Extremely Weak Reflection Features in the X-ray Spectrum of XTE J1118+480: Possible Evidence for X-ray-Emitting Jets?

We have simultaneously fit Chandra and RXTE spectra of the Galactic black hole XTE J1118+480 with three models for X-ray reflection. We explored a range of accretion disc ionizations (log(ξ)=1–4; ξ = LX/nR) and iron abundances (0.10–1.00). Our fits with the constant density ionized disc models of Ross & Fabian indicate that≤0.5 per cent (90 per cent confidence upper-limit) of the observed flux is reflected. Fits with the “pexrav” of model Magdziarz & Zdziarski indicate that the two-dimensional solid angle (Ω/2π) subtended by the disc relative to a central source of incident hard X-rays is 0.01 −0.01. A combination of the high inclination (i = 81 degrees), Comptonization, and bulk velocities may each contribute to the low reflection fractions we have measured. The results are also consistent with extended jets being the source of the hard X-ray flux, as the disc would then represent a small solid angle as seen from the emission region.