GRB efficiency Revisited & GRB efficiency Revisited & Magnetar behind short GRBMagnetar behind short GRB

Yizhong Fan(Racah Inst. Of Physics, Hebrew University of Jerusalem, Israel;

Purple Mountain Observatory, China)

CollaboratorsCollaborators

T. Piran (Hebrew University of Jerusalem, Israel)D. Xu (University of Copenhagen, Denmark)

Fan & Piran. 2006, MNRAS, 369, 197 Fan & Xu. 2006, MNRAS, submitted (astro-ph/0605445)

GRB efficiency crisis?GRB efficiency crisis?

GRB efficiency is defined as

Schematic features seen in early X-ray AfterglowSchematic features seen in early X-ray Afterglow(Zhang et al. 2006; Nousek et al. 2006)(Zhang et al. 2006; Nousek et al. 2006)

5.0~

5.0~

Pre-Swift GRBsPre-Swift GRBs

5.0~GRB efficiencyGRB efficiency crisis! crisis!

Late internal shocks Late internal shocks (Fan & Wei 2005; (Fan & Wei 2005;

Burrows et al. Burrows et al. 2005) ?2005) ?

Energy injection

To constrain with the late X-ray data

When the X-ray band is above the cooling frequency, the flux is only sensitively dependent on and (Kumar 2000; Freedman & Waxman 2001).

Fan & Piran 2006Fan & Piran 2006

Lloy-Ronning & Zhang 2004:

Fan & Piran 2006:

Causes: In Lloy-Ronning & Zhang (2004): 1. is too large to match the result of numerical calculation . 2. The inverse Compton effect has been ignored.

Our result:

The optical/X-ray afterglows of GRB 050401

De Pasquale et al. 2006 Rykoff et al. 2005

Energy injection, as many authors suggested? No! (Fan & Piran 2006)

8t

63.0t

41.1t

76.0t

9.0

66.0/

8.1,},max{

tdtdE

p

inj

Xmc 8.2, pcXm

1t

9.0, tFmR

63.0, tFRm

41.1t

5.0/ tdtdEinj

A possible solution for GRB 060401 ( ):

But: What’s the underlying physics?

The simple energy injection model has been challenged The simple energy injection model has been challenged by more and more data (Panaitescu et al. 2006)!by more and more data (Panaitescu et al. 2006)!

Is there a GRB efficiency crisis ?

The previous estimate on the GRB efficiency

(with the late afterglow data) is overestimated.

The energy injection model is not supported by

the optical data.

Magnetar behind short GRB?Magnetar behind short GRB?

What’s formed in the double neutron What’s formed in the double neutron star merger (theoretical star merger (theoretical

speculation)?speculation)?

Black hole (Eichler et al. 1989; Narayan et al. 1992)?

Differentially rotating normal neutron star (Kluzniak & Ruderman 1998; Dai et al. 2006)?

Magnetar (Rosswog et al. 2003; Gao & Fan 2006 ; Price & Rosswog 2006)?

Temporary magnetar (Shibata et al. 2006) ?

MHD Simulation

(Soderberg et al. 2006) (Soderberg et al. 2006)

stc 3000~st f 15000~

Energy injection ?

.3000~

,103~~

,~/

,15000~~

,/)1(~/108.2

51

0

44

616,

214,

48

st

ergEE

severalEE

stT

tEzRBserg

c

k

kinj

f

cks

sRIBT

Tz

tRB

z

serg

dt

dE

s

s

66,45

24

214,

40

2

0

44

66,

214,

48

106.1

])1(

1[1

/106.2

Energy injection form:Energy injection form:

Constraint on the parameters:Constraint on the parameters:

A millisecond pulsar with dipole magnetic A millisecond pulsar with dipole magnetic field Gauss is consistent with the data!field Gauss is consistent with the data!

sRIBT

Tz

tRB

z

serg

dt

dE

s

sinj

66,45

24

214,

40

2

0

44

66,

214,

48

106.1

])1(

1[1

/106.2

Fan & Xu (astro-ph/0605445)Fan & Xu (astro-ph/0605445)

With an energy With an energy injection from a injection from a

magnetarmagnetarWithout Without energy energy

injectioninjection

Conclusion: The central engine of short

GRB 051221A may be a millisecond magnetar.

Speculation:

A very late/weak

re-brightening.

Thank you!