAT Observations of V1974 Cygni
Stringfellow, Guy S.; Bowyer, Stuart; Astrophysics in the Extreme Ultraviolet; [1996], pp. 401-405; In English
Contract(s)/Grant(s): NAS5-30180; NAG5-3394; Copyright; Avail: Other Sources
We have conducted an extensive analysis of the observability of Classical Novae with the EUVE Lex/B and Al/Ti/C
detectors. Predicted count rates have been computed using optically thin, isothermal plasma models for solar and metal-rich
compositions, and hot ONeMg white dwarf model atmospheres. We find EUVE to be quite sensitive to both the EUV and soft
X-ray emission emitted by the underlying hot white dwarf during novae outbursts, except for the coolest temperatures with
very high intervening hydrogen column density. These results are used to interpret the emission detected during the EUVE
all-sky survey of Nova Cygni 1992 (approx. = V1974 Cyg), 279-290 days after visual maximum. We find the best fit to the
observed emission from V1974 Cyg arises from a hot ONeMg white dwarf with surface temperature approx. 4 x l0(exp 5)
K and a mas of approx. 1.2 solar mass, and derive an interstellar hydrogen column density of approx. 3 x 10(exp 21)/sq cm.
Virtually all this emission arises from supersoft X-rays rather than the EUV. We also report the detection of V1974 Cyg with
the EUVE Deep Survey detector at 549 days after visual maximum. This observation is compatible with the above properties,
indicating that the mechanism responsible for the soft X-ray emission, connected with the underlying white dwarf, had not
yet entirely turned off. We also present analysis of a ROSAT PSPC observation which is contemporaneous with the EUVE
survey observations; this independently confirms the high column density we derived from the EUVE survey observation.
Light curves for the EUVE and ROSAT observations are presented. Statistical tests for variability show that all of these
observations are indeed highly variable over various time scales. The EUVE survey data shows one day variations, the EUVE
DS data show approx. 30 minute fluctuations, while the ROSAT data vary rapidly on time scales of seconds. The EUVE data
shows no periodic variability on any time scale. The implications of the rapid variability are briefly discussed.
Author
X Rays; Models; Extreme Ultraviolet Radiation; Emission; Interstellar Gas
20040073467 Pennsylvania State Univ., University Park, PA, USA
The Flare and Quiescent States of M-dwarf Coronae
Stringfellow, Guy S.; ASP Conference Series; April 22, 2004; Volume 109, pp. 293-294; In English; Cool Stars, Stellar
Systems, and the Sun: 9th Cambridge Workshop
Contract(s)/Grant(s): NAG5-3394; NAG5-2981; Copyright; Avail: Other Sources
As part of an ongoing program searching for and analyzing X-ray variable sources in the ROSAT PSPC archive, the
lightcurves and spectral analysis for two M- dwarf flare stars are presented; AD Leo and VB 8.
Author
Coronas; Dwarf Stars; Flare Stars; Spectrum Analysis; M Stars
20040073502 NASA Marshall Space Flight Center, Huntsville, AL, USA
Effect of Viscosity on the Crystallization of Undercooled Liquids
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