AU‐Scale Synchrotron Jets and Superluminal Ejecta in GRS 1915+105

Abstract

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 ∼10λ 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 ≥10 9 K, and its properties are better fit by a conically expanding synchrotron jet model, rather than a thermal jet. The nuclear jet varies in ∼30 min during minor X-ray/radio outbursts, and re-establishes within ∼18 hours 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 ∼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 1.5±0.1 c (D/12 kpc) for the approaching component, and is consistent with ballistic motion of the ejecta from 500 AU outwards, perhaps even since birth.The axis of the ejecta differs by ≤12 • clockwise from the axis of the AU-scale jet, measured in the same observation. Both axes are stable in time (±5 • ), the AU scale for two years, and the large scale for over four years. Astrometry over two years 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 ≤100 km s −1 is placed on its proper-motion with respect to its neighbourhood.Some accreting black holes of stellar mass (e.g. Cyg X-1, 1E 1740-2942, GRS 1758 and supermassive black holes at the centre of galaxies (e.g. Sgr A * ) lack evidence of large flares and discrete transient ejecta, -3but have compact radio cores with steady, flat-spectrum 'plateau' states, like GRS 1915+105. Until now GRS 1915+105 is the only system where both AUscale 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.

The Radio Quiescence of Active Galaxies with High Accretion Rates

“…Typically, at low X-ray luminosity, during which the accretion flow is thought to transform into a quasi-spherical RIAF radiating at L bol /L Edd ∼ <0.01 (Esin et al 1997), the spectrum is nonthermal and hard (the "low/hard" state). This state is usually accompanied by persistent, flat-spectrum radio emission, correlated with the X-ray emission and likely including a jet component (e.g., Dhawan et al 2000;Stirling et al 2001;Corbel et al 2003;. At higher X-ray luminosities (0.01 ∼ < L bol /L Edd ∼ <0.3), a conventional optically thick, geometrically thin disk (Shakura & Sunyaev 1973) produces a spectrum dominated by thermal, soft X-ray emission (the "high/soft" state), during which the radio emission is quenched (Tananbaum et al 1972;Fender et al 1999Gallo et al 2003;Tigelaar et al 2004).…”

Constraints on relativistic jets in quiescent black hole X-ray binaries from broad-band spectral modelling

“…Regardless, it is well-established that hard state BHXBs are associated with compact radio emission, which is interpreted as optically thick synchrotron radiation from the partially self-absorbed flat spectral component of a compact relativistic jet (Blandford & Königl 1979;Hjellming & Johnston 1988;Fender 2001). The compact jet typically remains unresolved in the radio, except for in a handful of cases with high (very long baseline interferometric) spatial resolution imaging (e.g., GRS 1915+105; Cyg X-1; Dhawan, Mirabel & Rodríguez 2000;Stirling et al 2001). The compact jet becomes optically thin around nearinfrared (NIR) frequencies (∼10 12 -10 14 Hz; Corbel & Fender 2002;Russell et al 2013), and synchrotron radiation from this optically thin component can sometimes extend into the X-ray waveband (e.g., Markoff, Falcke & Fender 2001;Markoff et al 2003;Russell et al 2010Russell et al , 2013.…”

Searching for the 511 keV annihilation line from galactic compact objects with the IBIS gamma ray telescope

“…The study of the jets from microquasars makes use of radio and X-ray observations (for a recent review see Gallo 2010). The jet interpretation of the radio emission was confirmed by the milliarcseconds scale jets observed in Cygnus X-1 (Stirling et al 2001) and GRS 1915+105 (Dhawan et al 2000). In X-ray band, arcsecond scale jets have been observed for the first time in SS 433 with the Chandra X-ray observatory (Marshall et al 2002).…”