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

Hyperaccreting Disks around
Neutrons Stars and Magnetars for
GRBs:
Neutrino Annihilation and Strong
Magnetic Fields
Dong Zhang (Ohio State)
Zi-Gao Dai (Nanjing Univ)
張
尾張の大うつけ
棟
Outline
• Why Neutron Star Disks?
• Differences between Neutron Star Disks
and Black Hole Disks
• Effects of Strong Magnetic Fields from the
Center Star (Magnetar)
Models of GRB inner engines
(from Nakar’s PPT)
LMXB
AIC
NS-NS
NS-BH
WD - WD
Merger
Merger
(AIC)
Accretion disk +
Black whole
msec
magnetar
>1016 G
magnetar
NS
Quark star
Phase
transition
Quark star
Neutrino-cooled accretion disks
• High accretion rate ~0.01-10
Msun/s
• Short accreting timescale
~ 0.1-1s
• High density, temperature
and pressure
109- 1011 g cm-3 , 1010 -1011K
• Optically thick
• Neutrino-cooled
~1051 -1053erg/s
electron-positron capture, electronposition 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
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 stellardisk system.
Two region steady disk model
Advection-dominated outer disk
Self-similar inner disk
NS
Shock wave ??
NS vs BH：Neutrino Luminosity
Zhang & Dai (2008)
Neutrino Annihilation
Zhang & Dai (2009a)
Zhang & Dai (2009a)
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
Dessart et al. 2009
Strong Magnetic Fields
Lovelace et al. (1995)
Strong Magnetic Fields (>10^15 G)
• Microphysics
• Disk Dynamic Equations
Angular Momentum
Joule Heating
• Funnel Accretion
Magnetic
Fields:
Open
Configuration
Accretion
Rate:
0.1 M_0/s
Zhang & Dai (2009b)
Funnel Accretion
Romanova (2007)
Long (2008)
Energy from…
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.
Thank You !