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 June 2012, Liverpool, UK

Based on following papers: 1. 1.Liang et al. 2010, Constraining Gamma-ray Burst Initial Lorentz Factor with the Afterglow Onset Feature and Discovery of a Tight Γ 0 -E γ,iso Correlation 2010, ApJ, 725, Li et al. 2012, A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component, arXiv Liang et al A Comprehensive Study of Gamma-Ray Burst Optical Emission: II. Afterglow Onset and Late Re- Brightening Components, 2012, in preparation

Outlines

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?

Outlines

1. Sample and a Synthetic Lightcurve Sample:  Full sample of GRBs with optical afterglow detection from  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. (arXiv )

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

χ Examples of our fits with extremely small or large reduced χ 2 Li, Liang et al. 2012, ApJ, sub. (arXiv )

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

Outlines

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 , , and A in our sample. Li, Liang et al. 2012, ApJ, sub. (arXiv )

Flares: Temporal Evolution 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. (arXiv ) Peaking later tends to be wider and dimmer

Flares: Temporal Evolution 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. (arXiv ) 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 Cannizzo et al. 1990, Frank et al )

Outlines

4. Shallow decay segment Li, Liang et al. 2012, ApJ, sub. (arXiv ) α<3β/2 （ υ m <υ O <υ c ） Definition: α<3β/2 （ υ m <υ O <υ c ） Detection Rate: 42/146 ， Comparable to that in the X-ray band.

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. (arXiv )

Break time and Break Luminosity Li, Liang et al. 2012, ApJ, sub. (arXiv ) t b is achromatic, but tentative correlated. Typical break ~ 10 4 s X-ray Opt.

Break time and Break Luminosity Li, Liang et al. 2012, ApJ, sub. (arXiv ) t b is achromatic, but tentative correlated. Typical break ~ 10 4 s 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)!

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

Outlines

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 Liang et al. 2010, ApJ (1) Detection rate: 30/146 (2)Similar to the onset humps

More Examples…… Liang et al. 2010, ApJ

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

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

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

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

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

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

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 ， in prep.

Future …

GRB observation strategy Ground Space GWAC GFTs (g, r, i, J, H) T 0 +1 min 1-2 m robotic telescopes GRB trigger provided by ECLAIRs at time T 0 VT (V & R band photometry) MXT (Soft X-ray photometry) T min Multi messenger follow-up 60-cm Robotic Telesco From Jianyan

Multi-wavelength capabilities of SVOM Time (s) Log. scale Time (m) Lin. scale Frequency (Hz) Space Groun d Slew GRM ECLAIRs MXT VT GWAC F-GFT C-GFT 60-cm Robotic Telesco From Jianyan

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 E iso 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.

Thanks