Well-sampled optical light curves of 50 gamma-ray bursts (GRBs) with plateau features are compiled from the literature. By empirical fitting, we obtained the parameters of the optical plateaus, such as the decay slopes (α ₁ and α ₂), the break times (T _b), and the corresponding optical fluxes (F _b) at the break times. The break time of optical plateaus ranges from tens of seconds to 10⁶ s, with a typical value of about 10⁴ s. We have calculated the break luminosity, and it mainly ranges from 10⁴⁴ erg s⁻¹ to 10⁴⁷ erg s⁻¹, which is generally two or three orders of magnitude less than the corresponding break luminosity of the X-ray afterglow plateaus. We reanalyzed the optical plateaus and also found that a significantly tighter correlation exists when we added the isotropic equivalent energy of GRBs E _γ,iso into the L _b,z–T _b,z relation. The best-fit correlation is obtained to be L b , z ∝ T b , z − 0.9 E γ , iso 0.4 . We next explored the possible correlations among L _b,z, T _b,z and E _p,i, and found there is also a tight correlation between them, which takes the form of L b , z ∝ T b , z − 0.9 E p , i 0.5 . We argue that these two tight L _b,z–T _b,z–E _γ,iso and L _b,z–T _b,z–E _p,i correlations are more physical, and it may be directly related to the radiation physics of GRBs. The tight correlations can possibly be used as standard candles.

The Dark Energy Spectroscopic Instrument (DESI) collaboration recently released the first-year data of baryon acoustic oscillations (BAOs). Based on the five different tracers, the cosmological constraint shows a hint of deviation from the standard ΛCDM model. In this Letter, we combine the DESI BAOs with other cosmic probes to constrain the evolution of the Hubble constant as a function of redshift in the flat ΛCDM model. The nonparametric method is used to estimate the value of the Hubble constant at different redshift bins. The correlations among different bins are removed by diagonalizing the covariance matrix. The joint data sample demonstrates a decreasing trend of the Hubble constant with a significance of 6.4σ, which can naturally resolve the Hubble tension. To avoid statistical effects caused by the binning methods, we tested three other different binning methods and also found a decreasing trend. It may be due to dynamical dark energy or modified gravity.

It is generally supposed that a transition from the normal decay phase (decay slope ∼−1) to a steeper phase (decay slope ∼−2) could be suggested as a jet break. The jet opening angle θ _jet is then calculated from the jet break time of the afterglow light curve. This allows the derivation of the collimation-corrected energy E _jet of those gamma-ray bursts (GRBs). We extensively searched for the GRBs with jet break features from multiwavelength afterglow light curves, and 138 GRBs with significant breaks were collected. The jet break times of those GRBs mainly range from 1000 to 10⁶ s, and the distribution of the collimation-corrected energy E _jet peaks at ∼10⁵⁰ erg. We also confirmed the E _γ,iso−E _p,i, E _jet−E _p,i and E _γ,iso−θ _jet relations, and found E _γ,iso−T _j,z−E _p,i relation remains tight with more multiwavelength data. This tight E _γ,iso−T _j,z−E _p,i relation is also conformed by different groups of our selected GRBs in the paper. In addition, another two new and tighter correlations among E _jet−T _j,z−E _p,i are well confirmed for different circumburst mediums in this paper. We suggest that those tight three-parameter correlations are more physical, and could be widely applied to constrain the cosmological parameters.

The reverse shock (RS) model is generally introduced to interpret the optical afterglows with the rapid rising and decaying, such as the early optical afterglow of GRB 990123 (which is also called the optical flash). In this paper, we collected 11 gamma-ray burst (GRB) early optical afterglows, which have signatures of dominant RS emission. Since the temporal slopes of the optical flashes are determined by both the medium density distribution index k and the electron spectral index p, we apply the RS model of the thin shell case to the optical flashes and determine the ambient medium of the progenitors. We find that the k value is in the range of 0–1.5. The k value in this paper is consistent with the result in Yi et al., where the forward shock model was applied to some onset bumps. However, the method adopted in this paper is only applicable to GRB afterglows with significant sharp rising and decaying RS emission. Our results indicate that the RS model can also be applied to confirm the circumburst medium, further implying that GRBs may have diverse circumburst media.

Distinct X-ray plateau and flare phases have been observed in the afterglows of gamma-ray bursts (GRBs), and most of them should be related to central engine activities. In this paper, we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares. There are 51 GRBs that overlap in the two selected samples. We analyze the distributions of the proportions of the plateau energy E _plateau and the flare energy E flare relative to the isotropic prompt emission energy E _γ,iso. The results indicate that they well meet the Gaussian distributions and the medians of the logarithmic ratios are ∼−0.96 and −1.39 in the two cases. Moreover, strong positive correlations between E _plateau (or E flare ) and E _γ,iso with slopes of ∼0.95 (or ∼0.80) are presented. For the overlapping sample, the slope is ∼0.80. We argue that most of X-ray plateaus and flares might have the same physical origin but appear with different features because of the different circumstances and radiation mechanisms. We also test the applicabilities of two models, i.e., black holes surrounded by fractured hyperaccretion disks and millisecond magnetars, on the origins of X-ray plateaus and flares.