Production of the large scale superluminal ejections of the microquasar GRS 1915+105 by violent magnetic reconnection

Abstract

We propose here that the large-scale superluminal ejections observed in the galactic microquasar GRS 1915+105 during radio flare events are produced by violent magnetic reconnection episodes in the corona just above the inner edge of the magnetized accretion disk that surrounds the central ∼10 M black hole. The process occurs when a large-scale magnetic field is established by a turbulent dynamo in the inner disk region with a ratio between the gas+radiation and the magnetic pressures β 1, implying a magnetic field intensity of ∼7 × 10 8 G. During this process, substantial angular momentum is removed from the disk by the wind generated by the vertical magnetic flux therefore increasing the disk mass accretion to a value near (but below) the critical one (Ṁ ∼ 10 19 g s −1 ). Part of the magnetic energy released by reconnection heats the coronal gas (T c 5 × 10 8 K) that produces a steep X-ray spectrum with luminosity L X 10 39 erg s −1 , consistent with observations. The remaining magnetic energy released goes to accelerate the particles to relativistic velocities (v ∼ v A ∼ c, where v A is the Alfvén speed) in the reconnection site through first-order Fermi processes. In this context, two possible mechanisms have been examined that produce power-law electron distributions N(E) ∝ E −α E , with α E = 5/2, 2, and corresponding synchrotron radio power-law spectra with spectral indices which are compatible with that observed during the flares (S ν ∝ ν −0.75,−0.5 ).

The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

“…Large scale magnetic reconnection events may be at the origin of large scale transient jets in microquasar systems (de Gouveia dal Pino & Lazarian 2005;de Gouveia Dal Pino et al 2010;Kowal et al 2011;Dexter et al 2014), for example via a magnetic field reversal accreted onto a magnetically arrested disk. Reconnection then occurs in the accretion disk coronae, near the black hole, where particle densities and magnetic fields are high.…”

“…It is a candidate for explaining (i) particle acceleration at pulsar wind termination shocks (Kirk & Skjaeraasen 2003;Pétri & Lyubarsky 2007;Sironi & Spitkovsky 2011a); (ii) the flat radio spectra from galactic nuclei and AGNs (Birk et al 2001) and from extragalactic jets (Romanova & Lovelace 1992); (iii) GeV flares from the Crab nebula (Bednarek & Idec 2011;Uzdensky et al 2011;Cerutti et al 2012aCerutti et al ,b, 2013; (iv) flares in active galactic nuclei (AGN) jets (Giannios et al 2009) or in gamma-ray bursts (Lyutikov 2006a;Lazar et al 2009); (v) the heating of AGN and microquasar coronae and the observed flares (Di Matteo 1998;Merloni & Fabian 2001;Goodman & Uzdensky 2008;Reis & Miller 2013;Romero et al 2014;Zdziarski et al 2014); (vi) the heating of the lobes of giant radio galaxies (Kronberg et al 2004); (vii) transient outflow production in microquasars and quasars (de Gouveia dal Pino & Lazarian 2005;de Gouveia Dal Pino et al 2010;Kowal et al 2011;Dexter et al 2014); (viii) gamma-ray burst outflows and non-thermal emissions (Drenkhahn & Spruit 2002;Giannios & Spruit 2007;McKinney & Uzdensky 2012); (ix) X-ray flashes (Drenkhahn & Spruit 2002); or (x) soft gamma-ray repeaters (Lyutikov 2006b;Uzdensky 2011).…”

The role of magnetic reconnection on jet/accretion disk systems

“…1. A detailed description of the scenario adopted is given in de Gouveia Dal Pino & Lazarian (2005). Here we briefly present the assumptions made.…”

“…Besides, because the reconnection mechanism is operating at the interface region between the inner disk and the central source, the choice of a geometrically thin accretion disk (rather than a thick one) is not a crucial point for our model. of the magnetic flux in this region (e.g., Merloni 2003;Livio et al 2003;Tagger et al 2004;de Gouveia Dal Pino & Lazarian 2005;McKinney & Blandford 2009). Even without any dynamo action, a net poloidal field could be built in the inner diskcorona region simply due to advection of existing magnetic flux from the large radii.…”

“…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 (de Gouveia Dal Pino & Lazarian 2005). Aims.…”