Transient Black Hole Binaries

Abstract

The last two decades have seen a great improvement in our understand- ing of the complex phenomenology observed in transient black-hole binary systems, especially thanks to the activity of the Rossi X-Ray Timing Explorer satellite, com- plemented by observations from many other X-ray observatories and ground-based radio, optical and infrared facilities. Accretion alone cannot describe accurately the intricate behavior associated with black-hole transients and it is now clear that the role played by different kinds of (often massive) outflows seen at different phases of the outburst evolution of these systems is as fundamental as the one played by the accretion process itself. The spectral-timing states originally identified in the X-rays and fundamentally based on the observed effect of accretion, have acquired new importance as they now allow to describe within a coherent picture the phenomenology observed at other wave- length, where the effects of ejection processes are most evident. With a particular focus on the phenomenology seen in the X-ray band, we review the current state-of-the-art of our knowledge of black hole transients, describing the accretion-ejection connection at play during outbursts through the evolution of the observed spectral-timing properties. Although we mainly concentrate on the ob- servational aspects of the global X-ray transient picture, we also provide physical insight to it by reviewing (when available) the theoretical explanations and models proposed to explain the observed phenomenology.Comment: 37 pages, 7 figures, to be published in: "Astrophysics of Black Holes - From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer: Astrophysics and Space Science Library. arXiv admin note: text overlap with arXiv:0708.0148 by other author

Hard X-ray variability of V404 Cygni during the 2015 outburst

“…1554 (EPOCH 1) and by Jenke et al (2016) using FERMI/GBM data. Similar anti-correlations are also found in other BHBs in the hard state (Esin et al 1998;Wardziński et al 2002;Rodriguez et al 2003;Motta et al 2009;Kajava et al 2016), supporting our identification of the hard branch with the hard state of prototypical BHBs (Belloni & Motta 2016). The F x -T e anti-correlation in the hard branch can be explained by the truncated disk/hot inner flow model (Esin et al 1997;Mayer & Pringle 2007), which assumes that at low luminosities the accretion disk is truncated at distances between a few tens and a few thousand gravitational radii from the BH, and only a small fraction of disk pho- tons reach the hot flow/comptonizing medium.…”

“…We have identified a hard branch in the F X -Γ diagram of V404 Cyg, reminiscent of the hard state branch of the BHB HID (Homan et al 2001;Belloni 2004;Fender et al 2004;Dunn et al 2010;Belloni & Motta 2016). The hard branch is occupied by the hardest spectra in our sample (Γ ≤ 1.7).…”

“…Black hole (BH) binary systems (BHBs) can go through various spectral states which are thought to be caused by changes in the accretion geometry and accretion rates close to the BH, although the actual details still remain debated (Remillard & McClintock 2006;Belloni & Motta 2016). The two most common states are the hard and the soft states (see, e.g., Done et al 2007;Poutanen & Veledina 2014 for review).…”

Giant Metrewave Radio Telescope Monitoring of the Black Hole X-Ray Binary, V404 Cygni during Its 2015 June Outburst

“…The outburst states contain both a thermal and a non-thermal X-ray component, and are usually classified as "hard" (low luminosity, dominated by the nonthermal component), "soft" (high luminosity, dominated by the thermal component), and "very high" or "steep power law" (high luminosity, containing both thermal and non-thermal components, and with a steep photon index, ≈ 2.5) (e.g. Remillard & McClintock 2006;Belloni & Motta 2016).…”

Blandford–Znajek mechanism in black holes in alternative theories of gravity

“…Steady jets commonly appear when the source is in the hard state, over a wide range of accretion luminosities. Transient jets show up when the source switches from the hard to the soft state at high accretion rates, but there is also some evidence of transient jets when the source moves from the soft to the hard state at low accretion rates before returning to quiescence [2]. The mechanism for the formation of jets is currently unknown.…”