2018ApJ...863...50S

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 (α₁ and α₂), 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^–0.9E_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^–0.9E_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.