Neutrino-dominated accretion flows as the central engine of gamma-ray bursts

Abstract

Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) are plausible candidates for the central engines of gamma-ray bursts (GRBs). NDAFs are hyperaccretion disks with accretion rates in the range of around 0.001-10 M ⊙ s −1 , which have high density and temperature and therefore are extremely optically thick and geometrically slim or even thick. We review the theoretical progresses in studying the properties of NDAFs as well as their applications to the GRB phenomenology. The topics include: the steady radial and vertical structure of NDAFs and the implications for calculating neutrino luminosity and annihilation luminosity, jet power due to neutrino-antineutrino annihilation and Blandford-Znajek mechanism and their dependences on parameters such as BH mass, spin, and accretion rate, time evolution of NDAFs, effect of magnetic fields, applications of NDAF theories to the GRB phenomenology such as lightcurve variability, extended emission, X-ray flares, kilonovae, etc., as well as probing NDAFs using multi-messenger signals such as MeV neutrinos and gravitational waves.

Comparison of Gravitational Waves from Central Engines of Gamma-Ray Bursts: Neutrino-dominated Accretion Flows, Blandford–Znajek Mechanisms, and Millisecond Magnetars

“…Before the central BHs or magnetars are born to power GRBs, the compact binary mergers and collapsars are also important GW sources (e.g., Cutler & Thorne 2002;Postnov & Yungelson 2014;Liu et al 2017). We here restrict ourselves only on the GWs from the GRB central engines.…”

“…Furthermore, BZ mechanism can power a GRB more easily than NDAFs, as demonstrated in Section 3.1. Those are summarized in the left panel of Figure 3 (adapted from Figure 20 in Liu et al (2017)): First, almost all SGRBs might be described in the NDAF model, with reasonable disk masses derived from the remanent of the compact objects mergers (Liu et al 2015c); Second, only about half of LGRBs might satisfy the NDAF model, while it might be necessary for the left half to introduce massive disks, extreme Kerr BHs, and high conversion efficiency for neutrino annihilation (Song et al 2016); Third, for LGRBs and ULGRBs, BZ mechanism is especially more efficient than NDAFs. Actually, the deviation between BZ mechanism and NDAFs is more significant if X-ray flares are included 1 (e.g., Liu et al 2015b;Luo et al 2013;Mu et al 2016); Fourth, the millisecond magnetar model could cover almost all types of GRBs as said before.…”

“…Long-duration GRBs (LGRBs) are usually regarded to be originated from the collapse of a massive star, while short-duration GRBs (SGRBs) are related to the merger events of black hole (BH)-neutron star (NS) or NS-NS binaries. In either case, the central engine of GRBs is likely to be a BH hyperaccretion system (see reviews by Liu et al 2017) or a massive millisecond magnetar (or protomagnetar, e.g., Duncan & Thompson 1992;Usov 1992;Dai & Lu 1998;Zhang & Mészáros 2001;Dai et al 2006;Metzger et al 2011).…”

Black Hole Hyperaccretion Inflow–Outflow Model. I. Long and Ultra-long Gamma-Ray Bursts

“…This suggests that the BZ mechanism is favored to power GRBs with long activity durations. Moreover, considering the strong outflow from the disk, the inner accretion rate is essentially always lower than the ignition accretion rate of NDAFs (for a * = 0.95 and the viscosity parameter α = 0.1, the ignition accretion rate is about 0.021 M ⊙ s −1 , where M ⊙ is the mass of Sun, see e.g., Chen & Beloborodov 2007;Zalamea & Beloborodov 2011;Liu et al 2017).…”

“…For the BH case, the fall back matter triggers the BH hyperaccretion processes to power a relativistic jet breaking out from the envelope via neutrino-antineutrino annihilation mechanism liberating the gravitational energy of the BH (e.g., Ruffert et al 1997;Rosswog et al 2003), which corresponds to neutrino-dominated accretion flows (Popham et al 1999;Di Matteo et al 2002;Gu et al 2006;Liu et al 2007;Kawanaka & Mineshige 2007;Zalamea & Beloborodov 2011;Xue et al 2013;Liu et al 2016;Song et al 2016), or the Blandford-Znajek (BZ) mechanism tapping the rotational energy of the BH (e.g., Blandford & Znajek 1977;Lee et al 2000a,b;Wu et al 2013;Lei et al 2013Lei et al , 2017Liu et al 2015). For a recent review on GRB NDAFs, see Liu et al (2017). For the NS case, the spin down of a NS with a millisecond rotation period and a strong magnetic field (millisecond mag- netar) extracting the rotational energy by electromagnetic torques can produce LGRBs, even superluminous SNe (e.g., Duncan & Thompson 1992;Usov 1992;Dai & Lu 1998a,b;Kluźniak & Ruderman 1998;Zhang & Mészáros 2001;Dai et al 2006;Metzger et al 2011Metzger et al , 2015Lü et al 2015).…”