1. GRB efficiency Revisited & Magnetar behind short GRB
Yizhong Fan
(Racah Inst. Of Physics, Hebrew University of Jerusalem, Israel;
Purple Mountain Observatory, China)

2. Collaborators 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/ )

3. GRB efficiency crisis?
GRB efficiency is defined as

4. Late internal shocks (Fan & Wei 2005;
Schematic features seen in early X-ray Afterglow (Zhang et al. 2006; Nousek et al. 2006)
Late internal shocks (Fan & Wei 2005;
Burrows et al. 2005) ?
Pre-Swift GRBs
GRB efficiency crisis!
Energy
injection

5. 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).

6. Fan & Piran 2006

7. Our result: Lloy-Ronning & Zhang 2004: Fan & Piran 2006:
Causes: In Lloy-Ronning & Zhang (2004):
is too large to match the result of numerical calculation .
2. The inverse Compton effect has been ignored.
Our result:

8. No! (Fan & Piran 2006) The optical/X-ray afterglows of GRB 050401
De Pasquale et al Rykoff et al. 2005
Energy injection, as many authors suggested?
No! (Fan & Piran 2006)

9. A possible solution for GRB 060401 ( ):
But: What’s the underlying physics?

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

11. 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.

12. Magnetar behind short GRB?

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

14. Energy injection ?
(Soderberg et al. 2006)

15. Energy injection form: Constraint on the parameters:
A millisecond pulsar with dipole magnetic field Gauss is consistent with the data!

16. With an energy injection from a magnetar Without energy injection
Fan & Xu (astro-ph/ )

17. A very late/weak re-brightening.
Conclusion: The central engine of short
GRB A may be a millisecond magnetar.
Speculation:
A very late/weak re-brightening.

18. Thank you!