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• Re’em Sari• Tsvi Piran
GRBs in the Era of Rapid Follow-upLiverpool, 2012
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Low-luminosity GRBs• ~10-4 lower luminosity, <1048 erg/s
• Much more frequent
• Smooth light curve
• E << total energy
• Not highly collimated
• Mildly relativistic ejecta with
energy ~ E
• Delayed X-ray emission, with
energy ~ E
• Not “successful” jets
Long
Short
Low luminosity
Wanderman & Piran 2011
• Low-luminosity GRB is NOT a regular GRB with low luminosity• Connection to long GRBs is mainly via the common association to broad-line Ic SNe
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Outline
• Propagation of a relativistic jet in a stellar envelope
• Why low-luminosity GRBs are not 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
• A note on short GRB classification
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Jet propagation in a stellar envelope
NumericalMacfadyan, Woosley, Zhang ,Morsony, Lazzati, Mizuta, Aloy, Nagakura, Tominaga, Nagataki, Ioka ...
AnalyticBegelman, Matzner, Meszaros, Waxman, Lazzati, Bromberg, ...
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JetMedium
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JetMedium
Head
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JetMedium
Cocoon
Head
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JetMedium
Cocoon
Head
Collimation Shock
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Morsony et al., 07
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• The head is slower than the jet material, and dissipates the jet energy.
• In order to propagate the head needs to be pushed by the jet material.
• The engine must work continuously until the jet breaks out.
To observe a long GRB: the jet must break out
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• The head is slower than the jet material, and dissipates the jet energy.
• In order to propagate the head needs to be pushed by the jet material.
• The engine must work continuously until the jet breaks out – or it will fail.
• Breakout time:
To observe a GRB: the jet must break out
Failed jet
313232
0
31
51 15510/10sec15
M
M
R
R
serg
Lt isob
ʘ ʘ
Bromberg, EN, Piran & Sari 11
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Are low-luminosity GRBs produced by “successful” jets?
(Bromberg, EN & Piran 2011)
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tγ = te - tb
ttbb ttγγ
ttee
After the jet breaks out energy flows (relatively) freely to large distances where the prompt GRB emission is emitted.
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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 2012
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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
What are the observed signatures of the resulting shock breakouts?
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Relativistic shock breakout(EN & Sari 2012)
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Shock breakout
Shock accelerates while its energy decreases
Shock width = distance to edge
Radiation dominated shock: =c/v
Shock breakout
radiation-dominatedshock
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Relativistic shock breakout
Main physical properties:
• Constant post shock rest frame temperature ~100-200 keV
• Temperature dependent (pair) opacity
• Significant post breakout acceleration 31 initialfinal
104
105
10-2
10-1
100
101
102
V (km/s)
T (
ke
V)
TBB
pairs
Katz et. al., 10Budnik et. al., 10
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Three observables depend on two physical parameters: R and
Relativistic breakout relationfor quasi-spherical breakout without wind
s22
sunbo
bobo R
Rt
keV 50 boboT
7.22/1
46 keV 50erg 10s 20
bobobo TEt
The breakout emission - A flash of -raysColgate was correct after all (for wrong reasons)
erg 102
2/3144
sun
bobobo R
RE
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s22
sunbo
bobo R
Rt
keV 50 boboT
The breakout emission - A flash of -raysColgate was correct after all (for wrong reasons)
erg 102
2/3144
sun
bobobo R
RE
Important note The photosphere is not in thermal equilibrium
The blackbody radius (Rbb2 = L/4T4) is meaningless
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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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Are low-luminosity GRBs produced by relativistic shock breakouts?
Colgate 1968, Kulkarni et al., 1998, Tan et al., 2001, Campana et al., 2006, Waxman et al., 2007, Wang et al., 2007, Katz et al., 2010
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Predictions of relativistic shock breakouts from “failed” jets and a comparison to low luminosity GRBs:
• Smooth light curve
• E << total energy
• Relativistic ejecta with energy ~ E
• Delayed X-ray emission, with energy ~ E(e.g., X-ray echo of GRB 031203)
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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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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-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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BATSE T90 (50 - 300 keV) Swift T90 (15 - 350 keV)
The threshold duration for Swift sample must be shorter than for BATSE sample !!!
We show that it is 0.6-0.7 s (Bromberg, EN, Piran & Sari 12)
A note on short GRB classification
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Summary• Relativistic breakouts produce -ray flares with characteristic properties:
• Ebo – Tbo – tbo relation (if quasi-spherical without wind)• smooth• a small fraction of total explosion energy• to X-ray evolution• generate a relativistic outflow with E~Ebo
• Low-luminosity GRBs, which are fundamentally different than long GRBs, show all these characteristics
• Failed jets is the most natural mechanism (explains also the high low luminosity GRB rate)
• Swift GRBs with 1s < T < 2s are most likely (>50%) collapsars
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Thanks
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t
25
12
6
3/115
3/211
3/2
1050
3/1
s 15
MRLt ob
L 51
Zhang et al., 04
Comparison with simulations
Bromberg, EN, Piran Sari 11
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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