grb 060121: implications of a short-burst at high redshift

GRB 060121:GRB 060121:Implications of a short-burstImplications of a short-burst

at high redshiftat high redshift

Antonio de Ugarte PostigoAntonio de Ugarte Postigo

Instituto de Astrofísica de Andalucía (IAA-CSIC)Instituto de Astrofísica de Andalucía (IAA-CSIC)

Granada, SpainGranada, Spain

RingbergRingberg, 28th March 2007, 28th March 2007

ContentsContents IntroductionIntroduction First Short GRBsFirst Short GRBs

First observationsFirst observations Initial thoughtsInitial thoughts

GRB 060121GRB 060121 ObservationsObservations Redshift estimationRedshift estimation Host galaxyHost galaxy Implications of a high-z eventImplications of a high-z event

Further observationsFurther observations Conclusions and future workConclusions and future work

Antonio de Ugarte Postigo, Antonio de Ugarte Postigo, RingbergRingberg, 28th March, 28th March20072007

CharacterisiticsCharacterisitics of short GRBs of short GRBs

DurationDuration HardnessHardness Soft X-ray tailSoft X-ray tail Spectral lagsSpectral lags

(Tingfeng et al. 2006)

(Nakar et al. 2007)

(Villaseñor et al. 2005)

•Introduction•First SGRBs•GRB 060121•Further obs•Conclusions


(Nakar et al. 2007)

First observations of short GRBsFirst observations of short GRBsGRB 050509BGRB 050509B

First short burstFirst short burstprecisely localizedprecisely localized((SwiftSwift))

A giant elliptical onA giant elliptical onthe edge of the errorthe edge of the errorboxbox

No counterpartNo counterpartdetecteddetected

No supernovaNo supernova(Castro-Tirado et al. 2005)

(Hjorth et al. 2005)

Antonio de Ugarte Postigo, Antonio de Ugarte Postigo, RingbergRingberg, 28th March, 28th March20072007•Introduction

•First SGRBs•GRB 060121•Further obs•Conclusions

The first afterglow:The first afterglow:GRB 050709GRB 050709

First counterpart.First counterpart. Embedded in its hostEmbedded in its host

galaxy.galaxy. Limited photometricLimited photometric

information (detectedinformation (detectedmore than 1 day aftermore than 1 day afterthe burst)the burst)





Defining the typical afterglowDefining the typical afterglowGRB 050724 & GRB 051221AGRB 050724 & GRB 051221A

The first afterglows were found embedded inThe first afterglows were found embedded innearby, bright hostsnearby, bright hosts

Several orders of magnitude fainter than long GRBsSeveral orders of magnitude fainter than long GRBs

(Beger et al. 2005)

(Soderberg et al. 2005)



Host galaxiesHost galaxies

Dominant stellar population older than long GRBsDominant stellar population older than long GRBs More varied types of galaxies E, More varied types of galaxies E, SbSb, S0, S0……

GRB 050509B GRB 050709 GRB 050724 GRB 051221A



Conclusions of the first observationsConclusions of the first observations

Coalescence of aCoalescence of acompact binary systemcompact binary system(NS-NS or NS-BH)(NS-NS or NS-BH)

Fainter than longFainter than longGRBsGRBs(10(1048-5148-51 erg) erg)

Happening in the nearHappening in the nearUniverse z < 0.5Universe z < 0.5

No SN componentNo SN component



GRB 060121: GRB 060121: γγ-Ray detection-Ray detection

Detected by Detected by HETE-2HETE-2 Also observed byAlso observed by

KONUS/KONUS/Wind Wind and and SwiftSwift TT90 90 = 1.97 = 1.97 ± 0.06± 0.06 s s EEpp= 120 = 120 ± 7 ± 7 keVkeV Classified as a short-Classified as a short-

hard burst (Boer et al.hard burst (Boer et al.2006).2006).



Optical and Optical and nIRnIR observations observations

Triggered 1.5m OSNTriggered 1.5m OSNstraight away.straight away.

First detection obtainedFirst detection obtainedin I band 22 min after thein I band 22 min after theburst onset.burst onset.

Additional observationsAdditional observationsin U, B, V, R, I and Kin U, B, V, R, I and Kduring the next 5 daysduring the next 5 daysfrom:from: 1.5m OSN1.5m OSN 2.2m CAHA2.2m CAHA 4.2m WHT4.2m WHT 3.5m ARC3.5m ARC

(de Ugarte Postigo et al. 2006)



A different afterglowA different afterglow

No bright host galaxy.No bright host galaxy. Very red afterglow, (R-K)~4.5Very red afterglow, (R-K)~4.5

K R



GRB 060121: Spectral energyGRB 060121: Spectral energydistributiondistribution

UBVRIKUBVRIK SED SED Very sharp fluxVery sharp flux

break in V-band.break in V-band. Very high redshiftVery high redshift

(z=4.6) or lower(z=4.6) or lowerredshift withredshift withstrong extinction.strong extinction.



ModelisationModelisation of the light curve of the light curve

Fireball model.Fireball model. From optical to X-ray.From optical to X-ray. Two energy injectionsTwo energy injections

at 0.035 and 0.23 days.at 0.035 and 0.23 days. Better fit for highBetter fit for high

redshift.redshift.



The host galaxy of GRB 060121The host galaxy of GRB 060121

HST found a faint red galaxy of F606WHST found a faint red galaxy of F606WABAB~27.3 and~27.3 andF160WF160WABAB~24.5~24.5

The limited information is consistent with the SEDThe limited information is consistent with the SED

1’10”

2.2mCAHA+4.2m WHT2.5m HST

(Levan et al. 2006)



Redshift distributionRedshift distribution

Bayesian photo-redshift ofBayesian photo-redshift ofthe afterglow and the hostthe afterglow and the hostgalaxy (Benitez et al. 2004)galaxy (Benitez et al. 2004)

The combination of bothThe combination of bothfavours the high-z withfavours the high-z with70% probability70% probability

Extinction based prior as aExtinction based prior as asoft constrainsoft constrain

98% for high-z with prior98% for high-z with prior



Short burst?Short burst?

Duration Duration Short burst Short burst 68% probability of68% probability of

being an intermediatebeing an intermediate((HorváthHorváth et al. 1998) et al. 1998)

At z=4.6 it would moveAt z=4.6 it would moveto the centre of theto the centre of theshort burst distribution.short burst distribution.

Spectral lag (2Spectral lag (2-14-14+29 +29 ms)ms)

Soft tail (70-120 s)Soft tail (70-120 s)((DonaghyDonaghy et al. 2006) et al. 2006)



EnergeticsEnergetics of GRB 060121 of GRB 060121

z=4.6 z=4.6 ══▶▶ EEγγ,iso,iso=2.4×10=2.4×105353ergerg z=1.7 z=1.7 ══▶▶ EEγγ,iso,iso=3.7×10=3.7×105252ergerg Previous measures for short burstsPrevious measures for short bursts

10104848>>EEγγ,iso,iso>10>105151 erg erg Large conversion efficiency into neutrinoLarge conversion efficiency into neutrino

emission (emission (≥≥0.05), large accretion disk (0.05), large accretion disk (≥≥0.1M0.1Msolsol)) If energy extracted via If energy extracted via BlanfordBlanford--ZnajekZnajek processprocess

((BB-Z 1977), a-Z 1977), a>0.3, B >0.3, B ≥≥10101616G, MG, MBH BH ≥≥0.3M0.3Msolsol



ImplicationsImplications

There is an emerging population of short burstsThere is an emerging population of short burstsat high-z with energies comparable to longat high-z with energies comparable to longevents (events (EEγγ,iso,iso ~ 10 ~ 105252-10-105353 erg). erg).

This short bursts could be still generated byThis short bursts could be still generated bycompact mergers, but would need to push thecompact mergers, but would need to push thelimits of the models.limits of the models.

GRB 060121 would favour the models thatGRB 060121 would favour the models thatfollow the SFR with delays of 1 follow the SFR with delays of 1 GyrGyr from those from thoseof very old populations.of very old populations.



Further observationsFurther observationsof high-of high-zz short GRBs short GRBs

GRB 060313 showed a bright afterglow with aGRB 060313 showed a bright afterglow with avery faint host galaxy.very faint host galaxy.

E. Berger et al. (2006) have carried out a surveyE. Berger et al. (2006) have carried out a surveyof the error boxes of short GRBs searching forof the error boxes of short GRBs searching forhost galaxies:host galaxies: In 7 cases they find faint hosts (R~23-26.5) at zIn 7 cases they find faint hosts (R~23-26.5) at z≥≥11 1/4 1/4 –– 2/3 of short bursts originate at z > 0.7 2/3 of short bursts originate at z > 0.7 An additional photometric measure of the host ofAn additional photometric measure of the host of

GRB 060121 favours the high-z scenario.GRB 060121 favours the high-z scenario.



Hot news!Hot news!

Recent observations from HST complete theRecent observations from HST complete thehost SED in 6 bands (host SED in 6 bands (LevanLevan et al. in prep.) et al. in prep.)

The observation in F555W (555nm) shows noThe observation in F555W (555nm) shows nodetection in spite of deep exposure (9600s)detection in spite of deep exposure (9600s)

Very preliminary results show a possible fit at aVery preliminary results show a possible fit at aredshift of 4.2 (chiredshift of 4.2 (chi22/d.o.f.=4.2) and an/d.o.f.=4.2) and analternative case of 0.6 (chialternative case of 0.6 (chi22/d.o.f.=4.0)/d.o.f.=4.0)

Again Again favours the high z scenariofavours the high z scenario

ConclusionsConclusions

GRB 060121 could be the first of a new populationGRB 060121 could be the first of a new populationof short GRBsof short GRBs

There is a significant part of short GRBs happeningThere is a significant part of short GRBs happeningat high redshiftat high redshift

The range of energy release in short bursts is veryThe range of energy release in short bursts is verywide, both in prompt emission and afterglowwide, both in prompt emission and afterglow

The division could be due to several reasons:The division could be due to several reasons: NS-NS vs. NS-BHNS-NS vs. NS-BH Old vs. young mergersOld vs. young mergers Different environmentsDifferent environments



Future workFuture work

SpectroscopySpectroscopy: There is still no successful spectra: There is still no successful spectraobtained of the afterglow of a short GRBobtained of the afterglow of a short GRB

Early emissionEarly emission: Robotic telescopes have not yet: Robotic telescopes have not yetbeen able to record prompt emissionbeen able to record prompt emission

MultibandMultiband studies studies: Have proved useful to: Have proved useful toestimate redshift and learn about the environmentestimate redshift and learn about the environment

Gravitational wavesGravitational waves??

•Introduction•First SGRBs•GRB 060121•Further obs•Conclusions


Thanks!Thanks!

More information: de Ugarte Postigo et al. 2006, More information: de Ugarte Postigo et al. 2006, ApJApJ 648, L83 648, L83

grb 060121: implications of a short-burst at high redshift

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