Black Hole Accretion in Gamma Ray Bursts

Abstract

Abstract:We study the structure and evolution of the hyperaccreting disks and outflows in the gamma ray bursts central engines. The torus around a stellar mass black hole is composed of free nucleons, Helium, electron-positron pairs, and is cooled by neutrino emission. Accretion of matter powers the relativistic jets, responsible for the gamma ray prompt emission. The significant number density of neutrons in the disk and outflowing material will cause subsequent formation of heavier nuclei. We study the process of nucleosynthesis and its possible observational consequences. We also apply our scenario to the recent observation of the gravitational wave signal, detected on 14 September 2015 by the two Advanced LIGO detectors, and related to an inspiral and merger of a binary black hole system. A gamma ray burst that could possibly be related with the GW150914 event was observed by the Fermi satellite. It had a duration of about 1 s and appeared about 0.4 s after the gravitational-wave signal. We propose that a collapsing massive star and a black hole in a close binary could lead to the event. The gamma ray burst was powered by a weak neutrino flux produced in the star remnant's matter. Low spin and kick velocity of the merged black hole are reproduced in our simulations. Coincident gravitational-wave emission originates from the merger of the collapsed core and the companion black hole.

Disks around merging binary black holes: From GW150914 to supermassive black holes

“…Circumbinary disks were proposed because inspiraling and merging BHBHs in vacuum do not generate EM signals, but they may do so in the presence of ambient gas, such as binaries residing in AGNs [24,25] or those with gas remaining from their stellar progenitors [26][27][28][29]. There are multiple papers that suggest possible connections between LIGO GW150914 and GW150914-GBM, see, e.g., [27,30,31]. Sources that could generate both the GWs and the hard X-rays reported include binary black hole-neutron stars, binary black holemassive stars, and rapidly rotating massive stars.…”

Astrophysical Prior Information and Gravitational-Wave Parameter Estimation

“…Kilonovae and macronovae in the optical and near-infrared range may be triggered by rapid neutron capture in ejecta Lattimer and Schramm (1976); Li and Paczyński (1998), and would last hours to weeks. Stellarmass BHBH binaries, in contrast, are not expected to generate EM counterparts except for in quite exotic environments (although the detection in Connaughton et al (2016) has resulted in a flurry of new proposed mechanisms Zhang (2016); Yamazaki et al (2016); Morsony et al (2016); Fraschetti (2016); Malafarina and Joshi (2016); Janiuk et al (2016); Liebling and Palenzuela (2016); Loeb (2016); Perna et al (2016); Stone et al (2017)).…”

Distributions of Energy, Luminosity, Duration, and Waiting Times of Gamma-Ray Burst Pulses with Known Redshift Detected by Fermi/GBM

“…The nature of the central engine that powers a GRB is still debated, as either a hyper-accreting stellar-mass black hole (BH; Lei et al 2013;Janiuk et al 2017;Sado 2019) surrounded by a thick accretion disk, or a fast-rotating, highly magnetized neutron star (NS, known as a "millisecond magnetar"; Usov 1992;Wheeler et al 2000;Thompson et al 2004;Metzger et al 2011). In the case of a hyper-accreting BH, the jet can be produced either by a neutrino-dominated accretion flow (NDAF; Liu et al 2017) in which neutrinos tap the thermal energy of the accretion disk via neutrino-antineutrino annihilation, launching a thermally dominated fireball (Popham et al 1999;Di Matteo et al 2002), or through the Blandford-Znajek (BZ) effect (Blandford & Znajek 1977), which converts the BH spinning energy into a Poynting-flux-dominated outflow.…”