Observations Of Early Reverse Shock Emission And Constraints On Jet Radiation Region Properties Of Gamma-ray Bursts

It is generally believed that gamma-ray bursts(GRBs)are the most luminous explosive events,which are originated from the death of massive stars or mergers of compact binaries in the universe.Prompt gamma-ray emission and their multi-wavelength afterglows are produced by an ultra-relativistic jet powered by stellar black holes(BHs)or rotating strange stars and neutron stars.Early optical afterglows could play an unique role in studying the fireball properties and the circum medium.We report observations of bright prompt optical and reverse shock(RS)optical emission of GRBs 140512A,161017A,160625B and analyze their multi-wavelength data.Our optical observations of GRB 140512A were made with the 0.8 m TNT telescope.It is found that our first optical detection(R=13.09 mag)may be the prompt optical emission.Our empirical fit to the afterglow lightcurves indicates that the optical afterglow lightcurve is consistent with predictions of the RS and forward shock(FS)emission of external shock models.We fit the lightcurves with standard external models,and derive the physical properties of the outflow.It is found that the ratio RB = ?B/?b,f = 8187,indicating a high magnetization degree in the RS region.Measuring the relative radiation efficiency with Re =?e,r/?e,f,we have Re = 0.02,implying that the radiation efficiency of the RS is much lower than that in FS.Besides,the ratio RB of GRBs 161017A and 160625B is 16 and 222,respectively.In addition,we also show that the RB values of GRBs 990123,090102,and 130427A are similar to that of GRB 140512A and their apparent difference may be mainly attributed to the difference of the jet kinetic energy,initial Lorentz factor(?0),and medium density among them.High energy photon radiations of GRBs and active galactic nuclei(AGNs)are dominated by their jet radiations.It was suggested that relativistic jets powered by different mass-scale black holes may share the same physical laws.A tight relation among the peak luminosity(Liso,z),the peak photon energy(Ep,z)in the vfv spectrum,and the initial Lorentz factor is found for GRBs.With samples of GeV-TeV selected BL Lacs,flat spectrum radio quasars(FSRQs),and narrow-line Seyfert 1(NLS1)galaxies,we show that the AGNs jet radiation does not follow the same Lsynr(Esyn,z,?)relations as the Lp,zr(Ep,Z,?0)relation of GRBs.Moreover,the dependence of the luminosity on the Lorentz factor is dramatically different among these sources.This may be attributed to the difference of jet geometry and continuous/episodic jet as well as jet composition.