John Nousek (Penn State University)

1. ly Searching the Sky: The First Three Years of the Swift Gamma-Ray Burst Explorer John Nousek (Penn State University) III Cosmic Ray & Astrophysics School - Arequipa, Peru – 1 Sep 2008

2. Talk Outline • GRBs – Pre-Swift • GRB Phenomenon • Pre-Swift GRB Paradigm • Swift Era • Swift satellite • Swift discoveries • Challenges to the GRB Paradigm • Short GRBs • ‘Canonical’ X-ray light curves • Lack of jet breaks/chromatic jet breaks • X-ray ‘flares’ • Swift & GRB science in the future • What to do with Swift for the next four years?

3. GRBs – Pre-Swift What did we know about GRBs before Swift?

4. History of GRBs • GRBs discovered in 1969 by Ray Klebesadel of LANL • Vela satellites: monitored Nuclear Test Ban treaty • Data published in 1973 • Compton Gamma-Ray Observatory launched on 5 April 1991 • BATSE: 2609 bursts in 8.5 years

5. Hard Hardness Ratio short long Soft Duration (s) Compton Observatory Era

6. afterglow g-rays Fireball Model (Meszaros & Rees 1997) Beppo-SAX & HETE-2 Era GRB 970228 - BeppoSAX GRB 971214 - Keck

7. The Time Gap Swift Beppo SAX data

8. Hypernova Merging Neutron Stars GRB Progenitors

9. The Swift Era What have we learned so far from Swift?

10. Swift launch: 20 Nov 2004 !!

11. MOC Facility Located in State College, PA ~ 4 km. from Penn State campus Flight Operations Team (FOT) – responsible for observatory Health & Safety Science Operations Team (SOT) - responsible for scientific operation of Swift Has continuously operated Swift successfully from L+80 minutes to now!

12. BAT Burst Image XRT Image UVOT Image T<20 sec T<90 sec T<300 sec BAT Error Circle Observing Scenario 1. Burst Alert Telescope triggers on GRB, calculates position on sky to ~ 1 arcmin 2. Spacecraft autonomously slews to GRB position in 20-70 s 3. X-Ray Telescope determines position to ~2-3 arcseconds 4. UV/Optical Telescope images field, transmits finding chart to ground

13. BAT GRB Position Accuracy GRB 050215b GRB 050319 GRB 050315 XRT BAT FSW (3’ radius) GRB 050406 GRB 050416a GRB 050509a Mean BAT position error: 52 arcseconds T. Sakamoto

14. Short GRB FRED Fast Rise Exponential Decay Short GRB ~300 GRB discovered 85% with X-ray detections 95% with XRT @ T<200 ks ~60% with optical detection (UVOT + ground) ~9% short GRBs Swift Statistics: >400 non-GRB TOOs >100,000 slews

15. Era of GRBs Long GRBs 20 10 Swift 15 Pre-Swift Number of GRBs 10 5 5 0 0 0.1 1.0 10.0 1.0 10.0 Redshift (z) Lookback Time (G yr) Redshift and Time Distributions • Average Redshift • Pre-Swift: z = 1.2 • Swift: z = 2.3 Analysis by Neil Gehrels

16. Swift Redshift Distribution 0.001 0.01 0.1 1 10 Redshift 2.20 050922C 2.17 070810 2.15 071020 2.04 070611 1.95 050315 1.56 050801 1.55 051111 1.55 070125 1.51 060502A 1.50 070306 1.49 060418 1.44 050318 1.31 061121 1.29 050126 1.26 061007 1.17 070208 1.16 061126 0.98 071010 0.97 070419A 0.95 071010B 0.94 051016B 0.84 060814 0.84 070318 0.83 050824 0.78 060202 0.76 061110A 0.70 060904B 0.65 050416A 0.61 050525A 0.59 050223 0.54 060729 0.44 060512 0.30 050826 0.125 060614 0.089 060505 0.033 060218 6.29 050904 5.47 060927 5.3 050814 5.11 060522 4.9 060510B 4.41 060223A 4.27 050505 4.05 060206 3.97 050730 3.91 060210 3.71 060605 3.69 060906 3.63 070721B 3.53 060115 3.44 061110B 3.43 060707 3.36 061222B 3.34 050908 3.24 050319 3.22 060526 3.20 060926 3.08 060607A 2.95 070411 2.90 050401 2.82 050603 2.71 060714 2.69 071031 2.68 060604 2.61 050820A 2.50 070529 2.45 070802 2.43 060908 2.35 051109A 2.35 070110 2.31 070506 2.30 060124 72 Swift Long GRB Redshifts < z > = 2.3 Number Gehrels et al. 2007

17. GRBs – now in the Swift era How has the paradigm changed with the Swift discoveries?

18. Long Short XRT BAT Short vs Long GRBs Short GRB Long GRB Cnts/s Cnts/s Swift first to discover counterpart to short GRB! GRB 050509B - Swift VLT Image GRB 990123 - BeppoSAX HST Image Short GRBs in non-SF galaxies/regions Long GRBs in SF galaxies GRB

19. & GRB 061210 Comparing Short and Long GRBs Norris et al. 2006 GRB 061121 = brightest long GRB GRB 061210 = brightest short GRB

20. & GRB 061210 Comparing Short and Long GRBs Short GRB 051221A GRB 061121 = brightest long GRB GRB 061210 = brightest short GRB Kouveliotou et al. 1993

21. Long GRBs Short GRBs Prompt vs Afterglow Correlation Analysis Gehrels et al. 2007

22. Swift statistics: 24 total short GRB (+ 3 questionable) * ~4 firm redshifts * 8 OTs * ~4 host galaxy IDs Short GRBs - Opportunity Short bursts versus Long bursts - Different physics - Different environments - Different population of stars - Different ages & distances New tool for studying stellar evolution & binary formation Direct tie-in to emerging GW field CHALLENGE: Short GRBs are weak in g, X, opt Current knowledge from few events GRBs with afterglow - special subclass? Which are short, which are long? Needed:more short GRBs rapid, sensitive follow-up high resolution optical imaging Progress on short GRBs - a tough nut to crack!

23. Pre-Swift X-ray light curve Swift Beppo SAX data

24. Canonical Swift XRT Light Curve (steep – due to light delay effects from end of prompt emission) Flare (plateau – due to energy injection into external shock) (normal – external shock) Jet Break GRB060428A – Courtesy of D. Burrows

25. Jet Break Jet Relativistic beaming: θ ~ Γ-1 Torus Frail et al. 2001, ApJ, 562, L55

26. Jet Break Jet break knowledge is critical for GRB energetics: E γ = Eiso(1-cos θj) Frail et al. 2001, ApJ, 562, L55

27. GRB050416A GRB060729 is alsostill going with no jet break after 2 months! α = 0.81 > 58 Days

28. Jet Break For some Swift bursts there is either no jet break, or there is a chromatic break → Either jet angle is very wide or Density is very low or Basic model is wrong Jet Relativistic beaming: θ ~ Γ-1 Torus Frail et al. 2001, ApJ, 562, L55

29. Giant X-ray Flare: GRB 060526 > 100x increase! Peak ~ 220 s

30. Giant X-ray Flare: GRB 050502B 500x increase! • GRB Fluence: • 8E-7 ergs/cm2 • Flare Fluence: • 9E-7 ergs/cm2 Peak ~ 700 s Burrows et al. 2005, Science; Falcone et al. 2005, ApJ Note establishment of AG before flare begins.

31. GRB 050406 GRB 050421 GRB 050502B GRB 050607 GRB 050712 GRB 050713A GRB 050716 GRB 050714B Swift XRT X-ray Flares 116 prompt afterglow detections ~ 50% have X-ray flares Typically in first 20 min. Dynamic range: 1.3x – 500x GRB 050726 GRB 050730 Flare analysis courtesy of Dave Burrows

32. Flares in Short GRBs ? Mechanism for flares must also operate in the context of short GRBs.

33. The Future What to do with Swift for the next four years?

34. Swift GRB Rate Bromm & Loeb (2006) High-z GRB - Opportunity Prediction: - 7% - 10% of Swift GRBs at z>5 (Bromm & Loeb, Jakobbson et al., Lamb & Reichart) - ~0.5% at z>10 Swift measurements: - 4 out of 72 = 6% z GRB Optical Brightness 6.29 050904 J = 18 @ 3 hrs 5.6 060927 I = 16 @ 2 min 5.3 050814 K = 18 @ 23 hrs 5.11 060522 R = 21 @ 1.5 hrs GRBs are bright !

35. 239 Swift GRBs with XRT Fraction with OT Fraction with z 2007 2005 2006 High-z GRB - Opportunity GRBs are briefly the most luminous sources in the universe .... across the E-M spectrum! High-z GRBs offer unique tool for studying: - Reionization era - Abundance history of universe - First stars & first light - Star formation rate history - Gas and dust content of early galaxies CHALLENGE: Difficult to determine redshift for high-z bursts Bursts not detected in optical can be common dark GRBs or rare high-z events. Needed: rapid response, large telescope, IR spectrograph Needed: redshift indicators, good position on sky for follow-up

36. 3 GRB SNe SN 2006aj BAT SNe Ic GRB 060218: GRB + Supernova Super-long GRB - ~35 minutes BAT, XRT, UVOT during GRB z = 0.033 d = 145 Mpc SN 2006aj SN Ib/c Eiso = few x 1049 erg - underluminous Epeak = 4.9 keV - XRF Pian et al. 2006 Campana et al., Mazzali et al., Pian et al., Soderberg et al.

37. Underluminous GRBs - Opportunity Observations of nearby GRBs leading to breakthroughs in understanding of: - GRB central engine - Jet outflows - CC supernovae CHALLENGE: Data are scarce and puzzling: 6 events, all different - 980425 underluminous - 031203 underluminous - 030329 normal GRB - 060219 XRF underluminous - 060505 no SN - 060614 no SN Needed: better detection of faint GRBs

38. The Year of High-z Bursts Alerts from Swift data - BAT T90, variability, spectrum (Ukwatta & Sakamoto 2007) - X-ray light curve flaring (Morris et al. 2007) - X-ray NH correlations (Grupe et al. 2007) - UVOT photometric data (Vanden Berk 2007) Sun Angle - 50% of time with Swift pointing >9hr from sun Follow-up Community - Small & medium telescopes to identify candidates - Large telescope for spectra of likely candidates

39. 3 hr 9 hr All GRBs 2006 Number of GRBs 1.0 Fraction of GRBs with z April 2007 Sun angle [deg] Nov. 2007 Sun Angle Pointing angle relative to Sun Advantage of high sun angle Sakamoto 2007

40. BAT Low Threshold Experiment Lower BAT thresholds: ~2 triggers & slews per day Observe with NFIs for 2 ks Trigger is deemed a GRB if afterglow is detected No Notices or Circulars for triggers without afterglow Observers can sign up to receive all triggers, with suitable warnings Experiment to last 1 month Barthelmy, Palmer, Fenimore

41. H.E. g-Ray z=5 IR Afterglow z=15 Dermer, Chiang & Mitman (2000) JWST sensitivity Bromm & Loeb (2007) Opportunities for Joint Observations AGILE & GLAST H.E. g-rays JWST (2013) IR ALMA (2012) radio mm/submm ICECUBE (2009 -2011) neutrinos LIGO (2014 - ALIGO) gravitational wave ~30 NS-NS mergers per year

42. Swift Institutions GSFC Executive Committee G. Chincarini - Brera Obs. N. Gehrels - GSFC P. Giommi - ASI K. Mason - MSSL J. Nousek - PSU J. Osborne - U. Leicester A. Wells - U. Leicester N. White - GSFC