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

2. Fireball model: synchrotron emission from power-law distribution of electrons in highly relativistic outflows GRB afterglows E ~ 10 53 ergs T = 0 s R = 10 6 cm Pre- Burst Burst Afterglow Shock Formation Γ ~ 10 3 T ~ 10 2 s R = 3 x 10 12 cm T ~ 3 x 10 3 s R = 10 14 cm R = 3 x 10 16 cm T ~ 10 6 s γ, X X, optical, radio LOCAL MEDIUM

3. GRBs and Swift 20 November 2004

4. Burst Alert Telescope (BAT) 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) X-Ray Telescope (XRT) –0.2-10 keV –Few arcsecond positions –CCD spectroscopy UV/Optical Telescope (UVOT) UV/Optical Telescope (UVOT) –170 – 650 nm –Sub-arcsec positions –Grism spectroscopy –6 UV/optical broad-band filters –22 nd mag sensitivity (filtered) Spacecraft Spacecraft –Autonomous re-pointing, 20 - 75 sec –Onboard and ground triggers BAT XRT Spacecraft UVOT BAT UVOT XRT Swift Instruments All Swift data are immediately public http://swift.gsfc.nasa.gov/sdc/

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

6. Swift X-ray Afterglows > 370 Prompt X-ray LCs GRB 060204BGRB 060211AGRB 060306 GRB 060413GRB 060428AGRB 060502A GRB 060510A GRB 060510BGRB 060729 1e21e6

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

8. Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares 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 GRB 050730 Chincarini et al. 2007

9. 1 year! t j ~ 400 d θ j ~ 67° !! E γ ~ 3 x 10 51 erg GRB 060729 at z=0.54 (Grupe et al. 2008) Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares Jet breaks (or not…) Jet breaks (or not…) Torus Jet Relativistic beaming: θ ~ Γ -1 θjθj

10. GRB 060218 (Campana et al. 2006) Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares Jet breaks (or not…) Jet breaks (or not…) –First shock breakout from stellar surface: GRB 060218 / SN2006aj

11. GRB 071227 (D’Avanzo et al. 2007) VLT Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares Jet breaks (or not…) 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 Arcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitors New data hints at subclasses in redshift, offset, and progenitors

12. Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares Jet breaks (or not…) 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 Arcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitors New data hints at subclasses in redshift, offset, and progenitors –Nearby long GRBs with and without SNe Possible new classes of GRBs Possible new classes of GRBs GRB 060614 at z=0.125 (Gal-Yam et al. 2006)

13. Key Swift Discoveries GRBs GRBs –80% of world X-ray afterglows Complex X-ray lightcurves and flares Complex X-ray lightcurves and flares Jet breaks (or not…) 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 Arcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitors New data hints at subclasses in redshift, offset, and progenitors –Nearby long GRBs with and without SNe Possible new classes of GRBs 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 Includes transitions never before seen GRB 050730 at z=3.97 (Chen et al. 2005) z=6.7

14. 0 1 2 3 4 Vaughan et al. 2005 t -0.4 t -0.7 -0.73  0.11 t -5.2 -1.9  0.9 Zhang et al. 2006, ApJ, 642, 354 t -(2+β) ~ t -3 (Kumar & Panaitescu 2000) Emergence of afterglow Canonical LC: GRB 050315

15. X-ray Flares 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 GRB 050730

16. X-ray Flares 3x

17. X-ray Flares

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

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

20. Flare rise and fall times Mechanisms: 1)Ambient density fluctuations 2)Patchy shell 3)Refreshed shocks 4)Restarted central engine Ioka et al. 2005; Chincarini et al. 2007 Kinematically allowed regions for afterglow variability on-axis off-axis 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.

21. X-ray Flare Mechanism External Shocks? Rapid increase and decrease (Δt/t << 1) Rapid increase and decrease (Δt/t << 1) –Inconsistent with external shock Liang et al. (2006, ApJ, 646, 351) Liang et al. (2006, ApJ, 646, 351) Chincarini et al. (2007, ApJ, astro-ph/0702371) Chincarini et al. (2007, ApJ, astro-ph/0702371) Lazzati and Pernas (2007, MNRAS, 375, L46) Lazzati and Pernas (2007, MNRAS, 375, L46) Nakar & Granot (2007, MNRAS,380, 1744) Nakar & Granot (2007, MNRAS,380, 1744) Kocevski, Butler, & Bloom (2007, ApJ, 667, 1024) Kocevski, Butler, & Bloom (2007, ApJ, 667, 1024) Same underlying afterglow before and after Same underlying afterglow before and after –External shock already active before flare –Willingale et al. show that external shock present at end of prompt emission Enormous increase in several GRBs Enormous increase in several GRBs –GRB 050502B (500x), GRB 050916 (100x), GRB 050820 (100x) –Inconsistent with Inverse Compton mechanism –Inconsistent with reverse shock Simultaneous XRT/BAT pulses – clearly internal shocks (GRB 050820, GRB 060124, 061121, …) Simultaneous XRT/BAT pulses – clearly internal shocks (GRB 050820, GRB 060124, 061121, …)

22. X-ray Flare Mechanism External Shocks? Multiple flares in many bursts (e.g. GRB 050730) Multiple flares in many bursts (e.g. GRB 050730) –Inconsistent with one-shot models (e.g., afterglow onset) –No clear dividing line between γ -ray pulses and X-ray flares Krimm et al. (2007, ApJ, 665, 554) Krimm et al. (2007, ApJ, 665, 554) Flares in apparently “naked” GRBs (e.g. GRB 050421) Flares in apparently “naked” GRBs (e.g. GRB 050421) –Inconsistent with external shock, since no afterglow is seen General Consensus: flares are not generated in external shocks However: Dermer 2008 (ApJ, 684, 430) argues that thin clouds interacting with the external shock can produce X-ray flares for R>10 17 cm, Δx~10 15 cm, n~10 3 cm

23. Flare Mechanisms (D. Morris, PhD thesis, 2008) Compare each flare to required characteristics of several models 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 Implies IS most likely model for any particular flare, but likely need several models to explain the entire collection of GRB X- ray flares

24. X-ray Flare Mechanism Internal Shocks? All of previous points are consistent with internal shocks. All of previous points are consistent with internal shocks. Spectral evolution of flares consistent with spectral evolution of prompt pulses Spectral evolution of flares consistent with spectral evolution of prompt pulses Burrows et al. (2005, Science, 309, 1833) Burrows et al. (2005, Science, 309, 1833) Falcone et al. (2005, ApJ, 641, 1010) Falcone et al. (2005, ApJ, 641, 1010) Pagani et al. (2006, ApJ, 645, 1613) Pagani et al. (2006, ApJ, 645, 1613) Burrows et al. (2007, Phil. Trans. Royal Soc. A., 365, 1213) Burrows et al. (2007, Phil. Trans. Royal Soc. A., 365, 1213) Butler & Kocevski (2007, ApJ, 668, 400) Butler & Kocevski (2007, ApJ, 668, 400) Examination of post-flare decay slopes suggests that “clock” is reset at beginning of each flare Examination of post-flare decay slopes suggests that “clock” is reset at beginning of each flare Liang et al. (2006, ApJ, 646, 351) Liang et al. (2006, ApJ, 646, 351) Requires late-time activity of central engine => central engine restarts as late at 10 4 s after burst. Requires late-time activity of central engine => central engine restarts as late at 10 4 s after burst. Upscattered emission? Panaitescu (2008, MNRAS, 383, 1143) Panaitescu (2008, MNRAS, 383, 1143)

25. Plateau Phase GRB 060729 Plateau phase ~ 40 ks

26. Swift X-ray Afterglows GRB 060204B GRB 060211AGRB 060306 GRB 060413GRB 060428AGRB 060502A GRB 060510AGRB 060510BGRB 060729

27. Plateau Phase Thought to be energy injection into the external shock, either by Thought to be energy injection into the external shock, either by 1.Delayed impacts of slower shocks created at the time of the burst, or 2.Late-time ejection of relativistic shells from the central engine Difficult to distinguish between these alternatives in most cases. Difficult to distinguish between these alternatives in most cases.

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

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

30. Plateau Phase Other recent examples:

31. Plateau Phase Other recent examples:

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

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

34. GRB 090709 BAT/XRT lightcurve BAT/XRT lightcurve

35. GRB 090709 XRT lightcurve XRT lightcurve

36. GRB 090709 BAT power spectrum 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

37. GRB 090709 Very bright burst: F~ 2.6e-5 ergs/cm 2 (Sakamoto et al., GCNC 9640) Very bright burst: F~ 2.6e-5 ergs/cm 2 (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) 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) –N H 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) 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 (20 0 ) and high N H suggest Galactic magnetar No radio detection by WSRT or VLA No radio detection by WSRT or VLA

38. The Future of Swift Selected as #1 mission in the 2008 NASA Senior Review: 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 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 ??? GRB 090709: QPO ??? Fermi / Swift synergy 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) Enhanced LIGO (2009) –Will double detection range, may permit detection of inspiral sirens Long-term: Advanced LIGO (c. 2013) 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

39. 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 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) Consistent with origin from different progenitors (merging compact objects rather than collapsar)

40. GRB 050509B t 90 = 0.04 s, Fluence = 2E-8 ergs/cm 2 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? BAT: t -1.3 XRT: t -1.1 XRT error circle on VLT image. XRT position is 9.8” from a bright elliptical galaxy at z=0.226 Chandra 100x-1000x fainter than typical AG

41. GRB 050724 t 90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB 050509B. (6E-7 ergs/cm 2 ) WHT Wiersema et al. 2005, GCN 3699 Optical transient identified on edge of object D, an early-type galaxy at z=0.257, L=1.7L*, SFR < 0.02 M o /yr. Another old, nearby elliptical galaxy associated with a short GRB!!

42. GRB 050724 t 90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB 050509B. (6E-7 ergs/cm 2 ) Slewed in 75 s. Very odd X-ray lightcurve. No evidence of jet break, θ j > 0.5 rad for reasonable jet parameters t -0.8 Possible evidence for NS-BH merger? Late-time bump (~1/2 day) Grupe et al. 2006

43. Long-Term Future Beyond Swift: the high z universe 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 Reionization Star formation at high z Star formation at high z –Xenia: High resolution spectroscopy of GRBs Reionization Reionization First stars First stars Cosmic Structure Cosmic Structure WHIM WHIM

44. Summary Swift has compiled a large database of bursts and their X-ray and optical afterglows, discovering 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 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: Future prospects: –Swift/Fermi synergy –Swift/LIGO synergy -> compact mergers –JANUS, SVOM, and other proposed missions will focus on high-z