X-ray Afterglows of Gamma-ray Bursts

David BurrowsThe Pennsylvania State UniversitySwift X-Ray Telescope PI

Fireball model: synchrotron emission from power-law distribution of electrons in highly relativistic outflows

GRB afterglowsGRB afterglows

E ~ 1053 ergs

T = 0 s

R = 106 cm

Pre-Burst

Burst

Afterglow

ShockFormation

Γ ~ 103

T ~ 102 sR = 3 x 1012 cm

T ~ 3 x 103 sR = 1014 cm

R = 3 x 1016 cmT ~ 106 s

γ, X

γ, X

X, optical, radio

LOC

AL

MED

IUM

GRBs and SwiftGRBs and Swift

20 November 2004

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 6 UV/optical broad-band

filtersfilters– 2222ndnd mag sensitivity mag sensitivity

(filtered)(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

All Swift data are immediately publichttp://swift.gsfc.nasa.gov/sdc/

Swift GRBs (> 440 so far)Swift GRBs (> 440 so far)

Short GRB

Short GRB

FRED

Fast Rise Exponential Decay

90% followed up with XRT observations

Swift X-ray AfterglowsSwift X-ray Afterglows> 370 Prompt X-ray LCs

GRB 060204B GRB 060211A GRB 060306

GRB 060413 GRB 060428A GRB 060502A

GRB 060510A GRB 060510B GRB 060729

1e2 1e6

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– ~90% of world X-ray afterglows~90% of world X-ray afterglows

Complex X-ray lightcurves and flaresComplex X-ray lightcurves and flares

GRB 071227(D’Avanzo et al. 2007)

VLT

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– 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…)

– 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

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– 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…)

– 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

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

Key Swift DiscoveriesKey Swift Discoveries

GRBsGRBs– 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…)

– First shock breakout from stellarFirst shock breakout from stellarsurface: 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=8.2) using GRBsto record high redshift (z=8.2) using GRBs

Includes transitions never before seenIncludes transitions never before seen

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

z=6.7

0

12

34

Vaughan et al. 2005

t -0.4

t -0.7

-0.730.11

t -5.2

-1.90.9

Zhang et al. 2006, ApJ, 642, 354

t -(2+β) ~ t

-3 (Kumar & Panaitescu 2000)

Emergence of afterglow

Canonical LC: GRB 050315Canonical LC: GRB 050315

X-ray FlaresX-ray Flares

Burrows et al. 2005, Science, 309, 1833Romano et al. 2006, A&A, 450, 59Falcone et al. 2006, ApJ, 641, 1010Liang et al. 2006, ApJ, 646, 351Burrows et al. 2006, X-ray Universe (ESA SP-604), 877Guetta et al. 2007, AIP Conf. Proc., 924, 17Chincharini et al. 2007, ApJ, 671, 1903Falcone et al. 2007, ApJ, 671, 1921Kocevski, Butler, & Bloom 2007, ApJ, 667, 1024Morris, D. 2008, PhD thesis

GRB 050730

X-ray FlaresX-ray Flares

3x

X-ray FlaresX-ray Flares

• ~ ½ of bursts have X-ray flares

• typical time scale ~ hundreds of seconds

Power law slope ~ -1.1

Width distribution of flaresWidth 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.

Flare rise and fall timesFlare rise and fall times

Mechanisms:1) Ambient density fluctuations2) Patchy shell3) Refreshed shocks4) 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.

Flare MechanismsFlare Mechanisms(D. Morris, PhD thesis, 2008)(D. Morris, PhD thesis, 2008)

Compare each flare to Compare each flare to required characteristics of required characteristics of several modelsseveral models

– Reverse Shock IC: 1Reverse Shock IC: 1– Cloud Model I: 0Cloud Model I: 0– Cloud Model II: 3Cloud Model II: 3– Internal Shocks: 11Internal Shocks: 11– Afterglow Onset: 1Afterglow Onset: 1– Energy Injection: 3Energy Injection: 3

Implies IS most likely model Implies IS most likely model for any particular flare, but for any particular flare, but likely need several models likely need several models to explain the entire to explain the entire collection of GRB X-ray collection of GRB X-ray flaresflares

X-ray Flare MechanismX-ray Flare Mechanism

Internal Shocks?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 Spectral evolution of flares consistent with spectral

evolution of prompt pulsesevolution 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” Examination of post-flare decay slopes suggests that “clock” is reset at beginning of each flareis 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 Requires late-time activity of central engine => central

engine restarts as late at 10engine restarts as late at 1044 s after burst. s after burst.

Upscattered emission?Upscattered emission? Panaitescu (2008, MNRAS, 383, 1143)Panaitescu (2008, MNRAS, 383, 1143)

Plateau PhasePlateau Phase

GRB 060729

Plateau phase

~ 40 ks

Plateau PhasePlateau Phase

Thought to be energy injection into the Thought to be energy injection into the external shock, either byexternal shock, either by1.1. Delayed impacts of slower shocks created at the Delayed impacts of slower shocks created at the

time of the burst, ortime of the burst, or

2.2. Late-time ejection of relativistic shells from the Late-time ejection of relativistic shells from the central engine central engine

Difficult to distinguish between these alternatives Difficult to distinguish between these alternatives in most cases.in most cases.

Rapid decline

Small flare

Plateau

???

t-9

Troja et al. 2007, ApJ, 665, 599

The Plateau of GRB 070110The Plateau of GRB 070110

Plateau PhasePlateau Phase

Troja et al. 2007, ApJ, 665, 599

Comparison with GRB 050904:Comparison with GRB 050904:

Plateau PhasePlateau Phase

Other recent examples:Other recent examples:

Plateau PhasePlateau Phase

Other recent examples:Other recent examples:

Plateau PhasePlateau Phase

Drop-offs:Drop-offs: Steep decline cannot be caused in external Steep decline cannot be caused in external

shockshock Requires long-lived central engine activityRequires long-lived central engine activity Could be explained by magnetar spin-down in Could be explained by magnetar spin-down in

some casessome cases

Plateau PhasePlateau Phase

Drop-offs:Drop-offs: Steep decline cannot be caused in external Steep decline cannot be caused in external

shockshock Requires long-lived central engine activityRequires long-lived central engine activity Could be explained by magnetar spin-down in Could be explained by magnetar spin-down in

some casessome cases

Other Possibilities:Other Possibilities: Recovery from intense photohadronic phase that Recovery from intense photohadronic phase that

depletes internal GRB blast wave energy: depletes internal GRB blast wave energy: Dermer (2007, ApJ, 664, 384)Dermer (2007, ApJ, 664, 384)

Up-scattered FS emission: Panaitescu (2008)Up-scattered FS emission: Panaitescu (2008)− May help explain chromatic breaksMay help explain chromatic breaks

GRB 090709GRB 090709

BAT/XRT lightcurveBAT/XRT lightcurve

GRB 090709GRB 090709

XRT lightcurveXRT lightcurve

GRB 090709GRB 090709

BAT power spectrumBAT power spectrum– confirmed by K-W and INTEGRAL SPI-APS, Suzaku confirmed by K-W and INTEGRAL SPI-APS, Suzaku

WAMWAM

Markwardt et al. 2009, GCNC 9645

P = 8.06 sQ ~ 11p ~ 10-6

GRB 090709GRB 090709

Very bright burst: F~ 2.6e-5 ergs/cmVery bright burst: F~ 2.6e-5 ergs/cm22 (Sakamoto et (Sakamoto et al., GCNC 9640)al., GCNC 9640)

Afterglow detected in H, K, not in J => z > Afterglow detected in H, K, not in J => z > 8.5 ??? 8.5 ??? (Aoki et al., GCNC 9634; Morgan et al., GCNC (Aoki et al., GCNC 9634; Morgan et al., GCNC 9635)9635)– But, reports of very early marginal detections in r’ But, reports of very early marginal detections in r’

suggest low redshift (Cenko et al., GCNC 9646)suggest low redshift (Cenko et al., GCNC 9646)

– NNHH measured by XRT suggests low redshift (Butler et al., measured by XRT suggests low redshift (Butler et al., GCNC 9639; Rowlinson et al., GCNC 9642)GCNC 9639; Rowlinson et al., GCNC 9642)

No galaxy found in deep optical obs (i’ > 25.2, No galaxy found in deep optical obs (i’ > 25.2, 10.4m GTC) 10.4m GTC) (Castro-Tirado et al., GCNC 9655)(Castro-Tirado et al., GCNC 9655)– Nondetection of host galaxy, 8 s QPO, high b (20Nondetection of host galaxy, 8 s QPO, high b (2000) and ) and

high Nhigh NHH suggest Galactic magnetar suggest Galactic magnetar

No radio detection by WSRT or VLANo radio detection by WSRT or VLA

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

GRB 090423: z=8.2GRB 090423: z=8.2– 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, …)

GRB 090709: QPO ???GRB 090709: QPO ???

FermiFermi / / SwiftSwift synergy 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

SwiftSwift

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

Short GRBsShort GRBs

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

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

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

GRB 050724GRB 050724

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

30x brighter than GRB 050509B. (6E-7 ergs/cm2)

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 Mo/yr.

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

GRB 050724GRB 050724

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

30x brighter than GRB 050509B. (6E-7 ergs/cm2)

Slewed in 75 s. Very odd X-ray lightcurve.

No evidence of jet break,θj > 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

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

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 has increasingly become the satellite of choice for multiwavelength, rapid-response Targets of for multiwavelength, rapid-response Targets of OpportunityOpportunity– CVs and novaeCVs and novae– SNeSNe– Galactic transientsGalactic transients– AGN and blazarsAGN and blazars– http://www.swift.psu.edu/too.htmlhttp://www.swift.psu.edu/too.html

Future prospects:Future prospects:– Swift/FermiSwift/Fermi 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