Optical Emission Components of Gamma-Ray Burst Phenomenon

1. Optical Emission Components of Gamma-Ray Burst Phenomenon Enwei Liang GXU-NAOC Center for Astrophys. & Space Sci. Co-authors: Liang Li (GXU), Shuangxi Yi (NJU), QingwenTang(GXU), Bing Zhang (UNLV) Gamma Ray Bursts in the Era of Rapid Follow-up 18-22 June 2012, Liverpool, UK

2. Based on following papers: • Liang et al. 2010, Constraining Gamma-ray Burst Initial Lorentz Factor with the Afterglow Onset Feature and Discovery of a Tight Γ0-E γ,iso Correlation 2010, ApJ, 725, 2209 • Li et al. 2012, A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component, arXiv1203.2332 • Liang et al. 2012 A Comprehensive Study of Gamma-Ray Burst Optical Emission: II. Afterglow Onset and Late Re-Brightening Components, 2012, in preparation

3. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

4. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

5. Motivation • Theoretical models predict various emission components  Mixing of different components cannot make sense for statistics. • Extract various Emission Components from the data by empirical fit  for statistics, probing the properties of CE, GRB fireball, further theoretically modeling,…. • How about the relations between X-ray and optical emission?

6. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

7. 1. Sample and a Synthetic Lightcurve • Sample: • Full sample of GRBs with optical afterglow detection from 1997-2012 • 230 GRBs included • 146 well-sampled LCs for our analysis. Most of them were observed in the R-band. • Corrections: • k-correction, • Galactic extinction (No correction for host galaxy extinction ) Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

8. Single PL • (II) Smooth BKPL: • (III) Triple PL • Component Decomposing with Empirical Fits Strategy of out LC fititng: Adding components to improve the LC fits. Criterion: (1)Reduced χ2~ 1 and adding one more component does not significantly improve the fits  Accepted; (2) Reduced χ2 is much larger than 1, but add one more component cannot significantly improve the fit  Accepted Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

9. Examples of our fits with extremely small or large reduced χ2 Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

10. 2. A synthesis Lightcurves of Optical Emission from GRB phenomenon XRT LCs Zhang et al. 2006 Shallow decay: α<3β/2 Jet-like decay: α>2β+1 Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

11. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

12. 3. Flares Definition: rising and decaying slopes both are steeper than 2. Detection Rate: 19/146 Much lower than X-ray flares No associated X-ray flares were detected for most GRBs, except for GRBs 060926, 070311, and 071010A in our sample. Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

13. Flares: Temporal Evolution Peaking later tends to be wider and dimmer Width as a function of tp: sharing the same relation with single pulse GRBs and X-ray flares Anti-correlation between Lp and tp  Being similar to that of the X-ray flares Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

14. Flares: Temporal Evolution Peaking later tends to be wider and dimmer • Prompt gamma-ray Early X-ray flares Late optical flares: Global evolution of the GRB central engine activity • The Temporal Evolution of Lp is consistent with the evolution of the accretion rate predicted by some models (~ t-1.2-1.25 Cannizzo et al. 1990, Frank et al. 2002 ) Width as a function of tp: sharing the same relation with single pulse GRBs and X-ray flares Anti-correlation between Lp and tp  Being similar to that of the X-ray flares Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

15. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

16. 4. Shallow decay segment Definition: α<3β/2 （ υm<υO<υc） Detection Rate: 42/146 ，Comparable to that in the X-ray band. Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

17. Decay slopes • The decay slope of about 1/3 of the shallow decay segments transit to even steeper than -2. Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

18. Break time and Break Luminosity X-ray Opt. Typical break ~ 104 s • tb is achromatic, but tentative correlated. Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

19. Break time and Break Luminosity X-ray Opt. Note: Only a small fraction of GRBs have a break in both the optical and X-ray bands! (18/146 for our sample)! Typical break ~ 104 s • tb is achromatic, but tentative correlated. Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

20. Can the shallow decay segment be a probe for the nature of GRB central engine? If it is due to long-lasting energy injection, For a BH-torus system: The injection wind may be driven by neutrino annihilation or the Blandford-Znajek mechanism: (Kumar et al. 2008) For a spinning down magnetar q would be 0 or 2 Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

21. Outlines • Motivation • Sample and a Synthetic Lightcurve of Optical Emission • Late Flares  Implications for Global Evolution of the GRB Central Engine • Early Shallow Decay Segment Implications for Energy Injection and the Nature of the GRB CE • Early Afterglow and Late-Rebrightening  Implications for the properties of GRB fireball and Environment • Summary

22. 5. Afterglow Onset and Late Re-brightening (1) Detection rate: 42/146 (2)Smooth, less of flares (3)No Association with X-rays for most GRBs (1) Detection rate: 30/146 (2)Similar to the onset humps Liang et al. 2010, ApJ

23. More Examples…… Liang et al. 2010, ApJ

24. More Examples of late rebrightening Separation of the humps are getting larger

25. Distributions of the Slopes Liang, Li, Gao, et al. 2012， in prep.

26. Distribution of the afterglow peak time Liang, Li, Gao, et al. 2012， in prep.

27. Temporal Evolution Lp vs peak time Width vs peak time Lp vs Eiso Onset RB RB RB Onset Onset Liang, Li, Gao, et al. 2012， in prep.

28. Relation between Afterglow and Eiso Larger Eiso  Earlier & brighter onset bump Liang et al. 2010, ApJ

29. Initial Lorentz Factors and its tight Relation toEiso (Sari & Piran 1999) Liang et al. 2010, ApJ

30. Testing GRB environment with the afterglow onset and late RB humps • Using the onset bump, we infer that the medium profile surrounding GRBs are described as K=0.2~ 1.5, with a typical value of 0.8 Liang, Li, Gao, et al. 2012， in prep.

31. Future…

32. T0 + 5 min VT (V & R band photometry) MXT(Soft X-ray photometry) T0 +1 min GWAC GFTs(g, r, i, J, H) 1-2 m robotic telescopes Multi messenger follow-up GRB observation strategy Space GRB trigger provided by ECLAIRs at time T0 Ground 60-cm Robotic Telesco From Jianyan

33. 1022 Space GRM 1020 ECLAIRs MXT Frequency (Hz) 1018 1016 VT Slew 1014 Ground 1015 GWAC C-GFT Frequency (Hz) F-GFT 1014 -5 0 1 10 102 103 104 105 Time (s) Log. scale Time (m) Lin. scale Multi-wavelength capabilities of SVOM 60-cm Robotic Telesco From Jianyan

34. Summary • Long-lasting internal plateau, flare, and re-brightening are revealed from current sample. • The detection rate of optical flares are much lower than X-ray flares. The global evolution of the prompt gamma-ray, early X-ray flares, and late optical flares may signal global evolution of the GRB central engine activity. The Temporal Evolution of Lp is consistent with the evolution of the accretion rate predicted by some models. • The Detection rate of the shallow decay segment is comparable to X-rays. They may be a probe for the nature of GRB central engine. • A tight correlation between the initial Lorentz factor and Eiso is discovered. Smooth re-brightening is different from the flares. They may be from a distinct jet component. We infer the burst environment with the afterglow onset and late rebrightening and found that the density profile n~ r-0.8.

35. Thanks