Neutrino Annihilation Luminosity Research Articles

Neutrino Oscillation Effects on the Luminosity of Neutrino-dominated Accretion Flows around Black Holes

A stellar-mass black hole surrounded by the neutrino-dominated accretion flow (NDAF) has been proposed as the central engine of gamma-ray bursts. In this work, we investigate the neutrino/antineutrino luminosity and annihilation luminosity from the NDAF and pair annihilation model, taking into account the neutrino oscillation above the accretion disk. The disk's hydrodynamical properties are modeled using an empirical solution previously derived with boundary conditions, including the effect of electron degeneracy and neutrino trapping. Our key parameters are the mass accretion rate and the black hole spin given in the ranges of Ṁ=0.1 –10 M ⊙ s−1 and 0 ≤ a < 1, respectively. Without neutrino oscillation, the obtained neutrino/antineutrino luminosity is ∼1051–1053 erg s−1, while the neutrino annihilation luminosity is found to be ∼1046–1051 erg s−1. In the presence of neutrino oscillation in the vacuum limit, the electron neutrino annihilation luminosity decreases by ≲22% through the flavor transformation, while the muon and tau neutrino luminosity can increase by up to ∼45% and 60%, respectively. As a result, the total annihilation luminosity can be reduced by up to ∼19% due to the oscillation process above the disk. Finally, we also investigate the case whereby the charge-conjugation-parity-symmetry-violating (CP-violating) phase is changed from δCP = 0° to 245°. However, our results reveal that the CP-violating phase has minimal impact on the neutrino annihilation luminosity.

Neutrinos and gravitational waves from magnetized neutrino-dominated accretion discs with magnetic coupling

ABSTRACT Gamma-ray bursts (GRBs) might be powered by black hole (BH) hyperaccretion systems via the Blandford–Znajek (BZ) mechanism or neutrino annihilation from neutrino-dominated accretion flows (NDAFs). Magnetic coupling (MC) between the inner disc and BH can transfer angular momentum and energy from the fast-rotating BH to the disc. The neutrino luminosity and neutrino annihilation luminosity are both efficiently enhanced by the MC process. In this paper, we study the structure, luminosity, MeV neutrinos, and gravitational waves (GWs) of magnetized NDAFs (MNDAFs) under the assumption that both the BZ and MC mechanisms are present. The results indict that the BZ mechanism will compete with the neutrino annihilation luminosity to trigger jets under the different partitions of the two magnetic mechanisms. The typical neutrino luminosity and annihilation luminosity of MNDAFs are definitely higher than those of NDAFs. The typical peak energy of neutrino spectra of MNDAFs is higher than that of NDAFs, but similar to those of core-collapse supernovae. Moreover, if the MC process is dominant, then the GWs originating from the anisotropic neutrino emission will be stronger particularly for discs with high accretion rates.

EVOLUTIONS OF STELLAR-MASS BLACK HOLE HYPERACCRETION SYSTEMS IN THE CENTER OF GAMMA-RAY BURSTS

A neutrino-dominated accretion disk around a stellar-mass black hole (BH) can power a gamma-ray burst (GRB) via annihilation of neutrinos launched from the disk. For the BH hyperaccretion system, high accretion rate should trigger the violent evolution of the BH's characteristics, which further leads to the evolution of the neutrino annihilation luminosity. In this paper, we consider the evolution of the accretion system to analyze the mean time-dependent neutrino annihilation luminosity with the different mean accretion rates and initial BH parameters. By time-integrating the luminosity, the total neutrino annihilation energy with the reasonable initial disk mass can satisfy the most of short-duration GRBs and about half of long-duration GRBs. Moreover, the extreme Kerr BH should exist in the cental engines of some high-luminosity GRBs. GRBs with higher energy have to request the alternative magnetohydrodynamics processes in the centers, such as the Blandford-Znajek jet from the accretion system or the millisecond magnetar.

The mass of the neutrino-dominated accretion disks in short gamma-ray bursts

The coalesence of compact binary systems might be the plausible candidate to power short Gamma-Ray Bursts (GRBs), since in this scenario a low mass disk can be formed, and the lifetime of the disk is comparable to the duration of the short GRBs. After merger, a neutrino-dominated accretion flow (NDAF) surrounding a stellar-mass black hole (BH) will be formed and neutrino-antineutrino annihilation above the disk may power short GRBs. The results of the simulation show that the disk mass of the NDAF has a limit after merger events. So the question is: can annihilations of neutrinos from NDAFs owning such disk masses power all the observed short GRBs? Using the current short GRB observational data and fireball model, we estimate the disk mass of the NDAF. The neutrino annihilation luminosity as a function of BH spin and accretion rate is fitted from the global solutions of NDAFs. The results show that the estimation of the disk mass mainly depends on its output energy, jet opening angle, and central BH characteristic of GRBs. And some short GRBs require massive disks, which approach or exceed the limits in simulations. If the precise value of jet opening angle is considered, the real requirements of the disk masses will be much larger than the present results, since we use only the lower limit of them in the calculation. These results reflect that the neutrino annihilation process is deficient to power short GRBs. We suggest that there may exit other magnetohydrodynamic processes or some mechanisms to increase the efficiency of the neutrino emission, and then provide energy to power short GRBs.

NEUTRINO-COOLED ACCRETION MODEL WITH MAGNETIC COUPLING FOR X-RAY FLARES IN GAMMA-RAY BURSTS

The neutrino-cooled accretion disk, which was proposed to work as the central engine of gamma-ray bursts, encounters difficulty in interpreting the X-ray flares after the prompt gamma-ray emission. In this paper, the magnetic coupling (MC) between the inner disk and the central black hole (BH) is taken into consideration. For mass accretion rates around 0.001 ∼ 0.1 M☉ s−1, our results show that the luminosity of neutrino annihilation can be significantly enhanced due to the coupling effects. As a consequence, after the gamma-ray emission, a remnant disk with mass Mdisk ≲ 0.5 M☉ may power most of the observed X-ray flares with the rest frame duration less than 100 s. In addition, a comparison between the MC process and the Blandford–Znajek mechanism is shown on the extraction of BH rotational energy.

Possible Outflow Formation in the Central Engine of GRBs

We investigate the vertical structure of neutrino-dominated accretion flows in spherical coordinates. In our calculation, the empty funnel along the rotation axis can naturally explain the neutrino annihilable ejection. The outflow is possible due to the positive Bernoulli function, and the luminosity of neutrino annihilation is enhanced by one or two orders of magnitude.

VERTICAL STRUCTURE OF NEUTRINO-DOMINATED ACCRETION DISK AND APPLICATIONS TO GAMMA-RAY BURSTS

We revisit the vertical structure of neutrino-dominated accretion flows in spherical coordinates. We stress that the flow should be geometrically thick when advection becomes dominant. In our calculation, the luminosity of neutrino annihilation is enhanced by one or two orders of magnitude. The empty funnel along the rotation axis can naturally explain the neutrino annihilable ejection.

HYPERACCRETING NEUTRON STAR DISKS AND NEUTRINO ANNIHILATION

Newborn neutron stars surrounded by hyperaccreting and neutrino-cooled disks may exist in some gamma-ray bursts and/or supernovae. In this paper, we further study the structure of such a neutron star disk based on the two-region (i.e., inner and outer) disk scenario following our previous work, and calculate the neutrino annihilation luminosity from the disk in various cases. We investigate the effects of the viscosity parameter {alpha}, energy parameter {epsilon} (measuring the neutrino cooling efficiency of the inner disk), and outflow strength on the structure of the entire disk as well as the effect of emission from the neutron star surface boundary emission on the total neutrino annihilation rate. The inner disk satisfies the entropy-conservation self-similar structure for the energy parameter {epsilon} {approx_equal} 1 and the advection-dominated structure for {epsilon} < 1. An outflow from the disk decreases the density and pressure but increases the thickness of the disk. Moreover, compared with the black hole disk, the neutrino annihilation luminosity above the neutron star disk is higher, and the neutrino emission from the boundary layer could increase the neutrino annihilation luminosity by about one order of magnitude higher than the disk without boundary emission. The neutron star disk with the advection-dominatedmore » inner disk could produce the highest neutrino luminosity while the disk with an outflow has the lowest. Although a heavily mass-loaded outflow from the neutron star surface at early times of neutron star formation prevents the outflow material from being accelerated to a high bulk Lorentz factor, an energetic ultrarelativistic jet via neutrino annihilation can be produced above the stellar polar region at late times if the disk accretion rate and the neutrino emission luminosity from the surface boundary layer are sufficiently high.« less

MAGNETICALLY TORQUED NEUTRINO-DOMINATED ACCRETION FLOWS FOR GAMMA-RAY BURSTS

Recent observations and theoretical work on gamma-ray bursts 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 the 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: (1) the luminosity of neutrino annihilation is greatly augmented; (2) the disk becomes thermally and viscously unstable in the inner region, displaying s-shaped curves of the surface density versus accretion rate. It turns out that the 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.

Structure and Luminosity of Neutrino‐cooled Accretion Disks

Neutrino-cooled hyperaccretion disks around stellar mass black holes are plausible candidates for the central engine of gamma-ray bursts. We calculate the one-dimensional structure and the annihilation luminosity of such disks. The neutrino optical depth is of crucial importance in determining the neutrino cooling rate and is in turn dependent on the electron fraction, the free nucleon fraction, and the electron degeneracy, with given density and temperature of the disk matter. We construct a bridging formula for the electron fraction that works for various neutrino optical depths, and give exact definitions for the free proton fraction and free neutron fraction. We show that the electron degeneracy has important effects in the sense that it enlarges the absorption optical depth for neutrinos, and it along with the neutronization processes favored by high temperature cause the electron fraction to drop to be below 0.1 in the inner region of the disk. The resulting neutrino annihilation luminosity is considerably reduced comparing with that obtained in previous works where the electron degeneracy was not considered and the electron fraction was simply taken to be 0.5, but it is still likely to be adequate for gamma-ray bursts, and it is ejected mainly from the inner region of the disk and has an anisotropic distribution.