Optical Counterparts of Neutron Star Mergers
Powered by the Decay of R-Process Nuclei
Brian Metzger
Princeton University
NASA Einstein Fellow
In Collaboration with
Eliot Quataert, Siva Darbha, & Daniel Perley (UC Berkeley)
Almudena Arcones & Gabriel Martinez-Pinedo (GSI; Darmstadt, Germany)
Dan Kasen (UCSC), Roland Thomas & Peter Nugent (LBNL)
Binary Compact Object Mergers
NS
NS
BH
NS
10 Known Galactic NS-NS Binaries
(Lorimer 2008)
Hulse-Taylor
Pulsar
Tmerge = 300 Myr
-5
-4
-1
˙
N
~
10
-10
yr
merge
(e.g. Kalogera et al. 2004)
Gravitational Waves from Inspiral and
Merger
Credit: Kip Thorne
“chirp
”
Ground-Based
Interferometers
LIGO 5th Science Run
(2007) Range ~ 10-30 Mpc
“Advanced” LIGO+Virgo
(~2015) Range ~ 300-600 Mpc
LIGO (North America)
Virgo (Europe)
Electromagnetic Counterparts of NS-NS/NS-BH Mergers
Importance of EM Detection:
• Place Merger into Astrophysical Context
Host Galaxy, Local Environment, & Binary Properties
• Improve Effective Sensitivity of G-Wave Detectors
(Kochanek & Piran 93)
Advanced LIGO Detection Rates Uncertain (~ 1 - 103 yr-1 )
• Cosmology: Redshift Measurement of H0
(e.g. Krolak & Shutz 87)
Electromagnetic Counterparts of NS-NS/NS-BH Mergers
Short-Duration
Gamma-Ray Burst
Blinnikov+84, Paczynski 86;
Goodman 86; Eichler+89
Supernova-Like
Transient Powered by
Radioactive Ejecta
Li & Paczynski 98; Kulkarni 05;
Rosswog 05; Metzger+08, 10
Bright, but Beamed
Dimmer, but Isotropic
Importance of EM Detection:
• Place Merger into Astrophysical Context
Host Galaxy, Local Environment, & Binary Properties
• Improve Effective Sensitivity of G-Wave Detectors
(Kochanek & Piran 93)
Advanced LIGO Detection Rates Uncertain (~ 1 - 103 yr-1 )
• Cosmology: Redshift Measurement of H0
(e.g. Krolak & Shutz 87)
•
B2FH: Type I SN light curves powered by 254Cf
•
Today: Type Ia SNe powered by 56Ni & 56Co
•
B2FH: Type I SN light curves powered by 254Cf
•
Today: Type Ia SNe powered by 56Ni & 56Co
Similar to a Supernova, but …
Faster Evolving
NS Merger Ejecta
How Supernovae Shine
(Arnett 1982)
Spherical ejecta w mass M, velocity v, thermal energy E = f Mc2, & opacity
}
R
M
r=
R=vt
V
t ~ krR
M
4p R 3
3
t diff ~ t R
(
)(
)
c
1/ 2
æ
ö
çM
÷
Emission peaks when t = tdiff t peak ~ 2 weeks v 4
-1
è M8ø
10 km s
1/ 2
1/ 2
E(t peak )
æ
ö
43
-1
f -5 v 4
çM
÷
Lpeak ~
~
10
ergs
s
-1
t peak
M
è
10
10 km s
8ø
(
-1/ 2
)
Type Ia SN:
v ~104 km s-1, Mej ~ M, fNiCo ~ 10-5 tpeak ~ week, L ~ 1043 erg s-1
NS Merger Ejecta:
v ~ 0.1 c, Mej ~ 10-2 M, f ~ ? tpeak~ 1 day, L ~ ???
How Supernovae Shine
(Arnett 1982)
Spherical ejecta w mass M, velocity v, thermal energy E = f Mc2, & opacity
}
R
M
r=
R=vt
V
t ~ krR
M
4p R 3
3
t diff ~ t R
(
)(
)
c
1/ 2
æ
ö
çM
÷
Emission peaks when t = tdiff t peak ~ 2 weeks v 4
-1
è M8ø
10 km s
1/ 2
1/ 2
E(t peak )
æ
ö
43
-1
f -5 v 4
çM
÷
Lpeak ~
~
10
ergs
s
-1
t peak
M
è
10
10 km s
8ø
(
-1/ 2
)
Type Ia SN:
v ~104 km s-1, Mej ~ M, fNiCo ~ 10-5 tpeak ~ week, L ~ 1043 erg s-1
NS Merger Ejecta:
v ~ 0.1 c, Mej ~ 10-2 M, f ~ ? tpeak~ 1 day, L ~ ???
Credit: M. Shibata (U Tokyo)
Tidal Tails (Dynamical Ejecta)
(e.g. Janka et al. 1999; Lee & Kluzniak 1999; Ruffert & Janka 2001; Rosswog et al. 2004;
Rosswog 2005; Shibata & Taniguchi 2006; Giacomazzo et al. 2009; Rezzolla et al. 2010;
Chawla et al. 2010)
Full GR / Simple EOS
Current Sims:
Mej ~ 0 - 10-1 M
Newtonian / Realistic EOS
Lee & Ramirez-Ruiz 07
Sources of Neutron-Rich
Ejecta
Tidal Tails (Dynamical Ejecta)
(e.g. Janka et al. 1999; Lee & Kluzniak 1999; Ruffert & Janka 2001; Rosswog et al. 2004;
Rosswog 2005; Shibata & Taniguchi 2006; Giacomazzo et al. 2009; Rezzolla et al. 2010;
Chawla et al. 2010)
Full GR / Simple EOS
Current Sims:
Mej ~ 0 - 10-1 M
Newtonian / Realistic EOS
Accretion Disk Outflows
Neutrino-Driven Winds (Early)
(McLaughlin & Surman 05; Surman+ 06, 08; BDM+08)
Thermonuclear-Driven Winds (Late)
(Metzger, Piro & Quataert 2008; Lee et al. 2009)
Mej ~ Mdisk/3 ~ 10-3 - 10-2 M
Neutron-Rich Freeze-Out Ye ~ 0.1-0.4
(BDM + 2009)
Lee et al. 2004
Lee & Ramirez-Ruiz 07
Sources of Neutron-Rich
Ejecta
How Supernovae Shine
(Arnett 1982)
Spherical ejecta w mass M, velocity v, thermal energy E = f Mc2, & opacity
}
R
M
r=
R=vt
V
t ~ krR
M
4p R 3
3
t diff ~ t R
(
)(
)
c
1/ 2
æ
ö
çM
÷
Emission peaks when t = tdiff t peak ~ 2 weeks v 4
-1
è M8ø
10 km s
1/ 2
1/ 2
E(t peak )
æ
ö
43
-1
f -5 v 4
çM
÷
Lpeak ~
~
10
ergs
s
-1
t peak
M
è
10
10 km s
8ø
(
-1/ 2
)
Type Ia SN:
v ~104 km s-1, Mej ~ M, fNiCo ~ 10-5 tpeak ~ week, L ~ 1043 erg s-1
NS Merger Ejecta:
v ~ 0.1 c, Mej ~ 10-2 M, f ~ ? tpeak~ 1 day, L ~ ???
Rapid Neutron Capture (R-Process)
Nucleosynthesis
Decompressing NS Matter A ~ 100 Nuclei + Free Neutrons
(Lattimer et al. 1977; Meyer 1989; Freiburghaus et al. 1999; Goriely et al. 2005)
Protons
Chart of the Nuclides
Neutrons
Rapid Neutron Capture (R-Process)
Nucleosynthesis
Decompressing NS Matter A ~ 100 Nuclei + Free Neutrons
(Lattimer et al. 1977; Meyer 1989; Freiburghaus et al. 1999; Goriely et al. 2005)
R-Process Network
Chart of the Nuclides
Protons
(Martinez-Pinedo 2008)
• neutron captures
(Rauscher & Thielemann 2000)
• photo-dissociations
• - and -decays
• fission reactions (Panov et al. 2009).
3rd
Abundance Peaks at
A ~ 130 and A ~ 195
2nd
BDM et al. 2010
Neutrons
Nucleosynthesis Calculations by G. Martinez-Pinedo & A. Arcones
Radioactive Heating of NS Merger Ejecta
Ye = 0.1
@ t ~ 1 day :
Ye = 0.1
t-1.2
• R-process & Ni heating similar
• ~1/2 Fission, ~1/2 -Decays
• Dominant -Decays:
132,134,135 I, 128,129Sb,129Te,135Xe
Nucleosynthesis Calculations by G. Martinez-Pinedo & A. Arcones
Radioactive Heating of NS Merger Ejecta
Ye = 0.1
@ t ~ 1 day :
Ye = 0.1
t-1.2
• R-process & Ni heating similar
• ~1/2 Fission, ~1/2 -Decays
• Dominant -Decays:
132,134,135 I, 128,129Sb,129Te,135Xe
fLP = 3 x 10-6
Results Robust to:
• ejecta composition
(Ye = 0.05 - 0.3)
• nuclear mass model
• outflow trajectory
(dynamically-ejected or wind-driven)
Light Curves
Color Evolution
Bolometric Luminosity
Blackbody Model
Monte Carlo Radiative Transfer (SEDONA; Kasen et al. 2006)
Peak Brightness MV= -15 @ t ~ 1 day for Mej = 10-2 M
Red Transient (Line Blanketing), Reddens in Time
CAVEAT: Fe composition assumed for opacity
does a pure r-process photosphere look like?
What
Metzger et al. 2010
“kilo-nova”
Three Detection Methods
1) Gravitational-Wave Triggered Follow-Up (See talks by Hughey,
Price & Kanner)
V < 22-24 to probe entire Advanced
LIGO merger volume (for MV = -15)
Positional Uncertainty ~ degrees
}
Wide-Field, Sensitive
Telescope (e.g. LSST)
Three Detection Methods
1) Gravitational-Wave Triggered Follow-Up
V < 22-24 to probe entire Advanced
LIGO merger volume (for MV = -15)
Positional Uncertainty ~ degrees
}
Wide-Field, Sensitive
Telescope (e.g. LSST)
Upper Limits
2) Short Gamma-Ray Burst Follow-Up
GRB 070724A
(Kocevski et al. 2009)
GRB 050509b
(Hjorth et al. 2005)
M ej < 0.1M8
M ej <10-3 M8
GRB 080503
(Perley, BDM, et al. 2009)
Possible Detection
Fundamental Obstacle? Bright Optical Afterglow
Early Follow-Up Observations of Short GRBs (courtesy Edo Berger)
Triangles - Upper Limits
Solid Squares - Detections
(known redshift)
Open Squares - Detections
(with likely redshift)
Open Squares w lines - Detections
(unknown redshift range)
M ej =10-2 M8
M ej =10-3 M8
GRB 080503:
Candidate Kilonova
(Perley, BDM et al. 2009)
Optical
Rebrightenin
g @ t ~ 1 day
Wheres the Host
Galaxy?
z = 0.561
Kilonova Parameters: v ~ 0.1 c, Mej ~ few 10-2 M , z ~ 0.1
Three Detection Methods
1) Gravitational-Wave Triggered Follow-Up
V < 22-24 to probe entire Advanced
LIGO merger volume (for MV = -15)
Positional Uncertainty ~ degrees
}
Wide-Field, Sensitive
Telescope (e.g. LSST)
Upper Limits
2) Short Gamma-Ray Burst Follow-Up
GRB 070724A
(Kocevski et al. 2009)
GRB 050509b
(Hjorth et al. 2005)
M ej < 0.1M8
M ej <10-3 M8
GRB 080503
(Perley, BDM, et al. 2009)
Possible Detection (but no redshift)
Fundamental Obstacle? Bright Optical Afterglow
3) “Blind” Optical Transient Surveys
(e.g. Palomar Transient Factory, Pan-STARRs, LSST) See talks by Quimby, Kasliwal
N˙ merge ~ 10-4 yr -1, Mej =10-2 M8 PTF ~ 1 yr
-1
& LSST ~ 103 yr-1
Conclusions
Direct gravitational wave detection plausible within the decade
Maximizing science requires identifying EM counterpart
Remnant accretion disk may power short GRB
but… beamed emission may limit use as gravitational wave beacon
Two sources of neutron-rich ejecta from NS Mergers
Dynamically-Ejected Tidal Tail (uncertain, but may be small < 10-3 M)
Recombination Disk Winds (~30% of remnant disk mass or ~10-3-10-2 M)
Optical transient powered by decaying r-process elements
Nuclear Reaction Network: fLP ~ 3 x 10-6 , Robust to Uncertainties
Radiative Transfer: Short Duration (~1 day), Low Luminosity (MV ~ -15)
& Red Colors (UV Line Blanketing)
Detection & follow-up will require carefully-planned search strategy
& close cooperation btw astronomy & gravitational wave community
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