Studies on the emission from the receding jet of GRBXin Wang, Y. F. Huang, and S. W. KongDepartment of Astronomy, Nanjing University, ChinaA&A submitted (arXiv:0903.3119v2)

ContentsIntroductionModelNumerical ResultsComparisonsConclusion

IntroductionThe standard fireball-shock model

Beaming effect: achromatic break in afterglow LCs, polarization, energy crisis, orphan afterglowMszros 03

ModelWe use the convenient generic dynamical model advanced by Huang et al (2000).The physical picture is that the homogeneous double-sided jet expands into a homogeneous interstellar medium (ISM).Dynamics:

Radiation: synchrotron radiation & self-absorption

Numerical ResultsDynamic evolution of the receding jetTotal equal arrival time surface (EATS)The overall light curves (LCs) considering the contribution from the receding jet componentThe effects of various parameters on the receding jet componentDifferent characteristics for the twin jetsFirstly, we assume the twin jets have the same characteristics. The parameters of the standard condition are defined as follows:

Dynamic evolution of the receding jetjet break time is determined by in a rather long observers time (t100 d), of the receding jet remains almost constant

Total equal arrival time surface (EATS)Due to that speed of light is not infinite, photons received at an observer time tobs are emitted from a distorted ellipsoid not simultaneously, which is determined byEATS for the receding jet branch has much smaller typical radius much flatter curvaturemuch smaller areaas compared with those for the forward jet branch at the same observer time.

The overall light curves

The effects of various parametersAll 8.46 GHz LCs

Different characteristics for twin jets

Comparisonswith theoretical derivationswith other numerical resultsOur results are consistent with other colleagues.

ConclusionIt is found that the contribution from the receding jet is quite weak and only manifests as a plateau (~0.1 for 8.46 GHz) typically, which is hard to detect.At lower frequency, the relative intensity of the receding jet component becomes stronger, as compared with the peak flux of the forward jet component.Generally, our result is consistent with Zhang & MacFadyens and Li & Songs. However the subtle difference between our numerical results and Li & Songs analytical derivations is ascribed to the EATS effect and the deceleration of the external shock.Contribution from the receding jet can be greatly enhanced if the circum-burst environment is very dense and/or the micro-physics parameters of receding jet is different and/or the burst has a low redshift. Thus we suggest that nearby GRBs (z 0.1) be good candidates for observations.

Thanks for your patience!