Low-luminosity GRBs and Relativistic shock breakouts Ehud Nakar Tel Aviv University
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Low-luminosity GRBsand
Relativistic shock breakouts
Ehud Nakar Tel Aviv University
• Omer Bromberg• Tsvi Piran• Re’em Sari
2nd EUL Workshop on Gamma-Ray BurstsMoscow, 2013
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Outline
• Observational properties of Low-luminosity GRBs
• Why low-luminosity GRBs are unlikely to be generated by “successful” jets (as long GRBs)
• Theory of relativistic shock breakout (>0.5)
• Comparison of relativistic shock breakout predictions to low-luminosity GRB observations
• Shock breakout in regular long GRBs
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Low-luminosity GRBs
There are 4 low-luminosity GRBs observed to date with a confirmed associated SNe and known redshifts.
• Two with regular duration (~20 s) and two are very long (~2000 s)
• All are nearby, ~40-400 Mpc.
• All are associated with a very rare supernova type: Broad-line Ic SNe
• Nearby long GRBs are also associated with similar unique type of SNe
Low-luminosity GRB high energy emission is very different than that of long GRBs
The strong connection between the two types is based on the mutual association with Broad-line Ic SNe
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Properties of low-luminosity GRBs
• Low luminosity 1046-1048 erg/s (~10-4 than long GRBs) and low energy 1048 - 1050 erg
Swift GRBs
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Properties of low-luminosity GRBs
• Low luminosity 1046-1048 erg/s (~10-4 than long GRBs) and low energy 1048 - 1050 erg
•High volumetric rate (x1000 that of long GRBs). Not an extrapolation of long GRB rate to low luminosities
Long
Short
Low luminosity
Wanderman & Piran 2011
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Properties of low-luminosity GRBs
• Low luminosity 1046-1048 erg/s (~10-4 than long GRBs) and low energy 1048 - 1050 erg
•High volumetric rate (x100 that of long GRBs). Not an extrapolation of long GRB rate to low luminosities
• Smooth light curves (very rare among long GRBs)
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Properties of low-luminosity GRBs
• Low luminosity 1046-1048 erg/s (~10-4 than long GRBs) and low energy 1048 - 1050 erg
•High volumetric rate (x100 that of long GRBs). Not an extrapolation of long GRB rate to low luminosities
• Smooth light curves (very rare among long GRBs)
• E << total kinetic energy in the explosion (~1052 erg)
• The gamma-rays are not highly collimated
• Mildly relativistic ejecta with energy ~ E
• Delayed X-ray emission, with energy ~ E
Low-Luminosity GRBs are very different than long GRBs. But, can they be produced in the same way?
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Long GRBs are generated by relativistic jets that successfully “punch” through their progenitor envelopes
Can low-luminosity GRBs be produced by “successful” jets?
Zhang et al., 04
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Before the jet punches through the star its energy is dissipated into its envelope
After the jet breaks out energy flows (relatively) freely to large distances where the prompt GRB emission is emitted.
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tγ = te - tb
ttbb ttγγ
ttee
GRBduration
EngineWork time
Time for jetto break out
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ttbb tt
tteeLess lik
ely
Less likely
The engine is unaware that the jet breaks out
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0.01 0.1 1 10T90/tb
# of
bur
sts
Low-luminosity
Long GRBs
Low-luminosity GRBs are most likely (2) not produced by jets that successfully punches through their progenitor envelope
Bromberg, EN & Piran 2011
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If not a successful jet then what is the -ray source of low-luminosity GRBs?
Even “failed” jets drive shocks that breakout of the stellar surface!
“failed” jets are much more frequent than successful ones (Bromberg et al 12)
What are the observed signatures of the resulting shock breakouts?
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Relativistic shock breakout(EN & Sari 2012)
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Energy releaseradiation-dominatedshock
Shock breakout“first light”
Continuous diffusion
Shock accelerates insteep density gradient
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Shock breakout
log
log
E
A self-similar radiation dominated shock is accelerating through the envelope, -0.23 (Johnson & Mckee 1971, Tan et al 2001, Pan & Sari 2006)
log log
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Shock breakout
Shock width = distance to edge
A self-similar radiation dominated shock is accelerating through the envelope, -0.23 (Johnson & Mckee 1971, Tan et al 2001, Pan & Sari 2006)
log
log
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Colgate (1968): SNe shocks before breakout:1.very high Lorentz factor2.radiation dominated at
thermal equilibrium
Burst of -rays (in some SNe and other explosions)
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The temperature behind the shock
Constant (independent of sh ) post shock rest frame temperature ~100-200 keV
104
105
10-2
10-1
100
101
102
V (km/s)
T (
keV
)
TBB
pairs
Katz et. al., 10Budnik et. al., 10
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The Observed temperature
• Following breakout the expanding gas accelerates up to
• The gas is loaded with pairs, trapping the radiation
• The trapped radiation can be released only when pairs annihilate at T`≈50 keV
)30(for 31 finalinitialfinal
keV 50 boboT
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Observed energy
The breakout energy is released from a region with Thomson optical depth ~ 1 (without pairs)
sun
2
10 M 102
sun
bobo R
Rm
erg 104
2
2/31442/31
2
sun
bobo
bobobo R
RcmE
Observed duration
Light travel time dominates the breakout duration
s22
sunbo
bobo R
Rt
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erg 102
2/3144
sun
bobobo R
RE
s22
sunbo
bobo R
Rt
keV 50 boboT
Three observables depend on two physical parameters
Relativistic breakout relation
7.22/1
46 keV 50erg 10s 20
bobobo TEt
The Observed signature of a relativistic breakout
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Emission following the shock breakout
EN & Sari 12
-rays
X-rays
Ep shifts from -rays to X-rays (Ex > E)~
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Which explosions are expected to have relativistic breakouts?
EN & Sari 11
95.0
*
2.1
sun
7.1
53
exp
5M5erg 10 14
sun
ejectalosionbo R
RME
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Other Predictions of relativistic shock breakouts:
• Smooth light curve
• E << total energy
• Relativistic ejecta with energy ~ E
• Delayed X-ray emission, with energy ~ E
• If the breakout is due to failed jets than rate >> than long GRBs
Relativistic breakout relation
7.22/1
46 keV 50erg 10 s 20
bobo
bo
TEt
?
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Low luminosity GRBs
GRB Ebo
(erg)Tbo
(keV)tbo
(s)Relation
tbo (s)Rbo
(cm)bo
980425 1048 150 30 10 61012 3
031203 5104
9
>200 30 <35 21013 >4
060218 5104
9
40 2100 1500 51013 1
100316D 5104
9
40 1300 1500 51013 1
Relativistic breakout relation
7.22/1
46 keV 50erg 10s 20
bobobo TEt
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A Wolf-Rayet with a radius of a red supergiant?
• Only a mass of 10-4 Mʘ is needed at this radius to produce the observed shock breakout
• Recent early time SNe light curves indicates on a compact massive mantle and a low mass extended envelope
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Shock breakout from long GRBs
s~ mtbo
MeV boT
erg 5
10~2
48
sun
bobo R
RE
A short, hard and faint pulse at the beginning of the burst
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Summary
• Low-luminosity GRBs are fundamentally different than long GRBs
• Relativistic breakouts produce -ray flares with characteristic properties:
• Ebo – Tbo – tbo relation (if quasi-spherical without a wind)• smooth• a small fraction of total explosion energy• to X-ray evolution• generate a relativistic outflow with E~Ebo
• Low-luminosity GRBs show all these characteristics
• Failed jets is the most natural mechanism (explains also the high low luminosity GRB rate)
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Thanks
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-ray flares from relativistic shock breakouts are expected in a range of other explosions. For example,
White dwarf explosions (Type Ia and .Ia SNe and AIC):
erg 1010~ 4240 boE
ms 301~ bot
MeV ~boT
Extremely energetic and compact supernovae (e.g., SN 2002ap):
erg 1010~ 4644 boE
s 303~ bot
keV 100~boT
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