The Mass of the Black Hole in XTE J1118+480

• Published in: arXiv.org 2012-11
• Main Authors: Khargharia, J, Froning, C S, Robinson, E L, Gelino, D M
• Format: Article
• Language: English
• Subjects: Accretion disks; Black holes; Bright spots; Broadband; Dilution; Emission analysis; Expanding universe theory; Flux; Inclination; Infrared photometry; Infrared spectra; Light; Light curve; Near infrared radiation; Parameter estimation; Photometry; Physical properties; X ray binaries; X ray stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1211.2786

We present contemporaneous, broadband, near-infrared spectroscopy (0.9-2.45 micron) and H-band photometry of the black hole X-ray binary, XTE J1118+480. We determined the fractional dilution of the NIR ellipsoidal light curves of the donor star from other emission sources in the system by comparing the absorption features in the spectrum with field stars of known spectral type. We constrained the donor star spectral type to K7 V - M1 V and determined that the donor star contributed 54+/-27% of the H-band flux at the epoch of our observations. This result underscores the conclusion that the donor star cannot be assumed to be the only NIR emission source in quiescent X-ray binaries. The H-band light curve shows a double-humped asymmetric modulation with extra flux at orbital phase 0.75. The light curve was fit with a donor star model light curve, taking into account a constant second flux component based on the dilution analysis. We also fit models that included emission from the donor star, a constant component from the accretion disk, and a phase-variable component from the bright spot where the mass accretion stream impacts the disk. These simple models with reasonable estimates for the component physical parameters can fully account for the observed light curve, including the extra emission at phase 0.75. From our fits, we constrained the binary inclination to 68