Hyper-accreting black hole as GRB central engine. I: Baryon loading in GRB jets

A hyper-accreting stellar-mass black hole has been long speculated as the best candidate of central engine of gamma-ray bursts (GRBs). Recent rich observations of GRBs by space missions such as Swift and Fermi pose new constraints on GRB central engine models. In this paper, we study the baryon loading processes of a GRB jet launched from a black hole central engine. We consider a relativistic jet powered by $\nu \bar\nu$-annihilation or by the Blandford-Znajek (BZ) mechanism. We consider baryon loading from a neutrino-driven wind from a neutrino-cooling-dominated accretion flow. For a magnetically dominated BZ jet, we consider neutron-drifting from the magnetic wall surrounding the jet and subsequent positron capture and proton-neutron inelastic collisions. The minumim baryon loads in both types of jet are calculated. We find that in both cases, a more luminous jet tends to be more baryon poor. A neutrino-driven "fireball" is typically "dirtier" than a magnetically dominated jet, while a magnetically dominated jet can be much cleaner. Both models have the right scaling to interpret the empirical $\Gamma-L_{\rm iso}$ relation discovered recently. Since some neutrino-driven jets have too much baryon loading as compared with the data, we suggest that at least a good fraction of GRBs should have a magnetically dominated central engine.Comment: 9 pages, 2 figures; Accepted for publication in Ap

Constructing an overall dynamical model for a system with changing design parameter properties

This study considers the identification problem for a class of non-linear parameter-varying systems associated with the following scenario: the system behaviour depends on some specifically prescribed parameter properties, which are adjustable. To understand the effect of the varying parameters, several different experiments, corresponding to different parameter properties, are carried out and different data sets are collected. The objective is to find, from the available data sets, a common parameter-dependent model structure that best fits the adjustable parameter properties for the underlying system. An efficient Common Model Structure Selection (CMSS) algorithm, called the Extended Forward Orthogonal Regression (EFOR) algorithm, is proposed to select such a common model structure. Two examples are presented to illustrate the application and the effectiveness of the new identification approach

Triangle singularity in the J/ψ→K+K−f0(980)(a0(980))J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980)) decays

We study the $J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980))$ reaction and find that the mechanism to produce this decay develops a triangle singularity around $M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515$~MeV. The differential width $d\Gamma / dM_{\rm inv}(K^- f_0/K^- a_0)$ shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the $f_0(980)$ and $a_0(980)$ as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the $J/\psi \rightarrow K^+ K^- f_0(980)(a_0(980))$ decays are of the order of $10^{-5}$, accessible in present facilities, and we argue that their observation should provide relevant information concerning the nature of the low-lying scalar mesons.Comment: 12 pages, 8 figures, published in EPJ