A plateau phase in the X-ray afterglow is observed in a significant fraction of gamma-ray bursts (GRBs). Previously, a correlation among three key parameters concerning the plateau phase is found to exist, i.e., the end time of the plateau phase in the GRB rest frame (T _a ), the corresponding X-ray luminosity at the end time (L _X) and the isotropic energy of the prompt GRB (E _γ,iso). In this study, we systematically search through all the Swift GRBs with a plateau phase that occurred between 2005 May and 2018 August. We collect 174 GRBs, with redshifts available for all of them. For the whole sample, the correlation between L _X, T _a , and E _γ,iso is confirmed, with the best-fit relation being . Such an updated three-parameter correlation still supports that the central leftover after GRBs is probably a millisecond magnetar. Note that short GRBs with durations less than 2 s in our sample also follow the same correlation, which hints that the merger production of two neutron stars could be a high-mass magnetar but not necessarily a black hole. Moreover, GRBs with an “internal” plateau (i.e., with a following decay index being generally smaller than −3) also obey this correlation. It further strengthens the idea that the internal plateau is due to the delayed collapse of a high-mass neutron star into a black hole. The updated three-parameter correlation indicates that GRBs with a plateau phase may act as a standard candle for cosmology study.

The low-energy spectra of gamma-ray bursts’ (GRBs) prompt emission are closely related to the energy distribution of electrons, which is further regulated by their cooling processes. We develop a numerical code to calculate the evolution of the electron distribution with given initial parameters, in which three cooling processes (i.e., adiabatic, synchrotron, and inverse Compton cooling) and the effect of a decaying magnetic field are coherently considered. A sequence of results is presented by exploring the plausible parameter space for both the fireball and the Poynting flux–dominated regime. Different cooling patterns for the electrons can be identified, and they are featured by a specific dominant cooling mechanism. Our results show that the hardening of the low-energy spectra can be attributed to the dominance of synchrotron self-Compton cooling within the internal shock model or to decaying synchrotron cooling within the Poynting flux–dominated jet scenario. These two mechanisms can be distinguished by observing the hard low-energy spectra of isolated short pulses in some GRBs. The dominance of adiabatic cooling can also lead to hard low-energy spectra when the ejecta is moving at an extreme relativistic speed. The information from the time-resolved low-energy spectra can help to probe the physical characteristics of the GRB ejecta via our numerical results.

Strange stars (SSs) are compact objects made of deconfined quarks. It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS. Here we suggest that the intriguing repeating fast radio bursts (FRBs) are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion. The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario. Especially, the periodicity is attributed to the modulation of accretion rate through the disk instabilities. To account for a ~16-day periodicity of the repeating FRB source of 180916.J0158+65, a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3 × 10¹⁶ g s⁻¹ is invoked. Our scenario, if favored by future observations, will serve as indirect evidence for the strange quark matter hypothesis.

We perform a series of relativistic magnetohydrodynamic simulations to investigate how a hot magnetic jet propagates within the dynamical ejecta of a binary neutron star merger, focusing on how the jet structure depends on the delay time of jet launching with respect to the merger time, Δt _jet. We find that regardless of the jet-launching delay time, a structured jet with an angle-dependent luminosity and Lorentz factor is always formed after the jet breaks out of the ejecta. On the other hand, the jet-launching delay time has an impact on the jet structure. If the jet-launching delay time is relatively long, e.g., ≥0.5 s, the line-of-sight material has a dominant contribution from the cocoon. On the other hand, for a relatively short jet-launching delay time, the jet penetrates through the ejecta early on and develops an angular structure afterward. The line-of-sight ejecta is dominated by the structured jet itself. We discuss the case of GW170817/GRB 170817A within the framework of both long and short jet-launching delay time. In the future, more observations of gravitational-wave/gamma-ray burst associations can help to differentiate between these two scenarios.