It was proposed earlier that the relativistic ejections observed in microquasars could be produced by violent magnetic reconnection episodes at the inner disk coronal region. Here we revisit this model, which employs a standard accretion disk description and fast magnetic reconnection theory, and discuss the role of magnetic reconnection and associated heating and particle acceleration in different jet/disk accretion systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs).
Deep Dive into The role of magnetic reconnection on jet/accretion disk systems.
It was proposed earlier that the relativistic ejections observed in microquasars could be produced by violent magnetic reconnection episodes at the inner disk coronal region. Here we revisit this model, which employs a standard accretion disk description and fast magnetic reconnection theory, and discuss the role of magnetic reconnection and associated heating and particle acceleration in different jet/disk accretion systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs).
Supersonic jets are observed in several astrophysical systems, such as active galactic nuclei (AGNs), neutron star and black hole X-ray binaries, and low-mass young stellar objects (YSOs), and are probably also associated with gamma-ray bursts. The study of their origin, structure, and evolution helps to shed light on the nature of their compact progenitors, as they carry angular momentum, mass, energy, and magnetic field away from the sources.
The currently most accepted paradigm for jet production is based on the magneto-centrifugal acceleration out of a magnetized accretion disk that surrounds the central source. Firstly proposed by Blandford & Payne (1982; see also Lynden-Bell 1969;Blandford & Rees 1974;and Lovelace 1976, where these ideas initially germinated), this basic scenario for jet launching has been object of extensive analytical and numerical investigation (see e.g., McKinney & Blandford 2009;Shibata 2005; de Gouveia Dal Pino 2005 for reviews). However, though considerable progress has been achieved in the comprehension of the possible origin of the magnetic fields that must permeate the accretion disk and the mechanism of angular momentum transport that allows the accretion to occur through magnetorotational turbulence (Balbus & Hawley 1998), questions related to jet stability, the nature of the coupling between the central source magnetosphere and the disk field lines, and the quasi-periodic ejections that are often associated to these jets, are still debated.
Relativistic jets from stellar-mass black holes of binary stars emitting X-rays, also called microquasar jets (or BHXRB jets), are scaled-down versions of AGN (or quasar) jets, typically extending for ∼ 1pc and probably powered by the accreting, spinning black hole. Despite the enormous difference in scale, both classes share several similarities in their physical properties. However, because the characteristic times of the matter flow are proportional to the black hole mass, the accretion-ejection phenomena in microquasars end sooner and are about 10 -7 -10 -5 faster than analogous phenomena in quasars. This fact and their closer proximity to us (they are generally observable within the Galaxy) make the microquasars easier to investigate compared to the AGNs (Mirabel & Rodrigues 1999).
Although individual systems are complex and peculiar when looked at in detail, there are common features to all classes of BHXRBs (e.g, Remillard & McClintock, 2006). According to their x-ray emission (2-20 keV), they show basically two major states: a quiescent and an outburst state. The former is characterized by low x-ray luminosities and hard non-thermal spectra. Usually, transient BHXRBs exhibit this state for long periods, which allows one to obtain the physical parameters of the system as the spectrum of the secondary star becomes prominent.
On the other hand, the outburst state corresponds to intense activity and emission and can be sub-classified in three main active and many intermediary states. According to Remillard & McClintock (2006), the three main active states are the thermal state (TS), the hard state (HS) and the steep power law state (SPLS). These states are usually explained as changes in the structure of the accretion flow. During the TS, for example, the soft x-ray thermal emission comes from the inner region of the thin accretion disk that extends until the last stable orbits around the black hole. On the other hand, during the HS the observed weak thermal component suggests that the disk is truncated at a few hundreds/thousands gravitational radii. The hard x-ray emission measured during this state is often attributed to inverse Compton scattering of soft photons from the outer disk by relativistic electrons in the hot inner region of the system (e.g. Remillard & McClintock, 2006;Malzac, 2007).
A widely observed example from radio to x-rays is the microquasar GRS 1915+105. Located at a distance of ∼ 12.5 kpc and probably with a 10-18 solar mass black hole in the center of the binary system, it was the first galactic object to show evidence of superluminal radio ejection (Mirabel & Rodrigues, 1994;Mirabel & Rodrigues, 1998). Dhawan et al. (2000) have distinguished two main radio states of this system, a plateau and a flare state. During the plateau state the RXTE (2-12 keV) soft X-ray emission is weak, while the BATSE (20-100 keV) hard X-rays are strong and the radio flat spectrum is produced by a small scale nuclear jet. On the other hand optically thin ejecta are superluminally expelled up to thousands of AU during the flare phase and the radio spectral index is between 0.5 and 0.8. The soft X-rays also flare during this phase and exhibit a high variability, while the hard X-rays fade for a few days before recovering. In terms of the x-ray spectral states, several works have verified that the radio flares of this source occur during the SPLS (e.g., Fender et al., 2004) and the x-ray emission of both the plateau and the fla
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