Anticorrelated hard X-ray time lag in GRS 1915+105: evidence for a truncated accretion disk

Abstract

Multiwavelength observations of Galactic black hole candidate sources indicate a close connection between the accretion disk emission and the jet emission. The recent discovery of an anticorrelated time lag between the soft and hard X-rays in Cygnus X-3 (Choudhury & Rao) constrains the geometric picture of the disk-jet connection into a truncated accretion disk, the truncation radius being quite close to the black hole. Here we report the detection of similar anticorrelated time lag in the superluminal jet source GRS 1915+105. We show the existence of pivoting in the X-ray spectrum during the delayed anticorrelation, and we also find that the quasi-periodic oscillation frequency changes along with the spectral pivoting. We explore theoretical models to understand this phenomenon.