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

2  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? Talk Outline

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

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

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

GRB Keck GRB BeppoSAX Beppo-SAX & HETE-2 Era Fireball Model (Meszaros & Rees 1997)  -rays afterglow

7 The Time Gap Swift Beppo SAX data

GRB Progenitors Hypernova Merging Neutron Stars

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

10 Swift launch: 20 Nov 2004 !!

11 MOC Facility Has continuously operated Swift successfully from L+80 minutes to now! 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

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

13 BAT GRB Position Accuracy GRB b GRB GRB GRB GRB aGRB a BAT FSW (3’ radius) XRT Mean BAT position error: 52 arcseconds T. Sakamoto

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

15 Average Redshift - Pre-Swift: z = Swift: z = 2.3 Redshift and Time Distributions Redshift (z) Number of GRBs 5 10 Pre-Swift Swift Long GRBs Lookback Time (G yr) Era of GRBs Analysis by Neil Gehrels

16 72 Swift Long GRB Redshifts B A B B B A A A C A A B B A B A A = Redshift Swift Redshift Distribution Number Gehrels et al. 2007

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

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

19 III Cosmic Ray & Astrophysics School – Arequipa, Peru – 1 Sep 2008 Comparing Short and Long GRBs & GRB GRB = brightest long GRB GRB = brightest short GRB Norris et al. 2006

20 III Cosmic Ray & Astrophysics School – Arequipa, Peru – 1 Sep 2008 Comparing Short and Long GRBs & GRB GRB = brightest long GRB GRB = brightest short GRB Short GRB A Kouveliotou et al. 1993

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

22 Short GRBs - Opportunity Progress on short GRBs - a tough nut to crack! Swift statistics: 24 total short GRB (+ 3 questionable) * ~4 firm redshifts * 8 OTs * ~4 host galaxy IDs 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 , 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

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

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

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

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

GRB050416A > 58 Days α = 0.81 GRB is also still going with no jet break after 2 months!

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

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

30 Giant X-ray Flare: GRB B 500x increase! GRB Fluence: 8E-7 ergs/cm 2 Flare Fluence: 9E-7 ergs/cm 2 Burrows et al. 2005, Science; Falcone et al. 2005, ApJ Peak ~ 700 s Note establishment of AG before flare begins.

31 Swift XRT X-ray Flares GRB GRB GRB B GRB GRB GRB A GRB B GRB GRB GRB prompt afterglow detections ~ 50% have X-ray flares Typically in first 20 min. Dynamic range: 1.3x – 500x 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 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% Bromm & Loeb (2006) Swift GRB Rate z GRB Optical Brightness J = 3 hrs I = 2 min K = 23 hrs R = 1.5 hrs

35 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 Fraction with OT Fraction with z 239 Swift GRBs with XRT

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

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 underluminous underluminous normal GRB XRF underluminous no SN 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 N H 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

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

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

42 GSFC Swift Institutions 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