Gamma-Ray BurstsGamma-Ray Bursts

Mano-a-ManoMano-a-Mano

Short bursts T<2sNS-NS/NS-BH??

GRB duration distribution

Lazzati and Perna

Long Burstsmassive stars

Mazets et al. 1981, Norris et al. 1984, Kouveliotou et al. 1993

Duration

100-300kev / 50-100keV Hardness ratio vs Duration

Collapsar model: LGRBs• explains naturally the association of some LGRBs

with supernove (Typ Ic), and their general emergence in star-forming regions.

• But the spectroscopically confirmed GRB/SN are quite different from normal LGRBs.– 4 out of the six events: LLGRBs– Eiso: 2-3 order mag smaller, softer spectrum, no

evidence of high energy tail– LLGRBs: light curve: smooth, only a single peak– Detected at low redshift z<0.1, – Event rate: 230Gpc^-3 yr^-1, 100-1000 times higher

than LGRB rate.

3

• GRB 030329: Optical afterglow

– spectral signature of type-Ic supernova

Stanek et al. 2003

GRB 060218-SN2006aj (d=145Mpc)

Ia

Ic

Ib

94I

97ef98bw

HeCaO

SiII

Hypernovae

Spectra of Supernovae & Hypernovae

Hypernovae (broad line type Ic)：

broad featuresblended linesLarge mass at high

velocities

H/no H

SN II SN I

Si/no Si

Ia He/no He

Ib Ic

6

Sazanov et al. 2004

Low Luminosity GRBs

Bromberg et al. 2011

7

No Direct Evidences so far:

(Until GW detection?)

• Host galaxies• Offset from host galaxy centers: kicks• Red shift distribution• Deep limits to supernova

Short GRBs and Compact stellar mergers

8

Long GRBs found exclusively in star-forming galaxies

Short GRBs found in both no star-forming and star-forming galaxies

afterglowGehrels et al. 2009

elliptical galaxies

z=0.26

9

• ~50% unclassified– due to their faintness, the absence of deep follow-up

• GRB 050724 in elliptical galaxy– GRB 050509b, GRB 050813– an older stellar population

• the others (the majority) in star-forming galaxies– LGRBs occurring in the brightest regions in host galaxies,

SGRBs environments under-represent the light distribution– distinct from LGRB hosts: SFRs, Luminosities, metallicities– higher L and metallicities: lower SFRs

23 Short bursts localized to better than a few arcsec

Berger 2009

Host galaxy classification/properties

10

Offset Distributionprojected offsets of bursts relative to host centers

median offset long bursts: ~1kpcshort bursts: ~5kpc

Fong et al. 2009

offset (kpc)0.1 1 10

no LGRBs: > 7kpcsome SGRBs: >15kpc

predicted distributions for NS-NSbased on pupulation synthesis models

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• Relatively high fraction at z<0.5, compared to long bursts– long-lived progenitors required

Redshift DistributionRedshift Distribution

Berger & Fong 2009

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τ ≥ 1Gyr

Ando 2004, Guetta&Piran 2005, Gal-Yam et al. 2005, Nakar et al. 2006, Zheng and Ramirez-Ruiz 2007, Berger 2007. however, Virgili et al. 2009, Lazzati et al. 2009

observed local ratesshort: ~10 /Gpc^3/yrlong: ~0.5/Gpc^3/yr

Nakar 2007

NS-NS: 1-800 /Gpc^3/yrNS-BH: 0.1-1000/Gpc^3/yr

median long:z~2.5short:z~0.25

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• Optical observation limits: – over 50 times fainter than normal Type Ic

– 5 times fainter than the faintest known Type Ic

A lack of an associated supernova with short bursts

Lee & Ramirez-Ruiz 2007

low redshift short bursts: GRB 050509B (z=0.225) GRB 050709 (0.16)

SN light curves as they would appear at z=0.225

energetic Type Icassociated with long GRB 980425

faint Type Ic

Hjorth et al. 2005, Fox et al. 2005, Castro-Tirado et al. 2005, Bloom et al. 2006

13

• GRB 060614: T90= 102sec– low redshift z=0.125, bright event– 100 times fainter than SN1998bw, fainter

than the faintest known Type Ic– collapsar-type event without supernova?

compact mergers with extended emission? something else?

Long bursts: without SN componentschallenge the usual classification of GRBs

GRB 060505, 060614

0 100sec50sec

~0.2sec hard pulse+soft emission

Gal-Yam et al. 2006, Fynbo et al. 2006, Norris&Bonnell 2006, Zhang et al. 2007, Lazzati et al. 2001

Other LGRBs at z<0.4 have had SN featuresGRB980425,031203,030329,011121

14

Li & Ramirez-Ruiz 2007Antonelli et al. 209

Isotropic gamma-ray energy and redshiftthe spread in energy due to the spread in opening angle or energy release?

long GRBs

short GRBs

090426z=2.6E=5x10^51erg

Collimationangles

16

Long bursts

Collimationcollapsar: the stellar evelope of the collapsing starmerger: wind from the surrounding accretion disk?

Burrows et al. 2006

beaming factor

€

long : fb-1 ≈ 75

short : 1 < fb-1 <100

Nakar 2007

EM counterpart• Mergers of DNS and NS-BH are likely to be

detected by adv LIGO/Virgo.

• The detection of EM counterpart– Independent of the discovery – Increasing the detector’s effective sensitivity

• Search restricted to nearby universe (a few hundred Mpc, z~0.1), but Error box: tens sq degree

17

Various EM counterparts• Short GRBs

– Birght, but rare within z~0.1– Expected rate < 0.03 SGRBs per year localized by Swift in

the rage, all-sky: 0.3 per yer• Orphan afterglows: relativistic jet, subrelativistic outflow

– Jets nearly pointing the Earth– Optical@day, LSST, a few per year– Radio (EVLA, LOFAR): uncertain peak time

• Macronova/kilonova: radioactive decay of heavy elements synthesized in the ejecta– If 0.01Msun ejected, optical emission at 300Mpc peaks after 1day at

mv~23mag.

18

Metzger&Berger; Nakar&Piran

€

θobs < 2θ j

LOS€

θ j

€

θobj

Subrelativistic outflows

• Numerical simulations: unbound tidal tail, winds driven by neutrino heating from proto-neutron star or AD– 10^50erg at (0.1-0.2)c : Robust prediction?

– discussion on synchrotron emission from blast wave is very similar to that for GRB afterglows

– Particle acceleration, B-fields: eps_e, eps_B, p20

Nakar&Piran

Outflow propagates at a constant velocityUntil it collects a mass comparable to its own.

€

If βi ≈1, tdec ≈ a few weeks after the mergers : typical freq ~ 1GHz

If βi = 0.1− 0.2, tdec ≈ years : typical freq < 150MHz€

tdec =Rdeccβi

≈ 30E491/ 3n0

−1/ 3βi−5 / 3 days

EVLA (1.4GHz) one-hour horizon: 1Gpc (beta=1) and 370Mpc (beta=0.2)LOFAR(150MHz) : 35Mpc and 90Mpc

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Fν ,peak ~ 0.3mJy ∝ EnεBε e