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

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

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

Properties of low-luminosity GRBs

• Low luminosity 1046-1048 erg/s (~10-4 than long GRBs) and low energy 1048 - 1050 erg

Swift GRBs

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

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)

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?

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

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.

tγ = te - tb

ttbb ttγγ

ttee

GRBduration

EngineWork time

Time for jetto break out

ttbb tt

tteeLess lik

ely

Less likely

The engine is unaware that the jet breaks out

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

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?

Relativistic shock breakout(EN & Sari 2012)

Energy releaseradiation-dominatedshock

Shock breakout“first light”

Continuous diffusion

Shock accelerates insteep density gradient

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

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

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)

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

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

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

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

Emission following the shock breakout

EN & Sari 12

-rays

X-rays

Ep shifts from -rays to X-rays (Ex > E)~

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

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

?

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

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

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

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)

Thanks

-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