We present an X–ray/UV/optical spectrum of the black hole primary in the X–ray nova XTE J1118+480 in quiescence at L _ { x } ~ { } \approx~ { } 4 ~ { } \times~ { } 10 ^ { -9 } L _ { Edd } .
The Chandra , HST 
and MMT spectroscopic observations were performed simultaneously on 2002 January 12 UT .
Because this 4.1-hr binary is located at b = 62 ^ { o } , the transmission of the ISM is very high ( e.g. , 70 % at 0.3 keV ) .
We present many new results for the quiescent state , such as the first far–UV spectrum and evidence for an 0.35 mag orbital modulation in the near–UV flux .
However , the centerpiece of our work is the multiwavelength spectrum of XTE J1118+480 , which we argue represents the canonical spectrum of a stellar–mass black hole radiating at L _ { x } ~ { } \sim~ { } 10 ^ { -8.5 } L _ { Edd } .
This spectrum is comprised of two apparently disjoint components : a hard X–ray spectrum with a photon index \Gamma~ { } = ~ { } 2.02 ~ { } \pm~ { } 0.16 , and an optical/UV continuum that resembles a 13,000 K disk blackbody spectrum punctuated by several strong emission lines .
We present a model of the source in which the accretion flow has two components : ( 1 ) an X–ray–emitting interior region where the flow is advection–dominated , and ( 2 ) a thin , exterior accretion disk with a truncated inner edge ( R _ { tr } ~ { } \sim~ { } 10 ^ { 4 } Schwarzschild radii ) that is responsible for the optical/UV spectrum .
For D~ { } = ~ { } 1.8 kpc , the luminosity of the X–ray component is L _ { x } ~ { } \approx~ { } 3.5 ~ { } \times~ { } 10 ^ { 30 } ergs s ^ { -1 } ( 0.3–7 keV ) ; the bolometric luminosity of the optical/UV component is \approx~ { } 20 times greater .