The High-Energy Spectra of Accreting Black Holes: Viewing the Matter as It Disappears Down the Schwarzschild Drain

Abstract

Many attempts to demonstrate the existence of black holes have proven difficult, largely because the very defining property of black holes prevents any outward propagation of radiation. Dynamical studies of binaries have led to convincing stellar-mass s BHCs (Orosz & Bailyn, 1997), and kinematic studies from water masers in several active galactic nuclei (Miyoshi et al. 1995) are strongly suggestive, but it is desirable to identify a generic signature with a broader range of applicability. Recent efforts to interpret asymmetric line profiles in terms of gravitational redshift effects within a few Schwarzschild radii of the black hole have attracted considerable attention (Bromley, Miller & Pariev, 1998). These efforts however, neglect some important effects, which may invalidate the conclusions. The fundamental signature of accreting black holes should be direct observation of the matter “drain” (Titarchuk, Mastchiadis & Kylafis 1997, Titarchuk & Zannias, 1998) — that is to observe the matter as it flows inward with velocities approaching the speed of light near the event horizon. We have shown (Titarchuk & Zannias, 1998) that the behavior of the matter flowing down this “drain” is linked to the very nature of the black hole itself and that a distinct observational signature is produced. Here we present the observational data that demonstrate the existence of black holes in the five binary systems GRO J1655–40, GRS 1915+105, GRS 1739–278, 4U 1630–47 and XTE J 1755–32.