Magnetically Torqued Neutrino-Dominated Accretion Flows for Gamma-Ray Bursts

Abstract

Recent observations and theoretical work on gamma-ray bursts (GRBs) favor the central engine model of a Kerr black hole (BH) surrounded by a magnetized neutrino-dominated accretion flow (NDAF). The magnetic coupling between the BH and disk through a large-scale closed magnetic field exerts a torque on the disk, and transports the rotational energy from the BH to the disk. We investigate the properties of the NDAF with this magnetic torque. For a rapid spinning BH, the magnetic torque transfers enormous rotational energy from BH into the inner disk. There are two consequences: (i) the luminosity of neutrino annihilation is greatly augmented; (ii) the disk becomes thermally and viscously unstable in the inner region, and behaves S-Shape of the surface density versus accretion rate.It turns out that magnetically torqued NDAF can be invoked to interpret the variability of gamma-ray luminosity. In addition, we discuss the possibility of restarting the central engine to produce the X-ray flares with required energy.Subject headings: accretion, accretion disk-black hole physics -magnetic fieldsgamma rays: bursts -neutrinos Recently, the magnetic coupling (MC) between the central spinning BH and their surrounding accretion disk has been paid much attention (e.g. Blandford 1999;van Putten 1999;Li & Paczynski 2000;Li 2002;Wang et al. 2002). As a variant of the BZ process, the MC process exerts a torque on the disk, and transports the rotational energy from the BH to the disk. The effects of MC torque has been discussed in some disk models, for example, Lai (1998) and Lee (1999) in a neutron star with slim disk, Li (2002), Wang et al. (2002Wang et al. ( , 2003, Kluzniak and Rappaport (2007) in a compact object with thin disk, Ye et al. (2007) and Ma et al. (2007) in a BH with advection-dominated accretion flow (ADAF). It is found, the disk properties are greatly changed and its luminosity is augmented significantly due to the rotational energy of BH extracted in the MC process. Therefore, it is attractive for us to investigate the effects of MC torque on NDAF. To highlight the effects of MC torque, we ignore other MHD process, such as BZ and BP mechanism, and we refer to this model as MCNDAF.This paper is organized as follows. In Sect. 2 we describe the MCNDAF model, which is a relativistic steady state thin disk. The effects of MHD stress are described by the dimensionless parameter α. The main equations are based on DPN02 and NPK01.Recently, GLL06, Chen & Beloborodov (2006) and Shibata et al. (2006Shibata et al. ( , 2007 argued that the general relativistic (GR) effects are important for NDAF, so we introduce GR correction factors to the equations. The MC torque appears in the angular momentum equation.

Open questions in GRB physics

“…It is possible that both mechanisms (neutrino annihilation and BZ process) are operating in BH-torus systems. A variable outflow can be due to the interplay between the magnetic fields and the accreting materials [103,104]. For a jet emerging from a star, jet propagation instabilities in the envelope can give rise to further variabilities in the outflow [96,97].…”

Numerical and Analytical Solutions of Neutrino-Dominated Accretion Flows With a Non-Zero Torque Boundary Condition and Its Applications in Gamma-Ray Bursts

“…In these works, the magnetic stress in the plunging region is likely the origin of the non-zero torque at inner disk edge. For simplicity, we roughly take the magnetic coupling torque exacted by BH as the upper limit of such boundary torque Lei et al (2009). Nonetheless, there are two differences at least between the nztNDAF model in this work and the MCNDAF model in Lei et al (2009).…”

“…The NDAF has been extensively investigated and usually compared with the magnetic mechanism (e.g., Narayan et al 2001, hereafter NPK01;Kohri & Mineshige 2002;Di Matteo et al 2002, hereafter DPN02;Chen & Beloborodov 2007;Janiuk et al 2004Janiuk et al , 2007Janiuk et al , 2010Gu et al 2006;Liu et al 2007; Lei et al 2008Lei et al , 2009Lei et al , 2013a. It was for a long time considered as an inefficient model for GRBs.…”

“…This suggests a link between ∆ǫ (as well as η) and BH spin. As we known, spin energy and angular momentum can be transferred from the BH to the disk via a large-scale closed magnetic field (Blandford 1999;van Putten 1999;Li & Paczynski 2000;Li 2000Li , 2002Wang et al 2002Wang et al , 2003Gan et al 2007;Lei et al 2007Lei et al , 2009). This mechanism is called magnetic coupling process (MC).…”

Signature of a Newborn Black Hole from the Collapse of a Supra-massive Millisecond Magnetar

“…We also assume a turn-off time of the BH central engine t f , beyond which the tail emission from jet fades as t −(2+β) , where β is the spectral index. The hyper-accreting BH system can launch a relativistic jet via neutrino-antineutrino annihilation (Popham et al 1999;Narayan et al 2001;Di Matteo et al 2002;Gu et al 2006;Chen & Beloborodov 2007;Janiuk et al 2004Janiuk et al , 2007Liu et al 2007Liu et al , 2015Lei et al 2009Lei et al , 2017Xie et al 2016), or Blandford-Znajek mechanism (hereafter BZ; (Blandford & Znajek 1977;Lee et al 2000;Li 2000;Lei et al 2005Lei et al , 2013). The neutrino annihilation mechanism suffers strong baryon loading from the disk and therefore may be too "dirty" to account for a GRB jet Xie et al 2017).…”