Relativistic Jets in the RXTE Era

Abstract

Abstract.Since the launch of the Rossi X-ray Timing Explorer in 1995 our understanding of jetted outflows has significantly improved. Indeed, relativistic jets are now believed to be a fairly ubiquitous property of accreting compact objects, that are intimately coupled with the accretion history. In this review, we summarize the observational connections in X-ray binaries between accretion flows and relativistic outflows (especially the relation with the X-ray states). We emphasize those aspects that have significantly benefited from the RXTE experiment, including the role that jets could play at high energies. We also review recent observations of large scale relativistic jets that could point to their long term effects on the interstellar medium. BLACK HOLE CANDIDATES AND X-RAY STATESBlack hole candidates (hereafter BH, even if its mass function has not been measured) are known to exhibit several X-ray spectral states, distinguished by the presence or absence of a soft black-body component at ∼ 1 keV (arising from the accretion disk) and the luminosity and spectral slope of emission at harder energies (whose nature is still the subject of an active debate). Systems in the low-hard state (LHS) have power-law X-ray spectra with a photon index in the range 1.4-1.9, an exponential cutoff (but not always) around 100 keV, and no (or only weak) evidence of a soft thermal component. In the LHS, the power density spectrum (PDS) is characterized by a strong band-limited noise power continuum. At higher soft X-ray flux 1 , these systems are usually found in the thermal-dominant (TD) or high-soft (HS) state. In that case, the X-ray spectrum is dominated (up to ∼ 90%) by the soft-thermal component, with an additional weak and steep power-law component (with no apparent cut-off) at higher energy. very weak residual X-ray emission that displays many similarities with the LHS [e.g. 4,5]. This implies that the QS could simply be a low luminosity version of the LHS. With the detailed coverage by RXTE of spectral properties of BHs during recent outbursts, the different X-ray states can be well illustrated using a HardnessIntensity diagram (see Fig. 1 from [6]). In this case, the VHS and IS are defined as various tracks between the vertical tracks (of constant hardness) of the HS and LHS [2,6]. For further details on the spectral states of BH, see [3]. In the sections that follow, we discuss the general properties of BHs in the various X-ray states, some of which they have in common with neutron star (NS) systems, and focus on relativistic jets in the light of recent developments based on multi-wavelength observations (including RXTE). For a detailed reviews of jets in X-ray binaries, see [7].