Short Bursts

Short Bursts

Daniel PerleyAstro 250

9 November 2005

Long BurstsGRB Classes

Daniel Perley 9 November 2005Short Bursts

GRBs have long been known to fall into two general categories:

time (seconds)

coun

t rat

e (c

t/s)

45 s

l o n g b u r s t

Classes of GRBs Long Bursts Short Bursts Durations Duration vs. Hardness Duration vs. Fluence

Short Bursts before Swift Long Burst Localization Short Burst Localization Afterglow Nondetections Galaxy Correlations

Short Burst Models Primordial Black Holes Magnetar Giant Flare NS-NS Merger NS-BH Merger Collapsar Summary

Short Bursts since Swift GRB050509B GRB050709 GRB050724 GRB050813 GRB050906 GRB050925 GRB051103 GRB051105A Summary

Conclusions

Short BurstsGRB Classes

Daniel Perley 9 November 2005

time (seconds)

coun

t rat

e (c

t/s)

short burst0.8 s

GRBs have long been known to fall into two general categories:

Short Bursts





Conclusions

Burst DurationsGRB Classes


T90 (seconds)

N

The separate populations are statsitcally robust, although intersecting.

10-110-2 1 10 100 1000

Short Bursts





Conclusions

Burst DurationsGRB Classes


T90 (seconds)

N

10-110-2 1 10 100 1000

The separate populations are statsitcally robust, although intersecting.

short bursts

l o n g b u r s t s

Short Bursts





Conclusions

Duration/HardnessGRB Classes


T90 (seconds)

The two populations have different hardnesses:

Har

dnes

s (S

3/S2)

short bursts

l o n g b u r s t s

Short Bursts





Conclusions

Duration/FluenceGRB Classes


Other intrinsic differences have also been noticed.

T90 (seconds)10-110-2 1 10 100 1000

F tot (e

rg/c

m2 )

10-8

10-7

10-6

10-5

10-4

Figure 1, Balasz et al. 2004

l o n g b u r s t s

short bursts

Short Bursts





Conclusions

Long Burst Localization


First GRB (long burst) localized and first host identified in 1997. Many have followed since then.

• All long GRBs located in star-forming galaxies

• All long GRBs located in regions with massive stars

• Coincident type Ic supernova observed in one case

→ Long bursts are associated with supernovae.

However, short GRBs long eluded localization, and no similar conclusions could be made.

Short Bursts

Before SwiftClasses of GRBs Long Bursts Short Bursts Durations Duration vs. Hardness Duration vs. Fluence




Conclusions

Short Burst Localization


The intrinsically short duration of a short burst makes determining the position of the prompt gamma emission even more difficult than usual.

"Best" localizations (5-50 square arcmin) generally from Interplanetary Network.

Short Bursts

5 '

Before SwiftClasses of GRBs Long Bursts Short Bursts Durations Duration vs. Hardness Duration vs. Fluence




Conclusions

Afterglow NondetectionsBefore Swift


Before thist year, no short burst afterglow had been found in any IPN or burst detection error box.

Short Bursts

1 = 000607 5.6 arcmin2

2 = 001025B 24.5 arcmin2

3 = 001204 6 arcmin2

4 = 010119 3.3 arcmin2

= long burst detected

= long burst limit





Conclusions

Galaxy CorrelationsBefore Swift


(Recent) study computes correlation function of BATSE short burst positions with nearby galaxies.

Short Bursts

Result: correlation significant to 2σ

No correlation seen for long bursts.

Estimate of 5-25% of GRBs from <100 Mpc





Conclusions

Burst ModelsBurst Models


A large number of models had been proposed – mostly of the same which had been previously proposed for GRBs in general.

• Black hole evaporation• SGR (magnetar) giant flares• Neutron star – neutron star mergers• Neutron star – black hole mergers• Collapsar• Neutron star collapse (supranova)

Short Bursts





Conclusions

Primordial Black HolesBurst Models


An early suggestion: GRBs may be the evaporation of black holes produced in the early universe.

T90 (seconds)

N

10-110-2 1 10 100 1000

Mass: 7 × 1014 g (mc2 = 5 × 1035 erg)

→ Distance: ~few parsecs

Burst duration: <50-200 ms

cannot explain most short bursts

Short Bursts





Conclusions

Magnetar Giant FlareBurst Models


Massive flare on the surface of highly magnetized neutron star.

Catastrophic magnetic field reorganization.

Some previous flares:

- 5 March 1979 event: 4 × 1044 ergs (SGR 0526-66, LMC) 0.2 s

- 27 August 1998 event: 8 × 1043 ergs (SGR 1900+14) 0.2 s

Duration and hardness consistent with short GRBs.

Distance for GRB: 4 Mpc (Virgo cluster: 20 Mpc)

But could there be much larger flares?

Short Bursts





Conclusions





- 27 December 2004 event 2 × 1046 ergs (SGR 1806-20) 0.5 s

0.8 erg/cm2 over 0.5s

Most energetic Galactic event since Tycho.

Sirius: 10-4 erg/cm2/sFull Moon: 1 erg/cm2/s

Short Bursts





Conclusions





- 27 December 2004 event 2 × 1046 ergs (SGR 1806-20) 0.5 s

Duration and hardness consistent with short GRBs.

(long ringing 'tail' would not be detectable at great distance)

Distance for GRB: 30 Mpc (Virgo cluster: 20 Mpc)

Magnetars all young: ~104 year lifetime (restricted to star-forming galaxies/regions)

Repetition possible over long time scales

Short Bursts





Conclusions

Neutron Star-Neutron Star MergerBurst Models


Gravitational binding energy:

~ 1053 erg

→ Mpc/Gpc distances

Timescale for collapse: <~1 second

Closely orbiting neutron stars (d ~< solar radius) lose energy from gravitational radiation.

Systems known to exist (binary pulsars)

Must eventually merge.

Post-merger object quickly collapses to black hole

Very high angular momentum of system : accretion disk forms; falls onto black hole.

Short Bursts

G M2

R





Conclusions

Neutron Star-Black Hole MergerBurst Models


Gravitational binding energy: MNSc2 ~ 1054 erg

→ Mpc/Gpc distances

Timescale for accretion: <~1 second

Closely orbiting neutron star / black hole pair also loses energy to gravitational radiation and merges.

Neutron star is tidally disrupted into accretion disk; falls onto black hole.

Short Bursts





Conclusions

Supernovae can 'kick' binary out of Galaxy.

Compact Object MergersBurst Models


Either type of merger:

Inspiral takes ~ 1 Gyr.

• Star formation may have ceased.

• System may have migrated from point of origin – supernova explosions cankick the binary well outside galacticinterior

Possibility of "mini-supernova" due to production of radioactive elements in ejected matter.

Short Bursts





Conclusions

CollapsarBurst Models


Collapsar (hypernova) model highly successful in describing long bursts.

Collapse of iron core of highly massive star to black hole + accretion of material (0.1-5 Msun).

Relativistic jet penetrates stellar envelope

Energies ~ 1050 erg : cosmological distances

Fallback time for stellar core: ~few seconds too slow for short GRBs.

Significant uncertanties in calculation; Breakout flash could be shorter?

Massive stars short-lived: would be bound to star-forming regions (like long GRBs)

Short Bursts





Conclusions

Model SummaryBurst Models


PBH giant flare merger collapsarEnergy (erg) 1036 1046 ~1050 >1050

Distance scale pc Mpc Gpc Gpc

Timescale too short OK OK too long?

Progenitor mini-BH young NS old NS binary

short-lived star

Environment Galaxy star-forming galaxies

in/near all types of galaxies

star-forming galaxies

Signatures possibility of repeat

possible mini-SN

type Ib/Ic supernova

Short Bursts





Conclusions

GRB 050509BThe Swift Era


First Swift short burst.

First X-ray afterglow: XRT provided 2.8' localization

This position is very close to large elliptical at center of low-z cluster.

XRT

Large ellipticalz = 0.2248

blue

T90 = 0.040

S = 1 × 10-10

E = 3 × 1048





Conclusions

all units CGS



Is the burst associated with the elliptical?

Chance alignment probability very small.

inside galaxy cluster: 3% within 45" of center: 0.07%

(no long GRB ever seen in a cluster)

XRT

Large ellipticalz = 0.2248

blue

40 kpc

T90 = 0.040

S = 1 × 10-8

E = 3 × 1048





Conclusions



Is the burst associated with the elliptical?

Chance alignment probability very small.

inside galaxy cluster: 3% within 45" of center: 0.07%

(no long GRB ever seen in a cluster)

T90 = 0.040

S = 1 × 10-8

E = 3 × 1048





Conclusions

Additional arguments:

• Extremely short duration even for short GRBs – putting at high redshift (z~2) requires unrealistically short intrinsic duration.

• Energetics of putting at high-z similarly difficult for very short durations.



No counterpart seen at other wavelengths.

Cannot be a supernova (if in cluster).

No mini-supernova observed.

T90 = 0.040

S = 1 × 10-8

E = 3 × 1048





Conclusions

SNIapeak

GRB 050709The Swift Era


HETE-II short burst.

X-ray afterglow seen. Unambiguously in low-z galaxy.

Optical transient (first ever for short GRB) detected coincident with X-ray position.

XRT

HST Transient

Star-forming irregularz = 0.160

3.8 kpc

T90 = 0.070

S = 3 × 10-7

E = 2 × 1049





Conclusions



Optical light curve: power-law decay with jet break (like long burst – no supernova bump)

T90 = 0.070

S = 3 × 10-7

E = 2 × 1049





Conclusions

X-ray

Optical

Radio



Optical and radio (first for short GRB) transients seen. Unambiguously associated with non star-forming galaxy (within last Gyr) at low-z.

Not in a cluster.

Transient

Early-typez = 0.258

XRT

2.6 kpc

T90 = 3

S = 6 × 10-7

E = 1 × 1050





Conclusions



X-ray afterglow, but no optical/radio transient.

Inside a cluster - numerous possible hosts.

XRT

Ellipticalz = 0.719

Ellipticalz = 0.73

Ellipticalz = 0.722

T90 = 0.6

S = 6 × 10-7

E = 1 × 1050





Conclusions



No X-ray afterglow detected.

BAT position consistent with IC 326.

BAT IC 326 z = 0.0308

IC 327

p ~ 0.1%

T90 = 3

S = 6 × 10-8

E = 1 × 1047

at 133 Mpc





Conclusions



Soft, thermal spectrum.

Galactic latitude: b = - 0.1°

Strong radio source – no optical or X-ray detections.

SGR flare ('new' SGR)

T90 = 0.13

S = 8 × 10-8

E = 1 × 1040

at 20 kpc





Conclusions



IPN detection of bright short GRB. Consistent with outer regions of M81.

M 81Sb z = 0

M 82Irr z = 0p ~ 0.5%

T90 = 0.17

S = 2 × 10-5

E = 5 × 1046

at 4 Mpc (M81) ~ 1051

at 500 Mpc





Conclusions

GRB 051105AThe Swift Era


No X-ray afterglow detected.

BAT

T90 = 0.13

S = 2 × 10-8

E = ?





Conclusions

Recent Short BurstsThe Swift Era


redshift host trans most likely origin

050509B 0.2248 E (cl) 3 × 1048 X NS-NS/BH merger

050709 0.160 Irr 2 × 1049 XO NS-NS/BH merger

050724 0.258 early 1 × 1050 XOR NS-NS/BH merger

050813 0.72 E (cl) 2 × 1050 X NS-NS/BH merger

050906 0.031? S 1 × 1047 giant flare?

050925 Galaxy ~ 1040 large SGR flare

051103 0? Sb? 5 × 1046 giant flare?

051105A ? ?

energy (erg)





Conclusions

ConclusionsThe Swift Era


• Most short bursts are due to compact object mergers.

• Short bursts are beamed.• Some short bursts may be due to magnetar

giant flares in other galaxies, but a definitive example is still lacking.

• Short bursts occur more frequently per volume than long bursts (or are beamed less), but are intrinsically fainter.





Conclusions

Short Bursts

Documents

Transcript of Short Bursts