LATEST NEWS

New equation of states for postmerger supramassive quark stars

Author: Ang Li* (XMU), Zhen-Yu Zhu (XMU), and Xia Zhou (XAO-CAS)
arXiv:1706.04720, ApJ (2017) accepted

Binary neutron star (NS) mergers with their subsequent fast-rotating supramassive magnetars are one attractive interpretation for at least some short gamma-ray bursts (SGRBs), based on the internal plateau commonly observed in the early X-ray afterglow. The rapid decay phase in this scenario signifies the epoch when the star collapses to a black hole after it spins down, and could effectively shed light on the underlying unclear equation of state (EoS) of dense matter. In the present work, we confront the protomagnetar masses of the internal plateau sample from representative EoS models, with the one independently from the observed galactic NS-NS binary, aiming to contribute new compact star EoSs from SGRB observations...

Vertical Structure of Radiation-pressure-dominated Thin Disks: Link between Vertical Advection and Convective Stability

Author: Hong-Yu Gong and Wei-Min Gu

Abstract: In the classic picture of standard thin accretion disks, viscous heating is balanced by radiative cooling through the diffusion process, and the radiation-pressure-dominated inner disk suffers convective instability. However, recent simulations have shown that, owing to the magnetic buoyancy, the vertical advection process can significantly contribute to energy transport...

Nanqiang seminar: In Search of Our Cosmic Origins

Title: In Search of Our Cosmic Origins

Speaker: Asso. Prof. Jonathan C. Tan
Institute: University of Florida
Time: 2017.4.17(Monday) 14:30
Place: Teaching Building 302, Haiyun Campus, Xiamen University

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...

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