3 years ago

Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1.

Maica Clavel, Jeng-Lun Chiu, Victoria Grinberg, Dominic J. Walton, Poshak Gandhi, Didier Barret, Katja Pottschmidt, Javier A. Garcia, Michael L. Parker, Felix Furst, Andrew Fabian, John A. Tomsick, Kazutaka Yamaoka, Jon M. Miller

Here we study a 1-200 keV energy spectrum of the black hole binary Cygnus X-1 taken with NuSTAR and Suzaku. This is the first report of a NuSTAR observation of Cyg X-1 in the intermediate state, and the observation was taken during the part of the binary orbit where absorption due to the companion's stellar wind is minimal. The spectrum includes a multi-temperature thermal disk component, a cutoff power-law component, and relativistic and non-relativistic reflection components. Our initial fits with publicly available constant density reflection models (relxill and reflionx) lead to extremely high iron abundances (>9.96 and 10.6(+1.6)(-0.9) times solar, respectively). Although supersolar iron abundances have been reported previously for Cyg X-1, our measurements are much higher and such variability is almost certainly unphysical. Using a new version of reflionx that we modified to make the electron density a free parameter, we obtain better fits to the spectrum even with solar iron abundances. We report on how the higher density (n_e = (3.98(+0.12)(-0.25))E20 cm-3) impacts other parameters such as the inner radius and inclination of the disk.

Publisher URL: http://arxiv.org/abs/1801.07267

DOI: arXiv:1801.07267v1

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