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Short GRBs -Short GRBs -and other recent and other recent

developments in GRBs developments in GRBs Tsvi PiranTsvi Piran ( (HU, Jerusalem)HU, Jerusalem)

Dafne GuettaDafne Guetta (Rome Obs.) (Rome Obs.)

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• 92 GRBs detected (~100 per 92 GRBs detected (~100 per year)year)

• 72 XRT detections out of 79 72 XRT detections out of 79 observedobserved

• 20 UVOT detections out of 20 UVOT detections out of 68 observed 68 observed

(42 detections ground-based (42 detections ground-based + UVOT)+ UVOT)

SwiftSwift

BAT UVOT XRT

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Short GRBs

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Understanding sGRBs

The key to answering these questions is precise positions enabled by the discovery of long-lived afterglows.

• How far away are they?Redshift distribution, rates

• How much energy do they release? Isotropic vs. collimated (opening angles)Lifetime of the central engineRadiative efficiency / afterglow energyNon-relativistic ejecta?

• In what type of environment are they located?host galaxies, offsetscircumburst density and profile

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Afterglows

Panaitescu et al. 2001

The afterglows are expected to be fainter as a result of a lower energy deposit (and possibly lower density if large kick)

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The Internal-External Fireball ModelThe Internal-External Fireball Model

InternalShocks

-rays

10101313-10-101515cmcm

ExternalShock

Afterglow

10101616-10-101818cmcm

Relativistic Outflow

InnerEngine

101066cmcm

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Short GRB Afterglow Searches

Hurley et al. 2002

Pre-Swift searches limited by large error boxes and delayed triggers

Optical Radio

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GRB 050509bGehrels et al. 2005

F = 9.5 10-9 erg/cm2

T90 = 40 msec

11 photons detected by XRT 9.3 radius (90%)

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GRB 050509bSwift/XRT position intersects a bright elliptical at z = 0.226 (but also

contains >10 higher redshift galaxies); No optical/radio afterglow

Bloom et al. 2005Castro-Tirado et al. 2005Gehrels et al. 2005Hjorth et al. 2005

IFIF elliptical host

Progenitors related to an old stellar

population

Kulkarni et al. 2005

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GRB 050509bKulkarni et al. 2005

=0.5

=0.05

Hjorth et al. 2005

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GRB 050709

Villasenor et al. 2005

Short-hard spike Soft bump (no oscillations)

Roughly equal energy in each component

Hjorth et al. 2005

Afterglow discovered with Chandra, followed up from ground and with HST; no radio

host is an irregular, star-forming galaxy at z = 0.16

Fox et al. 2005

z = 0.16

Was the progenitor a massive star?

Was 050509b a chance coincidence?

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GRB 050709

Parameters*:E ~ 51048 ergn ~ 0.01 cm-2

e ~ B ~ 1/3

Fox et al. 2005

Hjorth et al. 2005

Lack of SN detection supports a non-massive star origin

* but, lack of radio detection degenerate solutions

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GRB 050724Barthelmy al. 2005

250 ms

100 s

T90 = 31 s

15-25 keV

15-150 keV F610-7 erg/cm2 (short peak)

F710-7 erg/cm2 (soft tail)

flare 1

flare 2

flare 3

t-7

t-2.5

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GRB 050724Berger et al. 2005

• Radio/optical/NIR/X-ray afterglow

• z = 0.257

• jet with ~ 10o

• E1048 erg 100x lower than long GRBs

• Blastwave & engine physics are likely the same but with a lower E

Flare 3 also detected in the optical energy injection into the FS

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GRB 050724

Berger et al. 2005Prochaska et al. 2005

Definitive association with an elliptical galaxy*

Star formation rate at the position of the GRB is < 0.05 M/yr

old stellar population (no H >1 Gyr) NS-NS/NS-BH merger?

*The secure association lends support to the association of 050509b with an elliptical

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Gladders & Berger in prep.

z = 0.72

Magellan PANIC+LDSS3

GRB 050813

Gladders & Berger: a cluster at the position of the X-ray afterglow, z ~ 0.72 (Berger 2005; Prochaska et al. 2005)

F= 1.2410-7 erg/cm2

T90 = 0.6 s

z 1.8

Age < 3 Gyr

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Short GRB Summary

Conclusions:

• Short GRBs have >103 lower Eiso than long GRBs

• Association with low SFR hosts argues against collapsar origin

Name Redshift Afteglow Host Eiso(15-350keV) What might it be? (erg) .

SHB050202 ? no slew ?SHB050509B 0.225 XT Elliptical 1x1048 NS-NS mergerSHB050709* 0.161 XT, OT SF galaxy 6x1049 NS-NS mergerSHB050724 0.258 XT, OT, RT Elliptical 3x1050 NS-NS / NS-BH mergerSHB050813 0.722 XT ? (cluster) 2x1050 ? NS-NS merger

SHB050906 ? 0.03 ? ? galaxy ? ? minimal afterglow SSB050925 ? ? in gal. plane - ? possible new SGRSHB051105A ? ? - - ? minimal afterglow

* HETE

Ia:CC Ia:CC sGRB:lGRB sGRB:lGRB (Bloom)(Bloom)

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Pre-History Pre-History

TP 92 : TP 92 : Bursts from mergers lag after SFRBursts from mergers lag after SFR Mao, Narayan & TP 94:Mao, Narayan & TP 94: <V/V<V/Vmaxmax>>shortshort=0.4=0.4

Cohen & TP 95, TP 94: Cohen & TP 95, TP 94: ZZmaxmax shortshort 0.5 0.5

Katz & Canel 96: Katz & Canel 96: <V/V<V/Vmaxmax>>shortshort=0.4=0.4

ZZmaxmax shortshort 0.5 0.5

TheThe observed observed short bursts are significantly short bursts are significantly nearer than the nearer than the observedobserved long ones. long ones.

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Rates from Flux

N(>F) Number of N(>F) Number of bursts with flux >F bursts with flux >F

n(z) Rate as a function of zn(z) Rate as a function of z(L)(L)Luminosity functionLuminosity function{{

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0

),,(

0)()()(

max

LdLzndzFNpFLZ

Rates from Flux

Number of bursts with flux >FNumber of bursts with flux >F Rate as a function of zRate as a function of z Luminosity functionLuminosity function Maximal redshift for detection of a burst with a luminosity Maximal redshift for detection of a burst with a luminosity

L given the detector’s sensitivity p.L given the detector’s sensitivity p.

26Guetta & TP 05a,bGuetta & TP 05a,b

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Evidence for an Evidence for an old populationold population

From Nakar, Gal Yam & Fox 05From Nakar, Gal Yam & Fox 05

Kulkarni & Cameron

Red ellipticalz=0.258L=1.6 L*

SFR<0.03 M yr-1

Host of GRB 060724Keck/LGSAO/Narrow CameraK’ band

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Time lagTime lag

p(p() – ) – probability probability for a time for a time lag lag TP 92, TP 92, Ando 2004Ando 2004 dpztRzn

zt

SFR )(])([)()(

0

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Within the context of NS Within the context of NS mergers expect p(mergers expect p())1/1/ (TP 92)(TP 92)

-75 -50 -25 25 50 75 100

-75

-50

-25

25

50

75

111

)()(3

4

aada

ddaapdp

a

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Selection Selection effectseffects ??

ShortShort Too LongToo Long

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Comparison Comparison with Swift with Swift and HETE and HETE II short II short burstsbursts

??XX

??X?X?

XX

X?X?

XX

XXXX

32From Nakar, Gal Yam & Fox 05From Nakar, Gal Yam & Fox 05

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What did we learn from all that:What did we learn from all that:

2Gyr 3 with Mergers

Gyr 10 3 with Mergers

4

111023

cm

aGyr

-75 -50 -25 25 50 75 100

-75

-50

-25

25

50

75

35Two populations???Two populations???

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Correlation between sGRBs and Correlation between sGRBs and nearby IRAS Galaxies?nearby IRAS Galaxies?

Tanvir et al. 2005

5-25% @ z < 0.025

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Luminosity function and RatesLuminosity function and Rates

~10 /Gpc~10 /Gpc33/yr /yr 80 mergers 80 mergers /Myr Galaxy* /Myr Galaxy* *with beaming *with beaming

L*~2 10L*~2 105050erg/secerg/sec

Comparable to Comparable to the estimated the estimated rate of mergers rate of mergers (e.g (e.g Kalogera 04)Kalogera 04)

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Luminosity function and RatesLuminosity function and Rates

~104 /Gpc3/yr 8 104 mergers /Myr Galaxy

Nakar, Gal-Yam, Nakar, Gal-Yam, Fox 05,Fox 05,

L*~2 10L*~2 105050erg/secerg/secWeakly constrained Weakly constrained by current detectorsby current detectors

See also Tanvir 05See also Tanvir 05

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80 Myr/Galaxy 80 Myr/Galaxy 20 (0.5) events/yr within 200Mpc 1020 (0.5) events/yr within 200Mpc 105 5

Myr/Galaxy Myr/Galaxy 20 (1) events/yr within 40Mpc 20 (1) events/yr within 40Mpc

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SummarySummary Warning: these results are based on inverting Warning: these results are based on inverting

convolved triple integrals, small number statistics convolved triple integrals, small number statistics & selection effects.& selection effects.

Rate of short bursts >10 GpcRate of short bursts >10 Gpc-3-3yryr-1-1 with beaming with beaming this corresponds to the estimates of NS mergers. this corresponds to the estimates of NS mergers.

Time lag distribution requires a large fraction of Time lag distribution requires a large fraction of mergers with 3<mergers with 3<<10 Gyr – implications to <10 Gyr – implications to progenitorsprogenitors

The distribution of fluxes can be extrapolated to The distribution of fluxes can be extrapolated to significantly lower luminosities. These bursts are significantly lower luminosities. These bursts are weakly constrained by the current data. The event weakly constrained by the current data. The event rate may be as large as 10rate may be as large as 105 5 GpcGpc-3-3yryr-1-1

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The ENDThe END