| It is generally believed that almost every long GRBs are associated with the deaths of massive stars.The envelope-stripped Wolf-Rayet(WR)stars are supposed to be progenitors of long-duration GRBs,It is expected that the circum-burst medium has been impacted by the stellar wind created by the progenitors.Since the progenitors and the circum-burst medium are embedded in the interstellar medium(ISM),it can be expected that there would be a transition between stellar wind and ISM.When we processed the optical data of GRBs observed by KAIT telescope,found that GRB 140423A has a special optical light curve.Onset bumps were observed in the early optical light curve,then the optical light curves show steeper to flatter decay with a break at?5000 s,and the optical and X-ray afterglow data exhibit an achromatic behavior.Combining with joint spectral analysis,we expect that optical and X-ray data are in the same regime.We model the optical and X-ray light curves with the standard external shock model by considering the cirum-burst medium which transited from a stellar wind to ISM.A set of best-fitting parameters are derived as follows:log?B =-4.42+1.30-1.30,log ?e=-1.55+0.73+0.58,log EK,iso =54.38+0.87-0.78 erg,log?0=2.54+-0.30+0.28,log A*=0.05-1.11+1.10,X=5.22-2.46+2.60,p=2.4-0.27+0.28,log Rt=17.32-0.70+0.67.We also systematically investigate GRBs whose afterglows show similar properties discovered in the Swift era,finding that:(1)only three GRBs(GRB 050721,GRB 061126,and GRB 071112C)both with X-ray and optical afterglow can be explained by our wind-ISM model.(2)We also systematic analyze the GRBs with Swift/XRT data until 2017,and we found 10 GRBs that can be explained by the wind-ISM model.Fitting results shows that:1.The isotropic kinetic energy EK,iso of these GRBs are about 1052-1054 erg.The index of the synchrotron radiating electron spectrum(p)of these GRBs are about 2.3;2.The jet opening angle of these GRBs are widely larger than 10°;3.The transition time of these GRBs are about 1000-3000 s,and the transition radius of these GRBs are about 1016-1017 cmSN 2012aa is a type Ic supernova(SN).It has special bolometric light curve,and its luminosity is between supernovae and superluminous supernovae.We found that the 56Ni model,the magnetar model,and the SN ejecta interacting with stellar wind circumstellar medium(CSM)model can't explain the special bolometric light curve.We expect that an ejecta-circumstellar-medium interaction model could be the energy sources of SN20122aa.We consider an SN ejecta interacting with multiple dense CSM shells,which may be expelled by the eruptions of the progenitor.Fitting result shows the Multi-CSM model can explain the special bolometric light curve of SN 2012aa well.We derived the parameters are:Mej,1=34.89-6.19+2.91 M(?),Mej,2=36.54 M(?),MCSM,1 =1.65+-0.03+0.02 M(?),MCSM,2=15.35-0.49+041 M(?),?CSM,in,1=4.00-0.10+0.10×10-13 g cm-3,?CSM,in,2=0.10-0.00+0.01×10-13 g cm-3,rin,1=4.96-0.05+0.03×1014cm,Rin,2=63.21×1014cm,?1=0.98-0.01+0.01,?2=0.10-0.00+0.000,t shift,1=8.29-0.12+0.12 day,tsthift,2=67.43-1.30+1.67 day.By fitting the light curves,we found that the mass-loss rate of the wind is comparable to previous results. |
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