Evidence for Black Hole Spin in Gx 339-4: Xmm-newton Epic-pn and Rxte Spectroscopy of the Very High State

We have analyzed spectra of the Galactic black hole GX 339−4 obtained through simultaneous 76 ksec XMMNewton/EPIC-pn and 9 ksec RXTE observations during a bright phase of its 2002–2003 outburst. An extremely skewed, relativistic Fe Kα emission line and ionized disk reflection spectrum are revealed in these spectra. Selfconsistent models for the Fe Kα emission line profile and disk reflection spectrum rule-out an inner disk radius compatible with a Schwarzschild black hole at more than the 8σ level of confidence. The best-fit inner disk radius of 2 − 3 rg suggests that GX 339−4 harbors a black hole with a ≥ 0.8 − 0.9 (where rg = GM/c2 and a = cJ/GM2, and assuming that reflection in the plunging region is relatively small). This confirms indications for black hole spin based on a Chandra spectrum obtained later in the outburst. The emission line and reflection spectrum also rule-out a standard power-law disk emissivity in GX 339−4; a broken power-law form with enhanced emissivity inside ∼ 6 rg gives improved fits at more than the 8σ level of confidence. The extreme red wing of the line and steep emissivity require a centrally–concentrated source of hard X-rays which can strongly illuminate the inner disk. Hard X-ray emission from the base of a jet — enhanced by gravitational light bending effects — could create the concentrated hard X-ray emission; this process may be related to magnetic connections between the black hole and the inner disk. We discuss these results within the context of recent results from analyses of XTE J1650−500 and MCG–6–30–15, and models for the inner accretion flow environment around black holes.