Chandra Grating Spectroscopy of the X-ray Binary 4U 1700-37 in a Flaring State

Authors:
B. Boroson,
S. Vrtilek,
T. Kallman,
M. Corcoran

Comments: 43 pages, 12 figures (4 in color), submitted to The Astrophysical
Journal

Chandra X-ray Observatory grating spectra of the supergiant X-ray Binary 4U
1700-37 reveal emission lines from hydrogen and helium-like S, Si, Mg, and Ne
in the 4-13 A range. The spectrum also shows fluorescent lines from S, Si, and
a prominent Fe K alpha line at 1.94 A. The lines contribute to the previously
unaccounted “soft excess” in the flux in this range at orbital phi~0.7. The
X-ray source was observed during intermittent flaring, and the strengths of the
lines vary with the source state. The widths of the lines (FWHM approximately
1000-2000 km/s) can result from either Compton scattering or Doppler shifts.
Power spectra of the hard X-rays show red noise and the soft X-rays and lines
show in addition quasiperiodic oscillations (QPOs) and a power-spectral break.
Helium-like triplets of Si and Mg suggest that the gas is not in a pure
photoionization equilibrium. We discuss whether resonant scattering could
affect the line ratios or whether a portion of the wind may be heated to
temperatures T~10^6 K.

References and citations for this submission:

SLAC-SPIRES HEP (refers to ,
cited by, arXiv reformatted)