gamma-ray bursts mano-a-mano
DESCRIPTION
Gamma-Ray Bursts Mano-a-Mano. GRB duration distribution. Long Bursts massive stars. Hardness ratio vs Duration. Short bursts TTRANSCRIPT
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.
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• 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
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Sazanov et al. 2004
Low Luminosity GRBs
Bromberg et al. 2011
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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
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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
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• ~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
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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
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• 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
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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
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Long bursts
Collimationcollapsar: the stellar evelope of the collapsing starmerger: wind from the surrounding accretion disk?
Burrows et al. 2006
beaming factor
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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
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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.
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Metzger&Berger; Nakar&Piran
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θobs < 2θ j
LOS€
θ j
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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.
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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