It is believed that orphan afterglow searches can help to measure the beaming angle in gamma-ray bursts (GRBs). Great expectations have been put on t

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.

We numerically investigate optical afterglows from two-component jets under various configurations. Generally, the light curve is characterized by a rapid rebrightening when the observer is off-axis with respect to the narrow component, with the amplitude and peak time depending on detailed parameters. We further show that the optical afterglow of XRF 030723, especially its notable and rapid rebrightening, can be well explained by a typical two-component jet. This X-ray flash, together with GRB 030329, strongly hints toward the two-component jet model as a unified picture for X-ray flashes and gamma-ray bursts. With a narrow but ultrarelativistic inner outflow and a wide but less energetic outer ejecta, a two-component jet will be observed as a typical gamma-ray burst if our line of sight is within the angular scope of the narrow outflow. Otherwise, if the line of sight is within or slightly beyond the cone of the wide component, an X-ray flash will be detected.

The interaction of a relativistic fireball with its ambient medium is described through two shocks: a reverse shock that propagates into the fireball