Swift Observations of GRBs

David BurrowsThe Pennsylvania State University

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GRBs and SwiftGRBs and Swift

20 November 2004

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Burst Alert Telescope (BAT)Burst Alert Telescope (BAT)– 15-150 keV15-150 keV– 2 sr field of view2 sr field of view– CdZnTe detectorsCdZnTe detectors– Most sensitive gamma-ray Most sensitive gamma-ray

imager ever imager ever– Detect ~100 GRBs per yearDetect ~100 GRBs per year

X-Ray Telescope (XRT)X-Ray Telescope (XRT)– 0.2-10 keV0.2-10 keV– Few arcsecond positionsFew arcsecond positions– CCD spectroscopyCCD spectroscopy

UV/Optical Telescope (UVOT)UV/Optical Telescope (UVOT)– 170 – 650 nm170 – 650 nm– Sub-arcsec positionsSub-arcsec positions– Grism spectroscopyGrism spectroscopy– 6 UV/optical broad-band filters6 UV/optical broad-band filters– 2222ndnd mag sensitivity (filtered) mag sensitivity (filtered)

SpacecraftSpacecraft– Autonomous re-pointing, 20 - 75 Autonomous re-pointing, 20 - 75

secsec– Onboard and ground triggersOnboard and ground triggers

BAT

XRT

Spacecraft

UVOT

BAT

UVOT

XRT

Swift InstrumentsSwift Instruments

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Swift GRBs (> 330 so far)Swift GRBs (> 330 so far)

Short GRB

Short GRB

FRED

Fast Rise Exponential Decay

88% followed up with XRT/UVOT observations

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Beppo-SAX afterglows: de Pasquale et al. 2006, AA, 455, 813

GRB 000529 GRB 000615

GRB 000926 GRB 001109

GRB 010214 GRB 010222

GRB 990806

GRB 991106

GRB 000214

2e4 1e6

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Swift X-ray AfterglowsSwift X-ray Afterglows~ 225 Prompt X-ray LCs

GRB 060204B GRB 060211A GRB 060306

GRB 060413 GRB 060428A GRB 060502A

GRB 060510A GRB 060510B GRB 060729

1e2 1e6

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Afterglow StatisticsAfterglow Statistics

• LGRBs:• Detected 253/262 = 97% with XRT (observed @ 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 (observed @ T < 200 ks)

• Compare with 0 SGRB afterglows before Swift launch

XRT:• All Swift GRBs:

• Detected 276/293 = 94% with XRT (observed @ 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

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Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts (>70% of world total)~ 100 GRBs with redshifts (>70% of world total)– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flares – see O’Brien and Chincarini talks Complex X-ray lightcurves and flares – see O’Brien and Chincarini talks this PMthis PM

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1 year!

tj ~ 400 d

θj ~ 67° !!

Eγ ~ 3 x 1051 erg

GRB 060729 at z=0.54(Grupe et al. 2008)

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

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Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

– ““Naked-eye GRB”: GRB 080319BNaked-eye GRB”: GRB 080319B

(see session on Tuesday PM)(see session on Tuesday PM) GRB 080319B(Racusin et al. 2008)

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GRB 060218(Campana et al. 2006)

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

– ““Naked-eye GRB”: GRB 080319BNaked-eye GRB”: GRB 080319B– First shock breakout from stellarFirst shock breakout from stellar

surface: GRB 060218 / SN2006ajsurface: GRB 060218 / SN2006aj

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GRB 071227(D’Avanzo et al. 2007)

VLT

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

– ““Naked-eye GRB”: GRB 080319BNaked-eye GRB”: GRB 080319B– First shock breakout from stellarFirst shock breakout from stellar

surface: GRB 060218 / SN2006ajsurface: GRB 060218 / SN2006aj– Short GRBs with large and small redshiftsShort GRBs with large and small redshifts

Arcsecond localizations => evidence for compact mergersArcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitorsNew data hints at subclasses in redshift, offset, and progenitors

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GRB 060614 at z=0.125(Gal-Yam et al. 2006)

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

– ““Naked-eye GRB”: GRB 080319BNaked-eye GRB”: GRB 080319B– First shock breakout from stellarFirst shock breakout from stellar

surface: GRB 060218 / SN2006ajsurface: GRB 060218 / SN2006aj– Short GRBs with large and small redshiftsShort GRBs with large and small redshifts

Arcsecond localizations => evidence for compact mergersArcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitorsNew data hints at subclasses in redshift, offset, and progenitors

– Nearby long GRBs with and without SNeNearby long GRBs with and without SNe Possible new classes of GRBsPossible new classes of GRBs

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Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– > 240 GRBs with arcsec positions> 240 GRBs with arcsec positions– ~ 100 GRBs with redshifts~ 100 GRBs with redshifts– 80% of world X-ray afterglows80% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares Jet breaks (or not…)Jet breaks (or not…)

– ““Naked-eye GRB”: GRB 080319BNaked-eye GRB”: GRB 080319B– First shock breakout from stellarFirst shock breakout from stellar

surface: GRB 060218 / SN2006ajsurface: GRB 060218 / SN2006aj– Short GRBs with large and small redshiftsShort GRBs with large and small redshifts

Arcsecond localizations => evidence for compact mergersArcsecond localizations => evidence for compact mergers New data hints at subclasses in redshift, offset, and progenitorsNew data hints at subclasses in redshift, offset, and progenitors

– Nearby long GRBs with and without SNeNearby long GRBs with and without SNe Possible new classes of GRBsPossible new classes of GRBs

– Metallicities of star forming regions in galaxiesMetallicities of star forming regions in galaxiesto record high redshift (z=6.3) using GRBsto record high redshift (z=6.3) using GRBs

Includes transitions never before seenIncludes transitions never before seen

GRB 050730 at z=3.97(Chen et al. 2005)

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Short GRBsShort GRBs

Major discovery of Swift is Major discovery of Swift is the first localizations of the first localizations of short GRBs, and the short GRBs, and the discovery that they occur discovery that they occur in different environments in different environments than long GRBsthan long GRBs

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

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GRB ClassificationGRB Classification

• Bimodal distribution of durations- Short, hard GRBs: mergers- Long, soft GRBs: collapsars

Short Bursts: mergersOld (few billion yrs)Outside galaxies

Long Bursts: collapsarsYoung (few million yrs)Star-forming regions

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~35 Short GRBs (33 from Swift BAT)~35 Short GRBs (33 from Swift BAT)

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GRB 050509BGRB 050509B

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?

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

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GRB050709: Second Short GRB GRB050709: Second Short GRB AfterglowAfterglow

•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

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GRB 050724GRB 050724

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 Mo/yr.

Another old, nearby elliptical galaxy associated with a short GRB!!

t90 = 1 s by BATSE definition. (But long soft tail.)

30x brighter than GRB 050509B.

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GRB 050724GRB 050724

No evidence of jet break,θj > 0.5 rad for reasonable jet parameters

t-0.8

Late-time bump (~1/2 day)

Grupe et al. 2006

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~30 photons

t-2.05

GRB 050813GRB 050813

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Possible association with elliptical galaxies in cluster at z~ 0.722 (or 1.8 – Berger)

GRB 050813GRB 050813

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Swift Short GRBs without Swift Short GRBs without afterglowsafterglows

•GRB 050906:• t90 = 0.13 s• XRT observations began at T+79 s• No X-ray counterpart – very unusual

•GRB 050925 (short, soft)• t90 = 0.07 s• XRT observations began at T+92 s• No X-ray counterpart – very unusual

•GRB 051105A• t90 = 0.03 s• XRT observations began at T+68 s• No X-ray counterpart – very unusual

•GRB 051114• t90 = 2.2 s• XRT observations began at T+126 ks• No X-ray counterpart

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GRB 051210GRB 051210

t-2.57

flare

No clear optical counterpart or redshift, but near z=0.114 cluster

Mangano et al. 2006

Naked GRB

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Many small flares

Energy injection

t-1.49

GRB 060313GRB 060313

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• 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 060313GRB 060313

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Long vs short GRB energeticsLong vs short GRB energetics

060614

Long GRBs, from Panaitescu 2005)

short GRBs

long GRBs

1055

1054

1048

1053

1052

1049

1050

1051

1047

10-2 10-1 100 101 102 103

T90 / (1+z) (s)

Eis

o (e

rg)

Swift GRBs

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Fundamental questions on short GRBsFundamental 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?

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Short GRB Environments: “normal” Short GRB Environments: “normal” decaysdecays

t-1.15

t-1.22

t-1.13

050509B

t-1.07

051227 060121 (HETE-2)

060502B

t-1.2

060505

• ~ 25% of sample• No evidence for decay of prompt emission => consistent with short duration of bursts

-exception: 051227, 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

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Short GRB Environments: “canonical Short GRB Environments: “canonical afterglows”afterglows”

t-2.3

t-1..9

060614 061006061201

t-1.5

t-0.5

t-2.2t-0.1

t-0.7

t-1.8

t-1.49

060313

t-1.49

050724

t-0.8

t-1.20

t-1.93051221A

t-1.20

• ~ 25% of sample• Evidence for decay of prompt emission in 3 bursts: 050724, 060614, 061006.

- 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)

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Short GRB Environments: “Naked” Short GRB Environments: “Naked” GRBsGRBs

t-2.05 t-2.57

050813 051210

t-5.8

060801

t-1.2

061210

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: 050906, 050925, 051105A, 051114, 070209, 070810B,

070923, 071112B, 080121

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Short GRB SummaryShort GRB Summary

X-ray afterglows similar to long GRBs, but fainter and X-ray afterglows similar to long GRBs, but fainter and less complexless complex

Late central engine activity implied by flares and Late central engine activity implied by flares and energy injection in X-ray afterglowsenergy injection in X-ray afterglows

High incidence of naked GRBs => low density High incidence of naked GRBs => low density environmentsenvironments

““Missing” hostsMissing” hosts– Ejections from hosts?Ejections from hosts?– High redshift?High redshift?

Possible subclasses:Possible subclasses:– Extended soft tailsExtended soft tails– Late central engine activityLate central engine activity

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GRB ClassificationGRB Classification

Horvath et al. 2002, AA, 392, 791

Donaghy et al. 2006

Short/hard

Long/soft

E. Nakar, 2006

Gehrels et al. 2006

The problem with GRBs is that we have The problem with GRBs is that we have no clear-cut emperical classification no clear-cut emperical classification scheme:scheme:– Considerable overlap in durations and Considerable overlap in durations and

spectral properties between the spectral properties between the “long” and “short” populations“long” and “short” populations

– Increasing sample of “short/hard” Increasing sample of “short/hard” GRBs with long soft tails (~ 33%)GRBs with long soft tails (~ 33%)

050709, 050724, 051227, 060121, 050709, 050724, 051227, 060121, 061006, 061210, 070714B, 080123, 061006, 061210, 070714B, 080123, 080503080503

These often have t90 >> 5s as These often have t90 >> 5s as measured by Swift/BATmeasured by Swift/BAT

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Long Soft Tails of Short GRBsLong Soft Tails of Short GRBs

Norris & Bonnell 2006, ApJ, 643, 266 Villasenor et al. 2005, Nature, 437, 855

GRB 050709

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Long Soft Tails of Short GRBsLong Soft Tails of Short GRBs

Barthelmy et al. 2005, Nature, 438, 994

GRB 050724GRB 051227

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GRB060505GRB060505

• Weak burst that did not trigger BAT• Ground processing revealed weak source• Late notification and slew• t90 = 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.

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GRB060614GRB060614

• Duration: tDuration: t9090 = 102s => “long”/Type II = 102s => “long”/Type II

• Initial hard pulse with longer soft tail: Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs similar to several “short”/Type I GRBs (though tail is brighter, harder, and (though tail is brighter, harder, and more variable in this case)more variable in this case)

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GRB060614GRB060614

Gal-Yam et al., Nature

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Gehrels et al. 2006, Nature

GRB060614GRB060614

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Zhang et al. 2007, ApJ, submitted

GRB060614GRB060614

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The enigmatic case of GRB 060614The enigmatic case of GRB 060614

The problem with GRBs is that we have no clear-cut emperical classification The problem with GRBs is that we have no clear-cut emperical classification scheme:scheme:– Considerable overlap in durations and spectral properties between the “long” Considerable overlap in durations and spectral properties between the “long”

and “short” populationsand “short” populations– Increasing sample of “short/hard” GRBs with long soft tailsIncreasing sample of “short/hard” GRBs with long soft tails

050709, 050724, 051227, 060121, 061006, 061210050709, 050724, 051227, 060121, 061006, 061210 These often have tThese often have t9090 >> 5s as measured by Swift/BAT >> 5s as measured by Swift/BAT

– Case of GRB 060121 (Donaghy et al.) => argument for multidimensional Case of GRB 060121 (Donaghy et al.) => argument for multidimensional classification, new terminology (“short/long population GRBs”)classification, new terminology (“short/long population GRBs”)

– Case of GRB 060614 => suggestion for Type I/Type II classification (Zhang et al Case of GRB 060614 => suggestion for Type I/Type II classification (Zhang et al 2007, ApJ; Zhang 2006, Nature)2007, ApJ; Zhang 2006, Nature)

Duration: tDuration: t9090 = 102s => “long”/Type II = 102s => “long”/Type II Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs

(though tail is brighter and more variable in this case)(though tail is brighter and more variable in this case) Location: outskirts of host galaxy => “short”/Type ILocation: outskirts of host galaxy => “short”/Type I Lack of SN => short/Type I or unusual “long”/Type IILack of SN => short/Type I or unusual “long”/Type II Lag-luminosity relation: small lag => “short”/Type ILag-luminosity relation: small lag => “short”/Type I EEisoiso ~ 10 ~ 105151 ergs, E ergs, Eγγ ~ 4 x 10 ~ 4 x 104949 ergs ergs

=> intermediate between Type I and Type II=> intermediate between Type I and Type II

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Keck Spectroscopy of GRB 050505

Berger et al. 2005

Metallicity vs Redshift

z = 4.275Damped Ly- N(HI)=1022 cm-2

- n ~ 102 cm-3

- Z = 0.06 ZO

- Mprogenitor < 25 MO

..

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Subaru spectrum of GRB 050904: z = 6.295 ± 0.002

Kawai et al. 2006

NH=4E21

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The Future of SwiftThe 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 In the next 3-4 years we will obtain – more high redshift GRBsmore high redshift GRBs– more GRBs with good optical observations, more GRBs with good optical observations, – more short GRBs, and more short GRBs, and – more unusual cases (like 061007, 060614, 070110, …)more unusual cases (like 061007, 060614, 070110, …)

Starting subthreshold trigger experiment to search for weak bursts Starting subthreshold trigger experiment to search for weak bursts in the noisein the noise

GLAST / Swift synergyGLAST / Swift synergy– GBM: will provide MeV-range spectral data for many Swift GRBsGBM: will provide MeV-range spectral data for many Swift GRBs– LAT: will discover very high energy (GeV) GRBs that can be localized by LAT: will discover very high energy (GeV) GRBs that can be localized by

Swift (~ 1 / month)Swift (~ 1 / month) Investigating possibility of rapid Swift responses to LAT GRBsInvestigating possibility of rapid Swift responses to LAT GRBs

Enhanced LIGO (2009)Enhanced LIGO (2009)– Will double detection range, may permit detection of inspiral sirensWill 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 Simultaneous detection of short GRB by Swift and LIGO would provide

“smoking gun” for merger picture“smoking gun” for merger picture– NS-NS inspiral out to 300 Mpc – up to 3/dNS-NS inspiral out to 300 Mpc – up to 3/d– NS-BH inspiral to 650 MpcNS-BH inspiral to 650 Mpc

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Long-Term FutureLong-Term Future

Beyond Beyond SwiftSwift: the high z universe: the high z universe– Swift may be detecting high z bursts, but ground-Swift may be detecting high z bursts, but ground-

based observations are required to identify thembased observations are required to identify them

– SVOMSVOM

– JANUSJANUS: identify high z GRBs and QSOs: identify high z GRBs and QSOs ReionizationReionization Star formation at high zStar formation at high z

– XeniaXenia: High resolution spectroscopy of GRBs: High resolution spectroscopy of GRBs ReionizationReionization First starsFirst stars Cosmic StructureCosmic Structure WHIMWHIM

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JANUSJANUS

SMEX mission selected for Phase A studies (launch in mid-SMEX mission selected for Phase A studies (launch in mid-2012)2012)

X-ray Flash Monitor (0.5-20 keV) + NIR Telescope (0.7-1.7 X-ray Flash Monitor (0.5-20 keV) + NIR Telescope (0.7-1.7 μμm, m, R=14)R=14)– Optimized for detection and identification of high-z GRBsOptimized for detection and identification of high-z GRBs– > 50 GRBs with 5 < z < 12> 50 GRBs with 5 < z < 12

Star formation rate, finder for ground-based followupStar formation rate, finder for ground-based followup

– 20,000 sq degree spectroscopic sky survey to discover 20,000 sq degree spectroscopic sky survey to discover

> 400 QSOs @ 6 < z < 10> 400 QSOs @ 6 < z < 10

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XeniaXenia

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

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XeniaXenia

Xenia

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SummarySummary

SwiftSwift has compiled a large database of bursts and their has compiled a large database of bursts and their X-ray and optical afterglows, discoveringX-ray and optical afterglows, discovering– Complex X-ray afterglowsComplex X-ray afterglows– X-ray flares, implying long-lived central engine activityX-ray flares, implying long-lived central engine activity– Prompt, accurate localization of short GRBs -> mergersPrompt, accurate localization of short GRBs -> mergers– Bright, high-z burstsBright, high-z bursts

SwiftSwift has increasingly become the satellite of choice for has increasingly become the satellite of choice for multiwavelength, rapid-response Targets of Opportunitymultiwavelength, rapid-response Targets of Opportunity– CVs and novaeCVs and novae– SNeSNe– Galactic transientsGalactic transients– AGN and blazarsAGN and blazars

Future prospects:Future prospects:– Swift/GLASTSwift/GLAST synergy synergy– Swift/LIGOSwift/LIGO synergy -> compact mergers synergy -> compact mergers– JANUSJANUS, , SVOMSVOM, and other proposed missions will focus on , and other proposed missions will focus on

high-zhigh-z