Studies on the emission from the receding jet of GRB

1. Studies on the emission from the receding jet of GRB Xin Wang, Y. F. Huang, and S. W. Kong Department of Astronomy, Nanjing University, China A&A submitted (arXiv:0903.3119v2)

2. Contents • Introduction • Model • Numerical Results • Comparisons • Conclusion

3. >1016 cm ~1013 cm X O Detailed numerical investigation on the counter-jet emission is still missing Introduction Mészáros 03 • The standard fireball-shock model • Beaming effect: achromatic break in afterglow LCs, polarization, energy crisis, orphan afterglow

4. Model • We 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

5. Numerical Results Firstly, we assume the twin jets have the same characteristics. The parameters of the “standard” condition are defined as follows: • Dynamic evolution of the receding jet • Total equal arrival time surface (EATS) • The overall light curves (LCs) considering the contribution from the receding jet component • The effects of various parameters on the receding jet component • Different characteristics for the twin jets

6. the emission from the receding jet will be very weak in this period, since it is highly beamed backwardly. Dynamic evolution of the receding jet jet break time is determined by in a rather long observer’s time (t～100 d), γof the receding jet remains almost constant

7. 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 by • EATS for the receding jet branch has • much smaller typical radius • much flatter curvature • much smaller area • as compared with those for the forward jet branch at the same observer time.

8. (c) (d) LCs of the double-sided jet with two parameters altered compared with the “standard” condition, i.e. n=1000/cm3 and z=0.1 (dL=454.8 Mpc). The overall light curves

9. The effects of various parameters All 8.46 GHz LCs

10. 8.46GHz LCs. In each panel, the solid line is plotted under the “standard” condition, i.e., the parameters are completely the same for the twin jets (but we have evaluated as 0.01 and as 10-4 here). For other LCs, one or two parameters are changed for the receding jet only. Different characteristics for twin jets

11. Li & Song (2004) Zhang & MacFadyen (2009) Granot & Loeb (2003) Comparisons • with theoretical derivations • with other numerical results Our results are consistent with other colleagues’.

12. Conclusion • It 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 & MacFadyen’s and Li & Song’s. However the subtle difference between our numerical results and Li & Song’s 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.

13. Thanks for your patience!