Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2009-01-14
Astrophys.J.695:888-899,2009
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
12 pages, 20 figures, accepted for publication in ApJ
Scientific paper
10.1088/0004-637X/695/2/888
We present the results from simultaneous Chandra HETGS and RXTE observations of the microquasar GRS 1915+105 in its quasi-stable "soft state" (or State A) performed on 2007 August 14, several days after the state transition from "hard state" (State C). The X-ray flux increased with spectral hardening around the middle of the Chandra observation, after which the 67 Hz QPO became significant. The HETGS spectra reveal at least 32 narrow absorption lines from highly ionized ions including Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, whose features are the deepest among those ever observed with Chandra from this source. We find that the absorber has outflow velocities of ~150 and ~500 km s^{-1} with a line-of-sight velocity dispersion of ~70 and ~200 km s^{-1} for the Si XIV and Fe XXVI ions, respectively. The larger velocity and its dispersion in heavier ions indicate that the wind has a non-uniform dynamical structure along the line-of-sight. The location of the absorber is estimated at ~(1-3)x10^5 r_g (r_g is the gravitational radius) from the source, consistent with thermally and/or radiation driven winds. The continuum spectra obtained with RXTE in the 3-25 keV band can be well described with a thermal Comptonization with an electron temperature of ~4 keV and an optical depth of ~5 from seed photons from the standard disk extending down to (4-7) r_g. In this interpretation, most of the radiation energy is produced in the Comptonization corona, which completely covers the inner part of the disk. A broad (1\sigma width of ~0.2 keV) iron-K emission line and a smeared edge feature are detected, which can be explained by reflection from the accretion disk at radii larger than 400 r_g.
Remillard Ronald
Ueda Yoshihiro
Yamaoka Kazutaka
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