HIGHLY IONIZED Fe-K ABSORPTION LINE FROM CYGNUS X-1 IN THE HIGH/SOFT STATE OBSERVED WITH SUZAKU

Abstract

We present observations of a transient He-like Fe K α absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start and the end of the episodic accretion phenomena or dips for the first time.We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for ∼10 ks, and weakens thereafter. The overall change in equivalent width is a factor of ∼ 3, peaking at an orbital phase of ∼ 0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe XXV transition, or possibly a mixture of several species less ionized than Fe XXV . The data may be explained by a clump located at a distance of ∼ 10 10−12 cm with a density of ∼ 10 (−13)−(−11) g cm −3 , which accretes onto and/or transits the line-of-sight to the black hole, causing an instant decrease in the observed degree of the ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.

THE REFLECTION COMPONENT FROM CYGNUS X-1 IN THE SOFT STATE MEASURED BYNuSTARANDSUZAKU

“…It is clear that the source was in the soft state with a prominent thermal component and a power-law with a photon index between Γ = 2.59 and 2.67, which meets the Γ > 2.5 criterion for Cyg X-1 to be in the soft state (Grinberg et al 2013). There is clear evidence for absorption due to highly ionized material, which is consistent with the findings of Yamada et al (2013). Also, the fits agree that the ionization state of the disk material that leads to the reflection component is high and that iron is overabundant by a factor of 1.9-2.9 relative to solar.…”

A new possible accretion scenario for ultra-luminous X-ray sources

“…Despite these efforts including ours, none of the ULX analyzed showed noticeable signs of the Fe Kα absorption lines, except for one particular observation of NGC 1313 X-1 (velocity of ∼ 0.2c and EW −61 ± 24 eV; Walton et al 2016). Furthermore, upper limits on the EW of absorption lines, obtained from the other observations of ULXs, are typically several tens eV like in the present case, which is comparable to or more stringent than the actual detections from BHBs in the High/Soft state (20−70 eV; e.g., Ponti et al 2012;Yamada et al 2013). Gathering these results together, the disk winds in ULXs are likely to be generally rather weak or transient.…”

“…On the plane of EW vs N H , figure 8 compares the present ULX sample with representative Galactic NS/BH binaries (Makishima et al 2008;Yamada et al 2013;Sasano 2015). The comparison is limited to High Mass X-ray Binaries (HMBs), i.e., binaries with massive mass-donating stars, because ULXs are generally considered to be similar systems (e.g., Rappaport et al 2005).…”

Long term variability of Cygnus X-1

“…However, dips have still been observed in the soft state with Suzaku (Yamada et al 2013, but we note the strong changes in hardness ratio in their data that may be indicative of spectral evolution during the observation). shows lightcurves and softness ratios of all Chandra observations up to and including ObsID 13219 taken in 2011 February: some weak and short dipping can be seen in the soft state data.…”

“…Boroson & Vrtilek (2010) classified 102 of these observations as hard states and used them to demonstrate the orbital variability of absorption in the hard state, but did not have enough data taken during softer states. At the same time, higher sensitivity snapshots at different φ orb with Chandra (Miller et al 2005;Hanke et al 2009;Miškovičová et al 2015) and Suzaku Miller et al 2012;Yamada et al 2013) revealed a complex structure of the wind with highly Grinberg et al (2013).…”