Simultaneous HST/ASCA Observations of LMC X-4: X-ray Ionization Effects on a Stellar Wind

Дата и время публикации : 1997-06-17T14:21:41Z

Авторы публикации и институты :
S. D. Vrtilek (Center for Astrophysics)
B. Boroson (Center for Astrophysics)
F. H. Cheng (Villanova University)
R. McCray (JILA)
F. Nagase (ISAS)

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Коментарии к статье: 21 pages, including 5 figures, submitted to the Astrophysical Journal, uses aaspp4.sty, psfig
Первичная категория: astro-ph

Все категории : astro-ph

Краткий обзор статьи: We present first results from simultaneous ultraviolet (UV; HST/GHRS) and X-ray (ASCA) observations of the 13.5s pulsar LMC X-4 taken in 1996 May. The GHRS data are the highest resolution (both temporal and spectral) UV spectra ever taken of LMC X-4. Fits to the UV continuum using a model that incorporates X-ray heating of the companion star and the accretion disk yields a mass accretion rate Mdot=4.0×10^(-8) Msun/yr; the X-ray luminosity implied by this value is consistent with the X-ray flux measured during simultaneous observations. The model accurately predicts observed B magnitude and ultraviolet variations over both orbital and long-term periods. The UV P-Cygni lines show dramatic changes with orbital phase: strong broad absorption near X-ray eclipse and narrow absorption when the X-ray source is in the line-of-sight. We interpret this as a result of X-ray photoionization of the stellar wind; when the neutron star is in front of the normal star, the wind absorption disappears and mainly the photospheric absorption lines are visible. The X-ray pulse period measured during our observations, 13.5090+/-0.0002s, is consistent with steady spin-down over the past 10 years. No pulsations were detected in the UV observations with upper limits to the pulsed fraction around N V and C IV of 1.8% and 2.7% in the continuum and 12.4% and 7% in the absorption troughs.

Category: Physics