1. Hyperaccreting Disks around Neutrons Stars and Magnetars for GRBs: Neutrino Annihilation and Strong Magnetic Fields Dong Zhang (Ohio State) Zi-Gao Dai (Nanjing Univ)

2. 張 棟 尾張の大うつけ

3. Outline Why Neutron Star Disks? Differences between Neutron Star Disks and Black Hole Disks Effects of Strong Magnetic Fields from the Center Star (Magnetar)

4. Models of GRB inner engines (from Nakar’s PPT) LMXB NS-NS NS-BH WD - WD NS Quark star AIC Merger Accretion disk + Black whole msec magnetar >10 16 G magnetar Merger (AIC) Phase transition Quark star

5. Neutrino-cooled accretion disks High accretion rate ~0.01-10 Msun/s Short accreting timescale ~ 0.1-1s High density, temperature and pressure 10 9 - 10 11 g cm -3, 10 10 -10 11 K Optically thick Neutrino-cooled ~ 10 51 -10 53 erg/s electron-positron capture, electron- position pair annihilation, nucleon bremsstrahlung, plasmma decay Different types of flows ADAFs, CDAFs, NDAFs Ref. Eichler et al. 1989 Paczynski 1991 Narayan et al. 1992 Popham et al. 1999 Narayan et al. 2001 Kohri & Mineshige 2002 Di Matteo et al. 2002 Lee et al. 2005 Gu et al. 2006 Chen & Beloborodov 2007 Liu et al. 2007 Janiuk et al. 2007

6. Why Neutron Star Disks? A neutron star can survive after collapses and mergers X-ray flares after some GRBs may be due to a series of magnetic activities of pulsars (Dai et al. 2006 ). The GRBs themselves may originate from transient hyperaccreting disks surrounding neutron stars via neutrino or magnetic processes. Hyperaccreting disks could also provide the material and energy for SN associated with GRB. Magnetar (Thompson’s talk). We focus on the stellar- disk system.

7. Two region steady disk model Advection-dominated outer disk Self-similar inner disk NS Shock wave ??

8. NS vs BH ： Neutrino Luminosity Zhang & Dai (2008)

9. Neutrino Annihilation Zhang & Dai (2009a)

11. Relativistic Jet? More powerful neutrino annihilation rate along the disk polar region But heavier mass loss rate for ~ 100ms >100 ms: depending on the accretion rate and boundary condition

12. Dessart et al. 2009

13. Strong Magnetic Fields Lovelace et al. (1995)

14. Strong Magnetic Fields (>10^15 G) Microphysics Disk Dynamic Equations Angular Momentum Joule Heating Funnel Accretion

15. Magnetic Fields: Open Configuration Accretion Rate: 0.1 M_0/s Zhang & Dai (2009b)

16. Funnel Accretion Romanova (2007) Long (2008)

18. Energy from…

19. Summary Newborn neutron stars have been invoked to be central engines of GRBs in some origin/afterglow models. Hyperaccreting disks surrounding pulsars could provide an energy source for some explosions via neutrino/magnetic processes. Compared with the black-hole disk, the neutron star disk can cool more efficiently and produce a much higher neutrino luminosity. Some GRBs may originate from neutrino annihilation. The ultra-highly magnetic fields for magnetars could play a significant role to change the disk properties and produce a energetic relativisitic jet.

20. Thank You !