The Inclination Angle and Mass of the Black Hole in XTE J1118+480

Abstract

We have obtained optical and infrared photometry of the quiescent soft Xray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H-and K s -band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with a K7V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68 • ± 2 • . This inclination angle corresponds to a primary black hole mass of 8.53±0.60 M ⊙ . Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72±0.10 kpc to XTE J1118+480.

Constraints on relativistic jets in quiescent black hole X-ray binaries from broad-band spectral modelling

“…The differences in the flux densities within each filter are consistent with the expected degree of periodic variability due to orbital modulations of the secondary star. To incorporate this systematic into the broadband spectral fitting, we use the average flux density for each of the six filters over both nights (after correcting for Galactic extinction), and then we add systematic error bars to each of the six data points at the ±15% level (the amplitude of the orbital modulations are typically ±0.15-0.20 mag; Gelino et al 2006). …”

“…For the Chandra observation, we report the absorbed flux from 0.3-7 keV in erg s −1 cm −2 , and the quoted uncertainty is at the 90% confidence level (all other error bars are ±1σ). c The extinction in each filter is calculated assuming A V = 0.065 mag (Gelino et al 2006) and a Cardelli, Clayton & Mathis (1989) reddening law with R V = 3.1. For the Swift/UVOT filters, we estimate the extinction using the A λ /A V ratios tabulated in Kataoka et al (2008).…”

“…To this aim, we recently obtained new coordinated Chandra X-ray, SWIFT ultraviolet (UV), William Herschel Telescope optical and NIR, and Karl G. Jansky Very Large Array (VLA) radio observations of the BHXB XTE J1118+480 (hereafter J1118). Given its nearby and well-constrained distance of 1.72 ± 0.10 kpc (Gelino et al 2006) and high Galactic latitude (b = +62 • ; meaning that the amount of line of sight absorption is small), J1118 is one of the few known BHXBs for which it is possible to simultaneously detect both radio and X-ray emission in quiescence. Indeed, our new VLA observation yielded the lowest-luminosity radio detection of a BHXB jet to date (Gallo et al 2014).…”

“…Results from our best model-fit are presented in Section 4, which are then discussed in Section 5. Throughout, we adopt the following parameters for J1118: black hole mass MBH = 7.5 M ⊙ , orbital inclination i = 68 • (Khargharia et al 2013), and distance d = 1.72 ± 0.10 kpc (Gelino et al 2006). The orbital period is P orb = 4.08(±5 × 10 −6 ) h (Torres et al 2004).…”

A leptonic/hadronic jet model for the low-mass microquasar XTE J1118+480

“…The source XTE J1118+480 is an X-ray binary located at a distance of ∼ 1.7 kpc (Gelino et al 2006) at high galactic latitudes (b = +62.3 • ). The mass of compact object is larger than 6M (McClintock et al 2000) being, therefore, a firm black hole candidate in the galactic halo.…”