1. Short-Duration Gamma-Ray Burst Central Engines
Brian Metzger Princeton University
In collaboration with
Eliot Quataert (Berkeley)
Todd Thompson (Ohio State)
Tony Piro (Berkeley)
Niccolo Bucciantini (Nordita)
Almudena Arcones (MPIK)
Gabriel Martinez-Pinedo (MPIK)
Title, swift has shown distinct populations, most popular model is NS mergers, crucial for ligo, swift has also confused the issue
Chandra / Einstein Fellows Symposium Harvard CfA, October

2. Gamma-Ray Bursts: Long & Short Duration
BATSE GRBs
Nakar 07

3. Gamma-Ray Bursts: Long & Short Duration
BATSE GRBs
Long
High Redshift, zavg ~ 2
Large Energies (Eiso~ ergs)
Star-Forming Host Galaxies
Type Ic Broad-Line Supernovae
Nakar 07

4. Gamma-Ray Bursts: Long & Short Duration
BATSE GRBs
Long
High Redshift, zavg ~ 2
Large Energies (Eiso~ ergs)
Star-Forming Host Galaxies
Type Ic Broad-Line Supernovae
Nakar 07
Nakar 07
Short

5. Merging Compact Objects (NS-NS or BH-NS) Paczynski 1986; Goodman 1986; Eichler+1989; Narayan+ 1992, …
t = 0.7 ms
Inspiral “Chirp” Gravitational Waves
t = 3 ms
Shibata & Taniguchi 2006
Target for Advanced LIGO
Disk left behind w/ mass ~ M & size ~ km
 cooling via neutrinos: ( >>1,  ~ 1 )

6. Accretion-Induced Collapse (AIC)
Binary Accretion or WD-WD Merger
“Failed” Type Ia SN
Collapse of rapidly-rotating WD  Disk around PNS: Mdisk ~ M
Circinus X-1 (Chandra)
Neutron Star Circinus X  > 15 ! (Fender et al. 2004)

7. Similar Systems - Distinct Origins
NS-NS / BH-NS Mergers BH
M ~ M R ~ 100 km
Accretion-Induced Collapse NS
consistent with short GRB durations

8. Short GRB Host Galaxies
GRB050509b
GRB050709
z = SFR = 0.2 M yr-1
Bloom+ 06
z = SFR < 0.1 M yr-1
KECK Bloom+06
HUBBLE Fox+05
GRB050724
Berger +05
z = SFR < 0.03 M yr-1
Berger+05

9. Short GRB Host Galaxies
GRB050509b
GRB050709
z = SFR = 0.2 M yr-1
Bloom +06
No Supernova!
z = SFR < 0.1 M yr-1
KECK Bloom+06
HUBBLE Fox+05
Lower redshift* (z ~ 0.1-1)
Eiso~ ergs*
Older Progenitor Population (Consistent with being drawn from field galaxies; Berger 09)
GRB050724
Berger +05
GRB050724
z = SFR < 0.03 M yr-1
Berger+05

10. Short GRBs with Extended X-Ray Emission
~25% of Swift Bursts (2 classes?) Similarity To GRB  Ongoing Engine Activity EEE/EGRB ~ 1-30 !
GRB050709
GRB080503
SEE/SGRB ~ 30
Perley et al. 2008
BATSE Examples (Norris & Bonnell 2006)

11. Evolution of the Remnant Disk
Metzger, Piro, Quataert 2008, 2009 (see also Beloborodov 2009; Lee et al. 2009)
Local Disk Mass r2 (M)
1-D Time-Dependent Models ( viscosity; realistic -cooling)

12. Powerful Winds Blow Apart Disk
Late-Time Outflows
Metzger et al. 2008, 2009
At t ~ seconds: R ~ 500 km, M ~ 0.3 Minitial, T ~ 1 MeV }
-Particle Formation
Thick Disks Marginally Bound
(Narayan & Yi 94; Blandford & Begelman 99)
EBIND ~ GMBHmn/2R ~ 3 MeV nucleon-1
Powerful Winds Blow Apart Disk 
ENUC ~ 7 MeV nucleon-1 BH
~20-40% of the Initial Disk is Ejected Back into Space!

13. ???

14. Tidal Tails in NS-NS/NS-BH Mergers
Lee & Ramirez-Ruiz 07
Tail(s) with ~10% prompt disk mass

15. Late-Time Fall-Back Accretion+
(Rosswog 07; Faber+06; Lee+09) a
Rosswog 07

16. r - Process Heating (not included in present simulations!)
Decompressing NS Matter  A ~ 100 Nuclei + Free Neutrons (Lattimer+77; Meyer 89):
Protons
Neutrons
Er ~ 1-3 MeV nucleon-1 released over theat ~ 1 second

17. + r-Process Network Calculations a
Metzger, Arcones, Quataert, Martinez-Pinedo 2009 a

18. Total r-Process Heating Along Fall-Back Orbits
Orbital Period
Binding Energy of Merger Ejecta

19. theat > 1 s
theat < 1 s + + a a
torb ~ 1 s

20. theat > 1 s
theat < 1 s + + a a
torb ~ 1 s
No Late Fall-Back

21. + + theat > 1 s theat < 1 s a a torb ~ 1 s “Gap”
No Late Fall-Back

22. The Effects of r-Process Heating on Fall-back Accretion
Metzger, Arcones, Quataert, Martinez-Pinedo 2009
Either: Complete Suppression of Fall-Back after t ~ 1 sec
OR “Gap” of t ~ seconds opened

23. ???

24. NS Magnetar Spin-Down  Accretion-Induced Collapse Following:
NS-NS Merger with long-lived NS remnant NS

25. Metzger, Quataert & Thompson 08
Magnetar Spin-Down
Following: 
Accretion-Induced Collapse
NS-NS Merger with long-lived NS remnant NS
High 
Low 
Internal Shock Emission
Power (1051 ergs s-1)
P0= 1 ms
1016 G
GRB Overlaid G
Metzger, Quataert & Thompson 08
 ~ 
1015 G

26. Conclusions Swift Revolution: Afterglows and Host Galaxies
 long and short GRBs have distinct progenitors
NS-NS/NS-BH Remains Promising Model
 consistent w/ host galaxies, durations, energetics
accretion disk spreads, explodes at t ~ 1 second.
 ~100 second X-ray Emission = Major Problem
Oft-Discussed Explanation = Fall-Back Accretion
r-process heating must be taken into account
 either: “natural” explanation or makes matters worse
AIC = Promising Alternative Model (NS Remains!)