Au-scale synchrotron jets and superluminal ejecta in GRS 1915+105

Radio imaging of the microquasar GRS 1915+105 with the Very Long Baseline Array (VLBA) over a range of wavelengths (13, 3.6, 2.0, and 0.7 cm), in different states of the black hole binary, always resolves the nucleus as a compact jet of length similar to 10 lambda (cm),, AU. The nucleus is best imaged at the shorter wavelengths, on scales of 2.5-7 AU (0.2-0.6 mas resolution). The brightness temperature of the core is T-B greater than or equal to 10(9) K, and its properties are better fitted by a conically expanding synchrotron jet model rather than a thermal jet. The nuclear jet varies in similar to 30 minutes during minor X-ray/radio outbursts and reestablishes within similar to 18 hr of a major outburst, indicating the robustness of the X-ray/radio (or disk/jet) system to disruption. At lower resolution (80-240 AU), more extended ejecta are imaged at similar to 500 AU separation from the stationary core. Time-lapse images clearly detect the superluminal motion of the ejecta in a few hours. The measured velocity is 1.5c + 0.1c (D/12 kpc) for the approaching component and is consistent with ballistic motion of the ejecta from 500 AU outward, perhaps even since birth. The axis of the ejecta differs by less than or equal to 12 degrees clockwise from the axis of the AU-scale jet, measured in the same observation. Both axes are stable in time (+/- 5 degrees), the AU scale for 2 yr and the large scale for over 4 yr. Astrometry over 2 yr relative to an extragalactic reference locates the black hole to +/-1.5 mas, and its secular parallax due to Galactic rotation is 5.8 +/- 1.5 mas yr(-1), consistent with a distance of 12 kpc. Finally, a limit of less than or equal to 100 km s(-1) is placed on its proper motion with respect to its neighborhood. Some accreting black holes of stellar mass (e.g., Cyg X-1, 1E 1740-2942, GRS 1758-258, GX 339-4) and supermassive black holes at the center of galaxies (e.g., Sgr A*) lack evidence of large flares and discrete transient ejecta but have compact radio cores with steady, hat-spectrum "plateau" states, like GRS 1915 + 105. To the present day GRS 1915 + 105 is the only system where both AU-scale steady jets and large-scale superluminal ejections have been unambiguously observed. Our observations suggest that the unresolved flat-spectrum radio cores of accreting black holes are compact quasi-continuous synchrotron jets.