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Global Properties of X-ray Afterglows Observed with XRT

Global Properties of X-ray Afterglows Observed with XRT. ENWEI LIANG （梁恩维） University of Guangxi, Nanning astro.gxu.edu.cn Nanjing 2008.06.23. University of Guangxi. Collaborators. BING ZHANG (UNLV) BINBIN ZHANG (UNLV) Judith L. Racusin ( PENN. STATE UNIVERSITY )

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Global Properties of X-ray Afterglows Observed with XRT

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  1. Global Properties of X-ray Afterglows Observed with XRT ENWEI LIANG（梁恩维） University of Guangxi, Nanning astro.gxu.edu.cn Nanjing 2008.06.23 University of Guangxi

  2. Collaborators • BING ZHANG (UNLV) • BINBIN ZHANG (UNLV) • Judith L. Racusin (PENN. STATE UNIVERSITY) • DAVE BURROWS (PENN. STATE UNIVERSITY)

  3. Outline • General features of Swift/XRT LCs • Our Data Reduction Code • Results of our comprehensive analysis • Shallow decay segment • Normal decay segment • Jet-like decay segment • Summary

  4. Non-Canonical XRT LC • X-ray Flares • Canonical XRT LC Guido’s Talk BinBin’s talk This talk 1.General features of XRT LCs(see Dave’s talk this morning) • ~ 90 % Swift GRBs have X-ray afterglow detection. Burrows et al. 2005; Zhang et al. 2006; Nousek et al. 2006; O’Brien et al. 2006 Lv et al. 2008( in preparation)

  5. 2.Our Data Reduction Code • Setting up two data processing servers at UNLV & GXU • Full Function for Swift BAT & XRT data process: • automatically download and maintain Swift data • Automatically make pileup correction and exposure correction • Extract the BAT and XRT lightcurves at any user-specified temporal and spectral regimes • Automatically extract the BAT and XRT spectra and fit with Xspec • Output eps figures for publication • Scripts and data are available at : • http://grb.physics.unlv.edu/ ( @ UNLV) • http://astro.gxu.edu.cn/web/ ( @ GXU)

  6. 3.What we did: A comprehensive analysis • Data: two-year XRT observations. • Temporal analysis • Spectral analysis • Data vs Fireball model: Challenges to conventional GRB models

  7. 4. ShallowNormal decay segments:(1)Data & Analysis method • LC fitting model: Broken power law • Sample selection Criterion: • No significant flares in the afterglow phase (reduced chi^2<2). • Both the shallow and normal decay segments are bright enough to make spectral analysis. • Sample: 52 bursts from 2 year XRT data (179) Zhang et al. 2006 (Liang et al. 2007, ApJ)

  8. 4. ShallowNormal decay segments:(2)Distributions of Characteristcs Break time X-ray fluence Ph. Index Decay slope (Liang et al. 2007, ApJ)

  9. Duration Ph. Index fluence 4. ShallowNormal decay segments:(3) Correlations with Prompt Emisison Energy (Liang et al. 2007, ApJ)

  10. 4. ShallowNormal decay segments: (4)spectral evolution! (Liang et al. 2007, ApJ)

  11. 4. ShallowNormal decay segments: (5) Data vs closure relations • Most of the normal decay segments are roughly consistent with the closure relationsEnergy Injection? • Four cases are notInternal origin?. (Liang et al. 2007, ApJ)

  12. Eiso∝tb,opt-1.2 4. ShallowNormal decay segments: (6) Energy injection? Liang-Zhang relation (Liang et al. 2007)

  13. 4. ShallowNormal decay segments: (6) X-Ray vs Optical (a) Achromatic! (Liang et al. 2007)

  14. 4. ShallowNormal decay segments: (6) X-Ray vs Optical (b) Continuous energy injection? (Rees & Meszaros 1998; Dai & Lu 1998; Panaitescu et al. 1998; Sari & Meszaros 2000 ; Zhang Meszaros et al. 2001; Wang & Dai 2001; Dai 2004; Granot & Kumar 2006; Panaitescu 2007; Yu \& Dai 2007; Liang et al. 2007b) Delayed onset of the afterglow emission? (Kobayashi \& Zhang 2007) Off-beam jet effect? (Toma et al. 2006; Eichler & Granot 2006) pre-cursor?(Ioka et al. 2006); Two-component jet ? (Granot et al. 2006;Jin et al. 2007), Varying microphysics parameter?(Ioka et al. 2006; Panaitescu et al. 2006b; Fan & Piran 2006; Granot et al. 2006) Reflection?(Panaitescu et al. ; Shen et al. 2007) Dust scattering of prompt X-rays ?(Shao & Dai 2007) Emission from a long-lived reverse shock? (Uhm & Beloborodov 2007; Genet, Daigne & Mochkovitch 2007) Long –lasting, steady central engine emission? (Troja et al. 2007; Liang et al. 2007a) Late prompt emission?(Ghisellini et al. 2007) Chromatic! A Great issue for the energy injection scenario! (Liang et al. 2007)

  15. 5. NormalJet-like decay segments:(1) Data & Sample • LC fitting models: • Smoothed triple power law (STPL) • Smoothed broken power law • Single power law 2. Sample selection: • Criterion: No significant flares in the afterglow phase (reduced Chi2<2). • X-ray sample: 103 bursts from 2 year XRT data (179) • Optical data: from literatures (57 bursts) Zhang et al. 2006 (Liang et al. 2008, ApJ)

  16. (Liang et al. 2008, ApJ)

  17. (Liang et al. 2008, ApJ)

  18. 5. NormalJet-like decay segments:(2) Grading jet break candidates (Progressively rigorous grades) • Detection fraction of the jet break candidates in XRT lightcurves is much lower than that in optical band. • None of the breaks can be graded as “Platinum”! Liang et al. 2008 (see also Judith L. Racusin et al. 2007; Panaintescu 2007)

  19. (Liang et al. 2008, ApJ)

  20. ISM Wind Post-Break Post-Break Pre-Break Pre-Break 5. NormalJet-like decay segments:(3) Data vs Closure relations (X-rays) Liang et al. 2008, ApJ (see also Panaitescu 2007, MNRAS)

  21. Post-Break Post-Break Pre-Break Pre-Break ISM Wind 5. NormalJet-like decay segments:(4) Data vs Closure relations (opt) Liang et al. 2008, ApJ

  22. Limits Pre-Swift detection Swift Liang et al. 2008, ApJ 5. NormalJet-like decay segments:(5) Jet Collimation & Kinetic Energetics Assuming: ``Silver'' or ``Gold'' jet break candidates are jet breaks+ Following the standard forward shock model t Constraining jet collimation and kinetic energy

  23. 5. NormalJet-like decay segments:(6)Achromatic vs. chromatic 13 bursts have good temporal coverage in both X-ray and optical bands: achromatic : chromatic =6:7 Liang et al. 2008

  24. 5. NormalJet-like decay segments:(6)Achromatic vs. chromatic • Detection Fraction: (“silver” and “gold”) X-ray: 27/103 optical: 23/57 • Break time and break significance X-rays Opt. X-rays Opt. Liang et al. 2008

  25. X-rays & Opt.: from the same component? One should be very cautious in claiming a jet break!! Chromatic breaks! Challenge to the jet models!

  26. Summary • No significant spectral evolution is observed in the afterglow phase. • The normal decay phase is roughly consistent with external-shock models, with only four significant outliers ( 060413, 060522, 060607A, & 070110). • The properties of the shallow decaysegments are also favor the scenario of the refreshed shocks, but a considerable fraction of shallow-to-normal breaks are chromatic, raising an issue of this scenario. • No textbook version of jet break is found in our sample. Candidates to various degrees are identified by relaxing one or more requirements, but the break time is generally chromatic, raising concerns about interpreting the breaks as jet breaks. • Assuming that the candidates are jet breaks, the EK,j distribution is much scattered than the pre-Swift sample。

  27. Thanks!

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