2016ApJ...823...54P

Most of our knowledge of the radio morphology and kinematics of X-ray binary partially synchrotron self-absorbed compact jets (hereafter, compact jets) is based on the observations of GRS 1915+105, which has the most prominent compact jet. Yet, the compact jet bulk velocity, v, is poorly constrained in the literature, 0.07\lt v/c\lt 0.98 . In spite of this uncertainty, compact jets are often unified with relativistic jets in active galactic nuclei. We estimated v as part of a temporal analysis of GRS 1915+105 jets in "high plateau states" (HPS). We define HPS as a state showing a hard X-ray spectrum and low level of long-term ( \gt 10 s) X-ray activity associated with 15 GHz flux density \gt 70 mJy for \gt 7 consecutive days. The radio emission is associated with compact jet emission. Two HPS were monitored at 15 GHz during their termination with e-folding times of 3.8 and 8.6 hr. We combine this timescale with the scale of the spatial variation of the linear source of a Very Large Baseline Array image preceding the fade of one of these HPS in order to estimate the jet speed. Our assumption that the reduction in radio emissivity propagates as an approximate discontinuity down the HPS jet (leaving a weak jet in its wake) indicates 0.17\lt v/c\lt 0.43 . This agrees closely with the only other existing v estimates that are derived directly from radio images, jet asymmetry produced by Doppler enhancement.