The Progenitors of Short-Hard GRBsfrom an Extended Sample of Events

Avishay Gal-Yam Hubble Fellow

CALTECH

Outline

- Observational breakthrough 2005- An extended sample from the IPN- Population analysis – hosts- Final remarks

Short GRBs (SHBs) - Papers:

Nakar, Gal-Yam, Piran & Fox 2005, ApJ Fox et al. 2005, ApJL, 050509b

Fox et al. 2005, Nature, Oct. 6, 050709Berger et al. 2005, Nature, Nov. issue,

050724Gal-Yam et al. 2006, ApJ, Submitted, astro-ph/0509891

Nakar et al. 2006, ApJ, in press, astro-ph/0511254

Also:Bloom et al. 2005

Prochaska et al. 2005Tanvir et al. 2005

…

People:

E. Nakar (Caltech)

T. Piran (HUJI), D. Fox (Penn State), E. Ofek (Caltech)

(Extended) Caltech GRB group (Kulkarni, Frail, Berger, Cenko…)

The new SHB (Swift-HETE-Bursts) era

• Arcmin -> arcsec localizations -> hosts• 4 relevant bursts, as of August 2005

GRB 050509B: Swift Detection

Very faint GRB

X-ray: T+62 s detects 11 photons)!(

No optical, no radio. Very faint limits.

Giant elliptical galaxy in a cluster. z=0.22 . Host?

No SN

Geh

rels

et a

l. 20

05

T90=40 ms

HST Imaging: No Supernova

Fox et al. 2006 Error radius = 9.3 arcsec 4 HST EpochsMay 14 to June 10

48 sources in XRT error circle

Giant elliptical (Bloom et al 2005)L=1.5L*

SFR<0.1 M yr-1

SHB 050709: HETE Detection

A Hard spike, 84 keV

A Soft bump Roughly equal energy in each component

Vil

lase

nor

et a

l. 20

05

T90=70 ms

SHB 050709 - localization

• X-ray afterglow• Optical afterglow• Secure association

with a galaxy: late-type, z=0.16, moderate SFR (MW), lots of old stars (>1 GY) - Covino et al. 2005

• No SN

GRB 050724: Swift Detection

Hard spike/soft bump

X-ray, optical, IR and radio afterglow detected

Secure association with elliptical galaxy, z=0.26

No SN (Berger et al. 2006)

T90=40 ms

15-150 keV

15-25 keV

T90=3 s250 ms

100 sGal-Yam et al. 2005

SHB 050813: Swift Detection

• Another Swift SHB• Deep imaging identifies a high-z cluster (Gladders et al.

2006)• Initial spectroscopy shows z=0.722 (Berger 2005,

Prochaska et al. 2005) (but perhaps revised higher, z=1.8)

Recent Swift/HETE sample:

• Low redshift• Most in early types• No SNeSo:• Different from long GRBs• Similar to SNe Ia• Long lived progenitors• “A merger origin”?

Extended Sample from IPN

• Goal: Search for luminosity over-density inside or around old, small, IPN error boxes (either single luminous galaxies or galaxy overdensities - clusters)

• Sample: 4 small error boxes • Method: multicolor imaging (P60,

LCO100), spectoscopy (P200)• Comparison with SDSS luminosity

functions and galaxy densities.

SHB 790613• Smallest IPN box (<1

arcmin2)• 4 reddish galaxies with

similar colors – very high density (~1% prob.)

• 6.5’ away from Abell 1892 (z=0.09), <1% chance association in our entire sample

• Therefore assume: z=0.09 (nearest SHB), host likely early type, in cluster

26 years … !

SHB 000607• Small IPN box (5.6

arcmin2)• A single luminous

galaxy (R=17.57)• Sb galaxy at z=0.14,

~1.4 L* in SDSS r,i• Chance association 2%

for this error box, 7% for entire sample

• Therefore assume: z=0.14, intermediate spiral host

SHBs 001204, 021201• SHB 001204: Small IPN

box (6 arcmin2)• Several galaxies• Inconsistent redshifts

(0.31, 0.39), insignificant overdensity

• z>0.25 (1)

• SHB 021201: insignificant overdensity

• z>0.25 (1)

Z=0.31

Extended SHB sampleSHBHostRedshift

050509bE0.22050709Sbc/Sc0.16050724E0.26050813E/S0=>0.72790613E/S00.09000607Sb0.14001204>0.25021201>0.25

Comparison with SNe Ia

• SNe Ia occur in galaxies of all types

• But most of them occur in late-type galaxies !

• The normalized SN rate in Irr galaxies is 20 times that in E galaxies

• Comparison of the observed relative rates disfavors an identical distribution (P=7%)

• It appears like SHBs come from older progenitors (several Gy) (also: Zheng & Ramirez-Ruiz 2006)

Mannucci et al. 2005

Gal-Yam et al. 2006

Do we rule out NS-NS mergers?

• No.• Main limit is small numbers (both

SHBs and observed NS-NS pairs)• But, you really need to stretch to

fit the data• Observations disfavor DNS models• This is not changed by 050813

z>0.72 and 051221 (Soderberg et al. 2006)

Belczynski et al. 2006

E

Soderberg et al. 2006

Concluding remarks • Similar results from redshift distribution

(Nakar, Gal-Yam & Fox 2006)• Recent SHBs useless for similar analysis

due to sample incompleteness (~1/10 with data) and obvious strong selection effects (in favor of gas-rich systems)

• Additional observational effort imperative for further progress

• Possible high local rates of SHBs (See Nakar, Gal-Yam & Fox) mean the LIGO (I or II) may provide conclusive evidence for compact binary models

Thanks

The rate and progenitor lifetime of SHBs(Nakar, Gal-yam & Fox 2005)

Goals:•Using the extended sample to constrain the local rate and the progenitors lifetime of short GRBs. •Evaluate the compatibility of these results with the compact binary progenitor model.•Explore the implications for gravitational wave detection of these events with LIGO.

Method:

Comparing the observed redshift and luminosity distributions to predictions of various models of intrinsic redshift and luminosity distributions.

(this method is an extension of a method used by Piran 1992; Ando 2004; Guetta & Piran 2005,2006)

Cosmology+

Detector

~400 BATSE bursts with unknown z

Several bursts with known z

Consistency test

Intrinsic Observed

Redshift distribution

Luminosity function

Intrinsic Observed

Cosmology

Detector

If (L) is a single power-law:

In the case of BATSE SHBS a single power-law fits the data very well: (L) L-2±0.1

Porciani & Madau 2001

Star formation rateProgenitor lifetime distribution

+ =

Intrinsic redshift distribution

Results

typical > 4[1]Gyr (95% [99.9%] c.l.)

or if f() then > -0.5[-1] (95% [99.5%] c.l.)

*Similar results are obtained when we take z050813>0.72 **Similar results are obtained by Guetta & Piran 2006

Progenitor lifetime

Main uncertainties and limitations

•Luminosity function – any “knee” shaped broken power-law results in similar constraints. A short lifetime may be consistent with an “ankle” shaped broken power-law (expected in case of two populations of SHBs).

•Star-Formation History – the results are valid for any of the three Porciani & Madau (2001) SFH functions (all peak at z≈1.5).

•Detector Thresholds – important only if the luminosity function is not a single power-law (only Swift SHbs can be used). The results are valid for a range of reasonable threshold functions of Swift.

•Small sample – the results are only at a level of ~3and might be affected by unaccounted selection effects or wrong measurements.

Observed Local Rate(and robust lower limit)

-13, yr Gpc 10 obsSHB

-BATSE observed rate was 170 yr-1 -At least ¼ of these bursts are at D < 1Gpc

Similar result is obtained by Guetta & Piran 2006

Total Local rate

1-3

1

49min yr Gpc

erg/sec 1040

LfbSHB

We consdider here (L) L-2 with a lower cutoff Lmin

fb – beaming correction (30-50 Fox et al. 2005 ???)

Lmin – The current observation are insensitive to Lmin < 1049 erg/sec. Evidence for population of SHBs within ~100Mpc (Tanvir et al. 2005) suggests Lmin < 1047 erg/sec

Local rate – upper limit

SHB progenitors are (almost certainly) the end products of core-collapse supernovae (SNe).

The rate of core-collapse SNe at z~0.7 is 5×105 Gpc-3 yr-1 (Dahlen et al. 2004), therefore:

-135 yr Gpc 105 SHB

Observed NS-NS systems in our galaxy

Based on three systems, Kalogera et al. (2004) find:

(95%) yr 109.2107.1 -145

NSNS in our galaxy

And when extrapolating to the local universe:

yrGpc 3000200 -1-3 NSNS

This rate is dominated by the NS-NS system with the shortest lifetime – ~100 Myr (the double pulsar PSR J0737-3039). Excluding this system the rate is lower by a factor 6-7 (Kalogera et al. 2004).

SHBs and NS-NS mergers

For the two to be compatible there should be a hidden population of old long-lived NS-NS systems.

Can it be a result of selection effects?

Maybe, but we cannot think of an obvious one.

Caveat: small number statistics

NS-NS (Kalogera et al. 2004): 200<RNS-NS< 3000 Gpc-3 yr-1

Dominated by binaries that merge within ~100 Myr

SHBs (Nakar et al. 2005): 10<RSHB< 5·105 Gpc-3 yr-1

Dominated by old progenitors >4 Gyr

Detection of SHB increases LIGO range by a factor of 1.5-2.5 (Kochanek & Piran 1993):

•Timing information (~1.5) •Beaming perpendicular to the orbital plane (~1.5)•Localization information

LIGO-I: Probability for simultaneous detection

Swift detects and localizes ~10 SHBs yr-1. If Lmin~1047 erg/s and (L)L-2 then ~3% of these SHBs are at D<100 Mpc and ~1% at D<50 Mpc

R(merger+SHB) ~ 0.1 yr-1

Notes:•This result depends weakly on beaming•In this scenario RSHB ~ 1000 fb Gpc-3yr-1

•Comparison with Swift and IPN non-localized bursts may significantly increase this rate

Thanks!

Single power-law fit to (L)

Maximum likelihood: (L) L-2±0.1 2/d.o.f 1 a good fit

The extended sample (8 SHB) can be used

Tanvir et al. 2005

Long GRBs

SHBs

SHBs (E-Sbc galaxies)

SHBs Galaxies at D<100Mpc

At least 5% of BATSESHBs are at D<100Mpc

Our model predicts that 3% of the SHBs are at

D<100Mpc if Lmin 1047 erg/s

Broken power-law fit to (L)

Only Swift bursts can be used (unknown detector response for the rest). However we can carry a comparison with the two-dimensional L-z distribution

21

*

*

LL

LL )(

2

1

L

LL

For each f(), 1 and 2 we fit L* to BATSE dN/dP

typical > 3Gyr

or

>-0.5

Probability for blind search detection

LIGO-I: Taking a speculative but reasonable SHB rate of 104 Gpc-3 yr-1 predicts a detection rate of:

R(NS-NS) ~ 0.3 yr-1

R(BH*-NS) ~ 3 yr-1

*MBH ~ 10M

LIGO-II: The SHB rate lower limit of 10 Gpc-3 yr-1 implies:

R(NS-NS) ≥ 1 yr-1

R(BH*-NS) ≥ 10 yr-1

GRB missions

MissionOperationalSHB rate (yr-1)

localizednon-localized

Swift2005-2007+~10?

HETE-22001-2005+~1-

IPNyes~1~10*

GLAST2007-~30*-

*my rough estimate

LIGO-II: Probability for simultaneous detection

•This year 3 bursts detected at D < 1Gpc •GLAST is expected to detect several SHBs at D<500Mpc every year•LIGO-II range for simultaneous detection is ~700 Mpc (NS-NS) and ~1.3 Gpc (BH-NS)

Simultaneous operation of LIGO-II and an efficient SHB detector could yield at least several simultaneous detections each year.

Non-detection will exclude the compact merger progenitor model

Offset

39 ± 13 kpc 3.5 ± 1.3 kpc 2.4 ± 0.9 kpc

Prochaska et al., 2005