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X-ray Afterglows of Gamma-ray Bursts

X-ray Afterglows of Gamma-ray Bursts. David Burrows The Pennsylvania State University Swift X-Ray Telescope PI. GRB afterglows. Fireball model: synchrotron emission from power-law distribution of electrons in highly relativistic outflows. Afterglow. LOCAL MEDIUM. Burst. Pre-Burst.

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X-ray Afterglows of Gamma-ray Bursts

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  1. X-ray Afterglows of Gamma-ray Bursts David Burrows The Pennsylvania State University Swift X-Ray Telescope PI

  2. GRB afterglows Fireball model: synchrotron emission from power-law distribution of electrons in highly relativistic outflows Afterglow LOCAL MEDIUM Burst Pre-Burst E ~ 1053 ergs Shock Formation γ, X γ, X T ~ 102 s T = 0 s X, optical, radio R = 3 x 1012 cm T ~ 3 x 103 s R = 106 cm R = 1014 cm Γ ~ 103 T ~ 106 s R = 3 x 1016 cm

  3. 20 November 2004 GRBs and Swift

  4. UVOT BAT BAT XRT UVOT XRT Spacecraft Swift Instruments • Burst Alert Telescope (BAT) • 15-150 keV • 2 sr field of view • CdZnTe detectors • Most sensitive gamma-ray imager ever • Detect ~100 GRBs per year • X-Ray Telescope (XRT) • 0.2-10 keV • Few arcsecond positions • CCD spectroscopy • UV/Optical Telescope (UVOT) • 170 – 650 nm • Sub-arcsec positions • Grism spectroscopy • 6 UV/optical broad-band filters • 22nd mag sensitivity (filtered) • Spacecraft • Autonomous re-pointing, 20 - 75 sec • Onboard and ground triggers All Swift data are immediately public http://swift.gsfc.nasa.gov/sdc/

  5. Short GRB FRED Fast Rise Exponential Decay Short GRB Swift GRBs (> 440 so far) 90% followed up with XRT observations

  6. GRB 060204B GRB 060211A GRB 060306 1e2 1e6 GRB 060413 GRB 060428A GRB 060502A GRB 060510A GRB 060510B GRB 060729 Swift X-ray Afterglows > 370 Prompt X-ray LCs

  7. Key Swift Discoveries GRBs • ~90% of world X-ray afterglows • Complex X-ray lightcurves and flares

  8. VLT GRB 071227 (D’Avanzo et al. 2007) Key Swift Discoveries GRBs • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors

  9. GRB 060614 at z=0.125 (Gal-Yam et al. 2006) Key Swift Discoveries GRBs • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors • Nearby long GRBs with and without SNe • Possible new classes of GRBs

  10. GRB 050730 at z=3.97 (Chen et al. 2005) Key Swift Discoveries GRBs • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors • Nearby long GRBs with and without SNe • Possible new classes of GRBs • Metallicities of star forming regions in galaxies to record high redshift (z=8.2) using GRBs • Includes transitions never before seen z=6.7

  11. t-(2+β) ~ t-3 (Kumar & Panaitescu 2000) Emergence of afterglow Canonical LC: GRB 050315 Vaughan et al. 2005 0 t-5.2 -1.90.9 1 2 3 t-0.4 4 t-0.7 -0.730.11 Zhang et al. 2006, ApJ, 642, 354

  12. X-ray Flares GRB 050730 Burrows et al. 2005, Science, 309, 1833 Romano et al. 2006, A&A, 450, 59 Falcone et al. 2006, ApJ, 641, 1010 Liang et al. 2006, ApJ, 646, 351 Burrows et al. 2006, X-ray Universe (ESA SP-604), 877 Guetta et al. 2007, AIP Conf. Proc., 924, 17 Chincharini et al. 2007, ApJ, 671, 1903 Falcone et al. 2007, ApJ, 671, 1921 Kocevski, Butler, & Bloom 2007, ApJ, 667, 1024 Morris, D. 2008, PhD thesis

  13. X-ray Flares 3x

  14. X-ray Flares • ~ ½ of bursts have X-ray flares • typical time scale ~ hundreds of seconds Power law slope ~ -1.1

  15. Kocevski et al. 2007 Width distribution of flares Flare durations are proportional to time since burst (Chincarini et al.; Kocevski et al.). => Flare models should reproduce this. Chincarini et al. 2007 Chincarini et al., Falcone et al. examined 77 flares in 33 bursts from first full year of XRT operations.

  16. Flare rise and fall times • Mechanisms: • Ambient density fluctuations • Patchy shell • Refreshed shocks • Restarted central engine Kinematically allowed regions for afterglow variability Only a restarted central engine is consistent with all X-ray flares. In context of internal shock model, this probably requires fall-back of material at quite late times. off-axis on-axis Ioka et al. 2005; Chincarini et al. 2007

  17. Flare Mechanisms(D. Morris, PhD thesis, 2008) • Compare each flare to required characteristics of several models • Reverse Shock IC: 1 • Cloud Model I: 0 • Cloud Model II: 3 • Internal Shocks: 11 • Afterglow Onset: 1 • Energy Injection: 3 • Implies IS most likely model for any particular flare, but likely need several models to explain the entire collection of GRB X-ray flares

  18. X-ray Flare Mechanism Internal Shocks? • All of previous points are consistent with internal shocks. • Spectral evolution of flares consistent with spectral evolution of prompt pulses • Burrows et al. (2005, Science, 309, 1833) • Falcone et al. (2005, ApJ, 641, 1010) • Pagani et al. (2006, ApJ, 645, 1613) • Burrows et al. (2007, Phil. Trans. Royal Soc. A., 365, 1213) • Butler & Kocevski (2007, ApJ, 668, 400) • Examination of post-flare decay slopes suggests that “clock” is reset at beginning of each flare • Liang et al. (2006 , ApJ, 646, 351) • Requires late-time activity of central engine => central engine restarts as late at 104 s after burst. Upscattered emission? • Panaitescu (2008, MNRAS, 383, 1143)

  19. GRB 060729 Plateau phase ~ 40 ks Plateau Phase

  20. Plateau Phase • Thought to be energy injection into the external shock, either by • Delayed impacts of slower shocks created at the time of the burst, or • Late-time ejection of relativistic shells from the central engine • Difficult to distinguish between these alternatives in most cases.

  21. The Plateau of GRB 070110 Rapid decline Small flare Plateau ??? t-9 Troja et al. 2007, ApJ, 665, 599

  22. Troja et al. 2007, ApJ, 665, 599 Plateau Phase Comparison with GRB 050904:

  23. Plateau Phase Other recent examples:

  24. Plateau Phase Other recent examples:

  25. Plateau Phase • Drop-offs: • Steep decline cannot be caused in external shock • Requires long-lived central engine activity • Could be explained by magnetar spin-down in some cases

  26. Plateau Phase • Drop-offs: • Steep decline cannot be caused in external shock • Requires long-lived central engine activity • Could be explained by magnetar spin-down in some cases • Other Possibilities: • Recovery from intense photohadronic phase that depletes internal GRB blast wave energy: Dermer (2007, ApJ, 664, 384) • Up-scattered FS emission: Panaitescu (2008) • May help explain chromatic breaks

  27. GRB 090709 • BAT/XRT lightcurve

  28. GRB 090709 • XRT lightcurve

  29. GRB 090709 • BAT power spectrum • confirmed by K-W and INTEGRAL SPI-APS, Suzaku WAM Markwardt et al. 2009, GCNC 9645 P = 8.06 s Q ~ 11 p ~ 10-6

  30. GRB 090709 • Very bright burst: F~ 2.6e-5 ergs/cm2(Sakamoto et al., GCNC 9640) • Afterglow detected in H, K, not in J => z > 8.5 ??? (Aoki et al., GCNC 9634; Morgan et al., GCNC 9635) • But, reports of very early marginal detections in r’ suggest low redshift (Cenko et al., GCNC 9646) • NH measured by XRT suggests low redshift (Butler et al., GCNC 9639; Rowlinson et al., GCNC 9642) • No galaxy found in deep optical obs (i’ > 25.2, 10.4m GTC) (Castro-Tirado et al., GCNC 9655) • Nondetection of host galaxy, 8 s QPO, high b (200) and high NH suggest Galactic magnetar • No radio detection by WSRT or VLA

  31. The Future of Swift • Selected as #1 mission in the 2008 NASA Senior Review: • In the next 3-4 years we will obtain • more high redshift GRBs • GRB 090423: z=8.2 • more GRBs with good optical observations, • more short GRBs, and • more unusual cases (like 061007, 060614, 070110, …) • GRB 090709: QPO ??? • Fermi / Swift synergy • GBM: will provide MeV-range spectral data for many Swift GRBs • LAT: will discover very high energy (GeV) GRBs that can be localized by Swift • Enhanced LIGO (2009) • Will double detection range, may permit detection of inspiral sirens • Long-term: Advanced LIGO (c. 2013) • Simultaneous detection of short GRB by Swift and LIGO would provide “smoking gun” for merger picture • NS-NS inspiral out to 300 Mpc – up to 3/d • NS-BH inspiral to 650 Mpc

  32. Short GRBs • Major discovery of Swift is the first localizations of short GRBs, and the discovery that they occur in different environments than long GRBs • Consistent with origin from different progenitors (merging compact objects rather than collapsar)

  33. GRB 050509B 100x-1000x fainter than typical AG BAT: t-1.3 XRT: t-1.1 Chandra t90 = 0.04 s, Fluence = 2E-8 ergs/cm2 XRT counterpart in first 400 s, fades rapidly. 11 photons total. Location in cluster at z=0.226, near early-type galaxy. Possible NS-NS merger? XRT error circle on VLT image. XRT position is 9.8” from a bright elliptical galaxy at z=0.226

  34. Optical transient identified on edge of object D, an early-type galaxy at z=0.257, L=1.7L*, SFR < 0.02 Mo/yr. Another old, nearby elliptical galaxy associated with a short GRB!! Wiersema et al. 2005, GCN 3699 GRB 050724 WHT t90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB 050509B. (6E-7 ergs/cm2)

  35. Late-time bump (~1/2 day) t-0.8 GRB 050724 Possible evidence for NS-BH merger? t90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB 050509B. (6E-7 ergs/cm2) Slewed in 75 s. Very odd X-ray lightcurve. No evidence of jet break, θj > 0.5 rad for reasonable jet parameters Grupe et al. 2006

  36. Long-Term Future • Beyond Swift: the high z universe • Swift may be detecting high z bursts, but ground-based observations are required to identify them • SVOM • JANUS: identify high z GRBs and QSOs • Reionization • Star formation at high z • Xenia: High resolution spectroscopy of GRBs • Reionization • First stars • Cosmic Structure • WHIM

  37. Summary • Swift has compiled a large database of bursts and their X-ray and optical afterglows, discovering • Complex X-ray afterglows • X-ray flares, implying long-lived central engine activity • Prompt, accurate localization of short GRBs -> mergers • Bright, high-z bursts • Swift has increasingly become the satellite of choice for multiwavelength, rapid-response Targets of Opportunity • CVs and novae • SNe • Galactic transients • AGN and blazars • http://www.swift.psu.edu/too.html • Future prospects: • Swift/Fermi synergy • Swift/LIGO synergy -> compact mergers • JANUS, SVOM, and other proposed missions will focus on high-z

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