Jets at lowest mass accretion rates

Abstract

Abstract. We present results of recent observations and theoretical modeling of data from black holes accreting at very low luminosities (L/L E dd 10 −8 ). We discuss our newly developed time-dependent model for episodic ejection of relativistic plasma within a jet framework, and a successful application of this model to describe the origin of radio flares seen in Sgr A*, the Galactic center black hole. Both the observed time lags and size-frequency relationships are reproduced well by the model. We also discuss results from new Spitzer data of the stellar black hole X-ray binary system A0620-00. Complemented by long term SMARTS monitoring, these observations indicate that once the contribution from the accretion disk and the donor star are properly included, the residual mid-IR spectral energy distribution of A0620-00 is quite flat and consistent with a non-thermal origin. The results above suggest that a significant fraction of the observed spectral energy distribution originating near black holes accreting at low luminosities could result from a mildly relativistic outflow. The fact that these outflows are seen in both stellar-mass black holes as well as in supermassive black holes at the heart of AGNs strengthens our expectation that accretion and jet physics scales with mass.

Polarized synchrotron emission in quiescent black hole X-ray transients

“…At longer wavelengths, a mid-IR excess above the companion emission, at a similar flux density to the radio emission, was interpreted as either dust from a circumbinary disc around the A0620-00 system, or synchrotron emission from quiescent jets in the system (Muno & Mauerhan 2006;Gallo et al 2007). The non-stellar IR emission was found to be flat and variable (Maitra et al 2011), supporting the jet interpretation, and the spectral break in the jet spectrum was identified ) at a frequency of (1.3 ± 0.5) × 10 14 Hz (or 1.7-3.6 µm). Froning et al (2011) found that an upturn in the SED in A0620-00 in the far-UV could be explained by the extension of the optically thin synchrotron power law and is consistent with the jet model of Gallo et al (2007).…”

ALMA observations of A0620–00: fresh clues on the nature of quiescent black hole X-ray binary jets

“…This "flickering" component is stronger at longer wavelengths, with a fractional rms amplitude of ∼ 15-24 per cent at optical wavelengths, rising to ∼ 42 per cent at (K-band) NIR wavelengths (Dinçer et al 2018). The spectral index of the variable component has been inferred by various authors to be steeply red at optical-NIR wavelengths (α = −1.4 to −0.7; Shahbaz et al 2004;Cantrell et al 2010;Dinçer et al 2018), and flat/slightly inverted at NIR (α ∼ 0.3 to 0.4; Cherepashchuk et al 2019) and mid-IR (α = 0.2 to 0.3 at 3.6-8.0 µm; Maitra et al 2011) wavelengths. Noting that the extrapolation of this non-stellar mid-IR spectrum of A0620-00 down to GHz frequencies was consistent with the radio flux measured by the VLA in 2005, Russell et al (2013a) concluded that the optically thick-to-thin jet break lies in the optical frequency range: 1.3 ± 0.5 × 10 14 Hz.…”

Polarized synchrotron emission in quiescent black hole X-ray transients

“…disc around the A0620-00 system, or synchrotron emission from quiescent jets in the system (Muno & Mauerhan 2006;Gallo et al 2007). The non-stellar IR emission was found to be flat and variable (Maitra et al 2011), supporting the jet interpretation, and the spectral break in the jet spectrum was identified (Russell et al 2013) at a frequency of (1.3 ± 0.5) × 10 14 Hz (or 1.7-3.6 µm). Froning et al (2011) found that an upturn in the SED in A0620-00 in the far-UV could be explained by the extension of the optically thin synchrotron power law and is consistent with the jet model of Gallo et al (2007).…”