LATEST NEWS

Vertical Advection Effects on Hyper-accretion Disks and Potential Link between Gamma-Ray Bursts and Kilonovae

Authors: Tuan Yi, Wei-Min Gu, Feng Yuan, Tong Liu, and Hui-Jun Mu

Recent simulations on super-Eddington accretion flows have shown that, apart from the diffusion process, the vertical advection based on magnetic buoyancy can be a more efficient process to release the trapped photons in the optically thick disk. As a consequence, the radiative luminosity from the accretion disk can be far beyond the Eddington value. Following this spirit, we revisit the structure and radiation of hyper-accretion disks with mass accretion rates in the range of 10-3〜10 Ms-1...

CENTRAL ENGINE OF LATE-TIME X-RAY FLARES WITH INTERNAL ORIGIN

Author: Hui-Jun Mu, Wei-Min Gu, Shu-Jin Hou, Tong Liu, Da-Bin Lin, Tuan Yi, En-Wei Liang, and Ju-Fu Lu

This work focuses on a sample of seven extremely late-time X-ray flares with peak time tp > 104 s , among which two flares can be confirmed as the late-time activity of central engine. The main purpose is to investigate the mechanism of such late-time flares based on the internal origin assumption. In the hyper-accreting black hole (BH) scenario, we study the possibility of two well-known mechanisms acting as the central engine to power such X-ray flares, i.e., the neutrino–antineutrino annihilation and the Blandford–Znajek (BZ) process...

Internal x-ray plateau in short GRBs: Signature of supramassive fast-rotating quark stars?

A supramassive, strongly magnetized millisecond neutron star (NS) has been proposed to be the candidate central engine of at least some short gamma-ray bursts (SGRBs), based on the “internal plateau” commonly observed in the early x-ray afterglow. While a previous analysis shows a qualitative consistency between this suggestion and the Swift SGRB data, the distribution of observed break time tb is much narrower than the distribution of the collapse time of supramassive NSs for the several NS equations-of-state (EoSs) investigated.
Recently, a team of astronomers from Xiamen University, led by associate Professor Ang Li, study four recently constructed “unified” NS EoSs (BCPM, BSk20, BSk21, and Shen) as well as three developed strange quark star (QS) EoSs within the new confinement density-dependent mass (CDDM) model, labelled as CIDDM, CDDM1, and CDDM2...

Delta effects in density-dependent relativistic Hartree-Fock theory and neutron stars

Recently, a team of astronomers from Xiamen University, led by associate Professor Ang Li, has extended the density-dependent relativistic Hartree-Fock (DDRHF) theory to include Delta-isobars for the study of dense nuclear matter and neutron stars. To this end, they solve the Rarita-Schwinger equation for spin-3/2 particle. Both the direct and exchange terms of the Delta-isobars' self-energies are evaluated in details. In comparison with the relativistic mean field theory (Hartree approximation), a weaker parameter dependence is found for DDRHF...

Fast radio bursts and their gamma-ray or radio afterglows as Kerr-Newman black hole binaries

Fast radio bursts (FRBs) are radio transients lasting only about a few milliseconds. They seem to occur at cosmological distances. We propose that these events can be originated in the collapse of the magnetosphere of Kerr-Newman black holes (KNBHs). We show that the closed orbits of charged particles in the magnetosphere of these objects are unstable. After examining the dependencies on the specific charge of the particle and the spin and charge of the KNBH, we conclude that the resulting timescale and radiation mechanism fit well with the extant observations of FRBs ...

Detectable MeV neutrinos from black hole neutrino-dominated accretion flows

Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/anti-neutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN)...

more news...