Optical Emission Components of Gamma-Ray Burst Phenomenon

Enwei LiangGXU-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

Based on following papers:1. Liang et al. 2010, Constraining Gamma-ray Burst Initial Lor

entz Factor with the Afterglow Onset Feature and Discovery of a Tight Γ0-E γ,iso Correlation 2010, ApJ, 725, 2209

2. Li et al. 2012, A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component, arXiv1203.2332

3. Liang et al. 2012 A Comprehensive Study of Gamma-Ray Burst Optical Emission: II. Afterglow Onset and Late Re-Brightening Components, 2012, in preparation

Outlines Motivation Sample and a Synthetic Lightcurve of Optical Emis

sion Late Flares Implications for Global Evolution of

the GRB Central Engine Early Shallow Decay Segment Implications for E

nergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Implic

ations for the properties of GRB fireball and Environment

Summary

Outlines Motivation Sample and a Synthetic Lightcurve of Optical EmisSample and a Synthetic Lightcurve of Optical Emis

sionsion Late Flares Late Flares Implications for Global Evolution of Implications for Global Evolution of

the GRB Central Enginethe GRB Central Engine Early Shallow Decay SegmentEarly Shallow Decay Segment Implications for E Implications for E

nergy Injection and the Nature of the GRB CEnergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Early Afterglow and Late-Rebrightening Implic Implic

ations for the properties of GRB fireball and Envirations for the properties of GRB fireball and Environment onment

Summary Summary

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 Motivation Sample and a Synthetic Lightcurve of Optical Emis

sion Late Flares Late Flares Implications for Global Evolution of Implications for Global Evolution of

the GRB Central Enginethe GRB Central Engine Early Shallow Decay SegmentEarly Shallow Decay Segment Implications for E Implications for E

nergy Injection and the Nature of the GRB CEnergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Early Afterglow and Late-Rebrightening Implic Implic

ations for the properties of GRB fireball and Envirations for the properties of GRB fireball and Environment onment

Summary Summary

1. Sample and a Synthetic Lightcurve1. Sample and a Synthetic Lightcurve

Sample: Full sample of GRBs with optical afterglow detection from 1

997-2012 230 GRBs included 146 well-sampled LCs for our analysis. Most of them were o

bserved in the R-band. Corrections:

k-correction, Galactic extinction (No correction for host galaxy extinction

)

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Component Decomposing with Empirical Fits

(I)(I)Single PLSingle PL

(II) Smooth (II) Smooth BKPL:BKPL:

(III) Triple PL(III) Triple PLStrategy of out LC fititng: Strategy of out LC fititng:

Adding components to improve the LC fits. Criterion: Adding components to improve the LC fits. Criterion:

(1)Reduced χ(1)Reduced χ22~ 1 and adding one more component does not ~ 1 and adding one more component does not significantly improve the fits significantly improve the fits Accepted; Accepted;

(2) Reduced χ(2) Reduced χ22 is much larger than 1, but add one more com is much larger than 1, but add one more component cannot significantly improve the fit ponent cannot significantly improve the fit Accepted Accepted

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Examples of our fits with extremely small or large reduced χχ2

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

2. 2. A synthesis Lightcurves of Optical EmiA synthesis Lightcurves of Optical Emission from GRB phenomenonssion from GRB phenomenon

Zhang et al. Zhang et al. 20062006

XRT LCsXRT LCs

Shallow decay: Shallow decay: α<3β/2α<3β/2

Jet-like decay: Jet-like decay: α>2β+1 α>2β+1

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Outlines Motivation Sample and a Synthetic Lightcurve of Optical Emis

sion Late Flares Implications for Global Evolution of

the GRB Central Engine Early Shallow Decay SegmentEarly Shallow Decay Segment Implications for E Implications for E

nergy Injection and the Nature of the GRB CEnergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Early Afterglow and Late-Rebrightening Implic Implic

ations for the properties of GRB fireball and Envirations for the properties of GRB fireball and Environment onment

Summary Summary

3. FlaresDefinition: 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)

Flares: Temporal Evolution

Width as a function of tp: shWidth as a function of tp: sharing the same relation with aring the same relation with single pulse GRBs and X-ray single pulse GRBs and X-ray flaresflares

Anti-correlation between LAnti-correlation between Lp and tp p and tp Being similar to Being similar to that of the X-ray flaresthat of the X-ray flares

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Peaking later tends to be wider and dimmer

15.015.1 pp tL

Flares: Temporal Evolution

Width as a function of tp: shWidth as a function of tp: sharing the same relation with aring the same relation with single pulse GRBs and X-ray single pulse GRBs and X-ray flaresflares

Anti-correlation between LAnti-correlation between Lp and tp p and tp Being similar to Being similar to that of the X-ray flaresthat of the X-ray flares

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

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 )

Outlines Motivation Sample and a Synthetic Lightcurve of Optical Emis

sion Late Flares Implications for Global Evolution of

the GRB Central Engine Early Shallow Decay Segment Implications for E

nergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Early Afterglow and Late-Rebrightening Implic Implic

ations for the properties of GRB fireball and Envirations for the properties of GRB fireball and Environment onment

Summary Summary

4. Shallow decay segment

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Definition: α<3β/2 α<3β/2 （ （ υυmm<υ<υOO<υ<υcc ））

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. (arXiv1203.2332)

Break time and Break Luminosity

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

•tb is achromatic, but tentative correlated.

Typical break ~ 104 s

76.0 bb tL

X-rayX-ray

Opt.Opt.

Break time and Break Luminosity

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

•tb is achromatic, but tentative correlated.

Typical break ~ 104 s

76.0 bb tL

X-rayX-ray

Opt.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: For a BH-torus system:

The injection wind may bThe injection wind may be driven by neutrino annihile driven by neutrino annihilation or the Blandford-Znajeation or the Blandford-Znajek mechanism: k mechanism:

(Kumar et al. 200(Kumar et al. 2008)8)

For a spinning down magnetFor a spinning down magnetar ar

q would be 0 or 2q would be 0 or 2

Can the shallow decay segment be a probe for the nature of GRB central engine?

qtLL 0

3.0 tM f

If it is due to long-If it is due to long-lasting energy lasting energy injection, injection,

Li, Liang et al. 2012, ApJ, sub. (arXiv1203.2332)

Outlines Motivation Sample and a Synthetic Lightcurve of Optical Emis

sion Late Flares Implications for Global Evolution of

the GRB Central Engine Early Shallow Decay Segment Implications for E

nergy Injection and the Nature of the GRB CE Early Afterglow and Late-Rebrightening Implic

ations for the properties of GRB fireball and Environment

Summary Summary

5. Afterglow Onset and Late Re-brightening

(1) Detection rate: 42/1(1) Detection rate: 42/146 (2)Smooth, less of fl46 (2)Smooth, less of flaresares

(3)No Association with (3)No Association with X-rays for most GRBsX-rays for most GRBs

Liang et al. 2010, ApJLiang et al. 2010, ApJ

(1) Detection rate: (1) Detection rate: 30/14630/146

(2)Similar to the (2)Similar to the onset humpsonset humps

More Examples……

Liang et al. 2010, Liang et al. 2010, ApJ ApJ

More Examples of late rebrightening

Separation of the humps are getting Separation of the humps are getting largerlarger

Distributions of the Slopes

Liang, Li, Gao, et al. 2012 ， in prep.

Distribution of the afterglow peak time

Liang, Li, Gao, et al. 2012 ， in prep.

Temporal Evolution

Width vs peak time Lp vs EisoLp vs peak time

RB

RB

RBOnset Onset

Onset

Liang, Li, Gao, et al. 2012 ， in prep.

Relation between Afterglow and Eiso

Liang et al. 2010, Liang et al. 2010, ApJ ApJ

Larger Eiso Larger Eiso Earlier & brighter onset bump Earlier & brighter onset bump

Initial Lorentz Factors and its tight Relation to Eiso

(Sari & Piran 19(Sari & Piran 1999)99)

Liang et al. 2010, Liang et al. 2010, ApJ 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. 2012 ， in prep.

Future…

GRB observation strategyGRB observation strategy

GroundGround

SpaceSpace

GWACGWAC

GFTs GFTs (g, r, i, J, H)(g, r, i, J, H)

TT00 +1 min +1 min

1-2 m robotic telescopes1-2 m robotic telescopes

GRB trigger provided by GRB trigger provided by ECLAIRsECLAIRs at time T at time T00

VTVT (V & R band photometry) (V & R band photometry)MXTMXT (Soft X-ray photometry) (Soft X-ray photometry)

TT00 + 5 min + 5 min

Multi messenger follow-upMulti messenger follow-up

60-cm 60-cm RobotiRobotic Telesc Teles

co co

From JianyanFrom Jianyan

Multi-wavelength capabilities of SVOM Multi-wavelength capabilities of SVOM

102 103 104 105101-5 0

1022

1020

1016

1018

1014

1015

1014

Time (s)

Log. scale

Time (m)

Lin. scale

Fre

qu

ency

(H

z)F

req

uen

cy (

Hz)

Space

Ground

Slew

GRM

ECLAIRs MXT

VT

GWAC

F-GFT

C-GFT

60-cm 60-cm RobotiRobotic Telesc Teles

co co

From JianyanFrom Jianyan

Summary Long-lasting internal plateau, flare, and re-brightening are reveal

ed from current sample. The detection rate of optical flares are much lower than X-ray flar

es. 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.

Thanks