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Evolution of Iron K Alpha Line Emission in the Black Hole Candidate GX 339-4GX 339-4 was regularly monitored with the Rossi X-Ray Timing Explorer during a period (in 1999) when its X-ray flux decreased significantly (from 4.26 x 10(exp -10) to 7.6 x 10(exp -12) ergs in the 3-20 keV band), as the source settled into the 'off state.' Our spectral analysis revealed the presence of a prominent iron K alpha line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at approx. 6.4 keV when the measured flux is above 5 x 10(exp -1) ergs per sq cm/s but is shifted to approx. 6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to a recombination cascade of hydrogen- or helium-like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.
Document ID
20040071152
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Feng, Y. X.
(Alabama Univ. Huntsville, AL, United States)
Zhang, S. N.
(Academia Sinica)
Sun, X.
(Alabama Univ. Huntsville, AL, United States)
Durouchoux, Ph.
(Centre National de la Recherche Scientifique)
Chen, Wan
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Cui, Wei
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 21, 2013
Publication Date
May 1, 2001
Publication Information
Publication: Astrophysical Journal
Volume: 553
Issue: 1
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAG5-7927
Distribution Limits
Public
Copyright
Other

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