Swift Observations of GRBs David Burrows The Pennsylvania State University

2008 Nanjing GRB Conference GRBs and Swift 20 November 2004

2008 Nanjing GRB Conference Burst Alert Telescope (BAT) Burst Alert Telescope (BAT) – 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) – 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, sec –Onboard and ground triggers BAT XRT Spacecraft UVOT BAT UVOT XRT Swift Instruments

2008 Nanjing GRB Conference Swift GRBs (> 330 so far) Short GRB FRED Fast Rise Exponential Decay 88% followed up with XRT/UVOT observations

2008 Nanjing GRB Conference Beppo-SAX afterglows: de Pasquale et al. 2006, AA, 455, 813 GRB GRB GRB GRB GRB GRB GRB GRB GRB e41e6

2008 Nanjing GRB Conference Swift X-ray Afterglows ~ 225 Prompt X-ray LCs GRB BGRB AGRB GRB GRB AGRB A GRB A GRB BGRB e21e6

2008 Nanjing GRB Conference Afterglow Statistics LGRBs: Detected 253/262 = 97% with XRT T < 200 ks) Compare with 55 LGRB afterglows before Swift launch Handful of long GRBs not detected by XRT SGRBs: Detected ~23/31 = 74% with XRT T < 200 ks) Compare with 0 SGRB afterglows before Swift launch XRT: All Swift GRBs: Detected 276/293 = 94% with XRT T < 200 ks) > 80% of the X-ray afterglows ever detected! ~90% have prompt slews (< 300 s, excluding Aug-Oct 2007) Optical: UVOT: ~ 40% detection rate Total optical: ~ 60% detection rate, ~ 33% with redshifts

2008 Nanjing GRB Conference Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts (>70% of world total) –80% of world X-ray afterglows Complex X-ray lightcurves and flares – see O’Brien and Chincarini talks this PM Complex X-ray lightcurves and flares – see O’Brien and Chincarini talks this PM

2008 Nanjing GRB Conference 1 year! t j ~ 400 d θ j ~ 67° !! E γ ~ 3 x erg GRB at z=0.54 (Grupe et al. 2008) Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…)

2008 Nanjing GRB Conference Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…) –“Naked-eye GRB”: GRB B (see session on Tuesday PM) GRB B (Racusin et al. 2008)

2008 Nanjing GRB Conference GRB (Campana et al. 2006) Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…) –“Naked-eye GRB”: GRB B –First shock breakout from stellar surface: GRB / SN2006aj

2008 Nanjing GRB Conference GRB (D’Avanzo et al. 2007) VLT Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…) –“Naked-eye GRB”: GRB B –First shock breakout from stellar surface: GRB / 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

2008 Nanjing GRB Conference GRB at z=0.125 (Gal-Yam et al. 2006) Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…) –“Naked-eye GRB”: GRB B –First shock breakout from stellar surface: GRB / 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

2008 Nanjing GRB Conference Key Swift Discoveries GRBs GRBs –> 240 GRBs with arcsec positions –~ 100 GRBs with redshifts –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…) –“Naked-eye GRB”: GRB B –First shock breakout from stellar surface: GRB / 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=6.3) using GRBs Includes transitions never before seen Includes transitions never before seen GRB at z=3.97 (Chen et al. 2005)

2008 Nanjing GRB Conference 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)

2008 Nanjing GRB Conference GRB Classification Bimodal distribution of durations - Short, hard GRBs: mergers - Long, soft GRBs: collapsars Short Bursts: mergers Old (few billion yrs) Outside galaxies Long Bursts: collapsars Young (few million yrs) Star-forming regions

2008 Nanjing GRB Conference GRB Classification Horvath et al. 2002, AA, 392, 791 Short/hard Long/soft Donaghy et al. 2006, astro-ph/ E. Nakar, 2006

2008 Nanjing GRB Conference ~35 Short GRBs (33 from Swift BAT)

2008 Nanjing GRB Conference GRB B 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 Gehrels et al. 2005, Nature

2008 Nanjing GRB Conference GRB050709: Second Short GRB Afterglow Discovered by the HETE-II satellite X-ray counterpart found by Chandra X-ray Observatory Optical counterpart found by ground-based telescopes Located at edge of star-forming galaxy at z=0.16 Danish 1.54m La Silla telescope (Jensen et al. 2005, GCN 3589; Price et al. 2005, GCN 3612) Fox et al. 2005

2008 Nanjing GRB Conference GRB WHT Wiersema et al. 2005, GCN 3699 Optical transient located on edge of 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!! t 90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB B.

2008 Nanjing GRB Conference GRB No evidence of jet break, θ j > 0.5 rad for reasonable jet parameters t -0.8 Late-time bump (~1/2 day) Grupe et al. 2006

2008 Nanjing GRB Conference ~30 photons t GRB

2008 Nanjing GRB Conference Possible association with elliptical galaxies in cluster at z~ (or 1.8 – Berger) GRB

2008 Nanjing GRB Conference Swift Short GRBs without afterglows GRB : t 90 = 0.13 s XRT observations began at T+79 s No X-ray counterpart – very unusual GRB (short, soft) t 90 = 0.07 s XRT observations began at T+92 s No X-ray counterpart – very unusual GRB A t 90 = 0.03 s XRT observations began at T+68 s No X-ray counterpart – very unusual GRB t 90 = 2.2 s XRT observations began at T+126 ks No X-ray counterpart

2008 Nanjing GRB Conference GRB t flare No clear optical counterpart or redshift, but near z=0.114 cluster Mangano et al Naked GRB

2008 Nanjing GRB Conference Soderberg et al. 2006GRB051221A

2008 Nanjing GRB Conference z= E p = 402 keV E iso = 2.4E51 Clear jet break implies θ j ~ 4-8˚ Similar to long bursts GRB A t Burrows et al t t GRB051221A

2008 Nanjing GRB ConferenceGRB z=0.714 ?? E p = 100 keV t -1.13

2008 Nanjing GRB Conference Many small flares Energy injection t GRB

2008 Nanjing GRB Conference Many small flares in early X-ray light curve. Interpret as variable circum-burst medium, with cooling frequency dropping through X-ray band during orbital gap. Small flares in later optical light curve. Roming et al., ApJ, 651, 985 GRB

2008 Nanjing GRB Conference Short GRBs (through 2006) GRBTail? t 90 (s) t followup Afterglow Redshift - 1 GRB B s X0.225 Possible host galaxy / cluster 2 GRB Y ks X, O Optical afterglow 3 GRB Y s X, O, R Optical afterglow 4 GRB s X 0.7? / 1.8? Possible host galaxies 5 GRB s Marginal X ? 6 GRB s None? 7 GRB A s None? 8 GRB ks None? 9 GRB s X0.114? Possible host galaxy 10 GRB A 4.8 > 11.2 ks None? 11 GRB A s X, O, R Optical afterglow 12 GRB Y8 93 s X, O Optical afterglow 13 GRB Y ks X, O 4.6?? Possible host galaxy 14 GRB s X, O ? 15 GRB B s X? 16? GRB ks X, O 0.089? Possible host, SF region? 17? GRB Y s X, O Optical afterglow, no SN 18 GRB s X1.131?? Possible host galaxy 19 GRB Y s X, O ? 20 GRB s X, O / Possible host galaxy/cluster 21 GRB Y ks X0.41? Possible host galaxy 22 GRB s X0.827? Possible host galaxy

2008 Nanjing GRB Conference Gorosabel et al. 2006, AA, astro-ph/ Short GRB hosts

2008 Nanjing GRB Conference Long vs short GRB energetics Long GRBs, from Panaitescu 2005) short GRBs long GRBs T 90 / (1+z) (s) E iso (erg) Swift GRBs

2008 Nanjing GRB Conference Fundamental questions on short GRBs What can we hope to learn about short GRBs from X-ray afterglows? What are the progenitors of short GRBs? Are there subclasses of short GRBs? How do short GRB afterglows differ from long GRB afterglows? What can we learn about short GRB environments? What can we learn about the central engines of short GRBs?

2008 Nanjing GRB Conference Short GRB Environments: “normal” decays t t t B t (HETE-2) B t ~ 25% of sample No evidence for decay of prompt emission => consistent with short duration of bursts -exception: , which had a soft tail to the prompt emission Simple afterglows without energy injection phase Afterglows commence by beginning of XRT observations (~ 100 s after burst) BAT XRT

2008 Nanjing GRB Conference Short GRB Environments: “canonical afterglows” t -2.3 t t -1.5 t -0.5 t -2.2 t -0.1 t -0.7 t -1.8 t t t -0.8 t t A t ~ 25% of sample Evidence for decay of prompt emission in 3 bursts: , , All three of these have soft tails in the BAT data All have evidence for energy injection phases Afterglows commence by beginning of XRT observations (~ 100 s after burst)

2008 Nanjing GRB Conference Short GRB Environments: “Naked” GRBs t t t t t -2.3 Combining with the 9 non-detections of short GRBs with prompt slews, we have >13/33 possible “naked” short GRBs, vs 5/210 possible “naked” long GRBs. => Consistent with lower density environments for short GRBs. Short GRBs without X-ray afterglows: , , A, , , B, , B,

2008 Nanjing GRB Conference Short GRB Central Engines: Flares t -0.8 t t t t t -1.2 X-ray flares seen in ~50% of long GRBs Evidence for flaring in ~20% of short GRBs => short GRBs need to keep central engine running for hundreds of seconds

2008 Nanjing GRB Conference Short GRB Central Engines: Energy Injection t -0.8 t t t t A t t -1.5 t -2.2 t -0.1 t t -0.7 t -1.8 t t -0.5 t Two flavors: Continuous energy injection: shallow decays Episodic energy injection: injection period followed by return to original decay slope

2008 Nanjing GRB Conference Short GRB Summary X-ray afterglows similar to long GRBs, but fainter and less complex X-ray afterglows similar to long GRBs, but fainter and less complex Late central engine activity implied by flares and energy injection in X-ray afterglows Late central engine activity implied by flares and energy injection in X-ray afterglows High incidence of naked GRBs => low density environments High incidence of naked GRBs => low density environments “Missing” hosts “Missing” hosts –Ejections from hosts? –High redshift? Possible subclasses: Possible subclasses: –Extended soft tails –Late central engine activity

2008 Nanjing GRB Conference GRB Classification Horvath et al. 2002, AA, 392, 791 Donaghy et al Short/hard Long/soft E. Nakar, 2006 Gehrels et al The problem with GRBs is that we have no clear-cut emperical classification scheme: –Considerable overlap in durations and spectral properties between the “long” and “short” populations –Increasing sample of “short/hard” GRBs with long soft tails (~ 33%) , , , , , , B, , , , , , , , B, , These often have t90 >> 5s as measured by Swift/BAT These often have t90 >> 5s as measured by Swift/BAT

2008 Nanjing GRB Conference Long Soft Tails of Short GRBs Norris & Bonnell 2006, ApJ, 643, 266 Villasenor et al. 2005, Nature, 437, 855 GRB

2008 Nanjing GRB Conference Long Soft Tails of Short GRBs Barthelmy et al. 2005, Nature, 438, 994 GRB GRB

2008 Nanjing GRB ConferenceGRB Weak burst that did not trigger BAT Ground processing revealed weak source Late notification and slew t 90 = 4 s Optical transient in SF region of spiral galaxy (Sc-type) No associated SN to very low limits Either short GRB (Ofek et al.) or long GRB (Fynbo et al.) Ofek et al.

2008 Nanjing GRB Conference GRB Duration: t 90 = 102s => “long”/Type II Duration: t 90 = 102s => “long”/Type II Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter, harder, and more variable in this case) Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter, harder, and more variable in this case)

2008 Nanjing GRB Conference Mangano et al., A&A, 470, 105 GRB060614

2008 Nanjing GRB Conference Optical: Break at 30 ks slope of 1.1 Second break at 104 ks slope of 2.4 Break at 100 ks seen in both X-ray and optical => achromatic break to slope of about 2.4  Jet break.  θ j = 10.5° (n/3) 1/8 (η/0.2) 1/8  E γ = 4 x ergs Mangano et al., A&A, 470, 105 GRB060614

2008 Nanjing GRB Conference BAT+XRT Spectral Fit Fit to Band model gives E p = 8 keV in this time interval. E p ~ 10 keV early, then drops through the X-ray band. Mangano et al., A&A, 470, 105 GRB060614

2008 Nanjing GRB Conference Mangano et al., A&A, 470, 105 UVOT+XRT SED Early: UVOT and XRT inconsistent  Different spectral segments  Cooling frequency must fall near the UV After 30 ks, XRT and UVOT consistent with a single synchrotron spectrum. GRB060614

2008 Nanjing GRB ConferenceGRB Gal-Yam et al., Nature

2008 Nanjing GRB Conference Gehrels et al. 2006, Nature GRB060614

2008 Nanjing GRB Conference Zhang et al. 2007, ApJ, submitted GRB060614

2008 Nanjing GRB Conference The enigmatic case of GRB The problem with GRBs is that we have no clear-cut emperical classification scheme: –Considerable overlap in durations and spectral properties between the “long” and “short” populations –Increasing sample of “short/hard” GRBs with long soft tails , , , , , , , , , , These often have t 90 >> 5s as measured by Swift/BAT These often have t 90 >> 5s as measured by Swift/BAT –Case of GRB (Donaghy et al.) => argument for multidimensional classification, new terminology (“short/long population GRBs”) –Case of GRB => suggestion for Type I/Type II classification (Zhang et al 2007, ApJ; Zhang 2006, Nature) Duration: t 90 = 102s => “long”/Type II Duration: t 90 = 102s => “long”/Type II Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter and more variable in this case) Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter and more variable in this case) Location: outskirts of host galaxy => “short”/Type I Location: outskirts of host galaxy => “short”/Type I Lack of SN => short/Type I or unusual “long”/Type II Lack of SN => short/Type I or unusual “long”/Type II Lag-luminosity relation: small lag => “short”/Type I Lag-luminosity relation: small lag => “short”/Type I E iso ~ ergs, E γ ~ 4 x ergs E iso ~ ergs, E γ ~ 4 x ergs => intermediate between Type I and Type II

2008 Nanjing GRB Conference XRT Afterglow Statistics Mean redshift for long GRBs is ~2.4 Mean redshift for short GRBs is ~0.5 8 GRBs with z > 4.0 (none since )

2008 Nanjing GRB Conference Keck Spectroscopy of GRB Berger et al Metallicity vs Redshift z = Damped Ly  - N(HI)=10 22 cm -2 - n ~ 10 2 cm -3 - Z = 0.06 Z O - M progenitor < 25 M O..

2008 Nanjing GRB Conference Subaru spectrum of GRB : z = ± Kawai et al N H =4E21

2008 Nanjing GRB Conference Summary The XRT is performing well. Current efforts are focussing on analysis of database of > 200 afterglows. XRT is increasingly being used for ToOs and other non-GRB science programs.

2008 Nanjing GRB Conference 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 –more GRBs with good optical observations, –more short GRBs, and –more unusual cases (like , , , …) Starting subthreshold trigger experiment to search for weak bursts in the noise Starting subthreshold trigger experiment to search for weak bursts in the noise GLAST / Swift synergy GLAST / 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 (~ 1 / month) Investigating possibility of rapid Swift responses to LAT GRBs Investigating possibility of rapid Swift responses to LAT GRBs 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

2008 Nanjing GRB Conference 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

2008 Nanjing GRB Conference JANUS SMEX mission selected for Phase A studies (launch in mid-2012) SMEX mission selected for Phase A studies (launch in mid-2012) X-ray Flash Monitor ( keV) + NIR Telescope ( μ m, R=14) X-ray Flash Monitor ( keV) + NIR Telescope ( μ m, R=14) –Optimized for detection and identification of high-z GRBs –> 50 GRBs with 5 50 GRBs with 5 < z < 12 Star formation rate, finder for ground-based followup Star formation rate, finder for ground-based followup –20,000 sq degree spectroscopic sky survey to discover > < z < 10

2008 Nanjing GRB Conference Xenia Instrumentation Instrumentation –Wide Field Monitor (similar to Swift BAT) –Wide Field Imager (similar to Swift XRT, but > 1° x 1°) –Wide Field Spectrometer (microcalorimeter, 0.7° x 0.7°) –GRB Monitor (MeV range)

2008 Nanjing GRB Conference Xenia Xenia

2008 Nanjing GRB Conference 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 Future prospects: Future prospects: –Swift/GLAST synergy –Swift/LIGO synergy -> compact mergers –JANUS, SVOM, and other proposed missions will focus on high-z