Alternative Explanations for Extreme Supersolar Iron Abundances Inferred from the Energy Spectrum of Cygnus X-1

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

来源：Astrophysical Journal, 2018, 855(1): 3.

DOI：10.3847/1538-4357/aaaab1

• accretion, accretion disks
• black hole physics
• stars: individual (Cygnus X-1)
• X-rays: general
• X-rays: stars

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 nonrelativistic 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(-0.9)(+1.6) 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(-0.25)(+0.12)) x 10(20) cm(-3)) impacts other parameters such as the inner radius and inclination of the disk.

• 出版日期2018-3-1