Kilonova signatures and the r -process FRIB and the GW170817 kilonova Jennifer Barnes NASA Einstein Fellow Columbia University
mergers: a stellar danse macabre final few orbits: strong GW source Image: NASA e.g. Lattimer & Schramm 1974, 1976 Li & Paczynski 1998 Image credit: Daniel Price (U/Exeter) and Stephan Rosswog (Int. U/Bremen)
mergers: a stellar danse macabre merger: neutron final few orbits: star is partially strong GW source disrupted, central remnant forms Image: NASA e.g. Lattimer & Schramm 1974, 1976 Li & Paczynski 1998 Image credit: Daniel Price (U/Exeter) and Stephan Rosswog (Int. U/Bremen)
mergers: a stellar danse macabre merger: neutron final few orbits: star is partially strong GW source disrupted, central remnant forms Image: NASA ejecta: some material is escapes; some is bound e.g. Lattimer & Schramm 1974, 1976 Li & Paczynski 1998 Image credit: Daniel Price (U/Exeter) and Stephan Rosswog (Int. U/Bremen)
mergers: a stellar danse macabre merger: neutron final few orbits: star is partially strong GW source disrupted, central remnant forms Image: NASA ejecta: some final: a central material is NS or BH, an escapes; accretion disk, some is unbound ejecta bound e.g. Lattimer & Schramm 1974, 1976 Li & Paczynski 1998 Image credit: Daniel Price (U/Exeter) and Stephan Rosswog (Int. U/Bremen)
radioactive transients are probes of the r -process “kilonova” • Mildly relativistic unbound material • Heavy elements are synthesized An expanding cloud heated by radioactive decays
X-ray UV Let’s Optical zoom in IR Radio 10 -2 10 -1 10 0 10 1 t-t c (days) transient ad. from ALV + EM Partners 17 source detected in galaxy NGC 4993
X-ray UV Let’s Villar+17 Optical zoom in IR Radio log 10 luminosity - 10 -2 10 -1 10 0 10 1 t-t c (days) photon energy transient ad. from ALV + EM Partners 17 ∝ source detected in galaxy + NGC 4993 0 5 10 15 20 25 30 days since merger
ingredients for a kilonova model (bolometric) light curves ˙ E rad ( t ) Energy from radioactivity ergs/s time
ingredients for a kilonova model (bolometric) light curves ˙ E rad ( t ) Energy from radioactivity ergs/s E ffi ciency of thermalization time
ingredients for a kilonova model (bolometric) light curves ˙ E rad ( t ) Energy from radioactivity ergs/s Opacity (composition) sets the di ff usion time/ time for the ejecta to become optically thin E ffi ciency of thermalization time
ingredients for a kilonova model (bolometric) light curves colors & spectra ˙ E rad ( t ) • Quasi-blackbody with Energy from temperature set by radioactivity the net e ff ect of radioactivity, thermalization, photon absorption/ emission, and cooling ergs/s Opacity (composition) • Line-blanketing can sets the di ff usion time/ a ff ect the spectrum time for the ejecta to • Individual features become optically thin correspond to E ffi ciency of thermalization particular atoms or ions time
Because there are many contributing ˙ decays, follows a ~power law E rad ( t ) E rad ( t ) = fc 2 ˙ The expression Beta decay t Fission was first derived analytically Total erg g -1 s -1 (Li & Paczy ń ski 1998; see also Hotokezaka+17) The basic behavior has Metzger +2010 since been borne out by nuclear network calculations log (days) • however, the power-law erg g -1 s -1 behavior may break down at late times. Roberts +2011 log (days)
opacity is composition-dependent The r -process produces elements with atomic structures that are unique among explosively-synthesized compositions. Elements made by SNe the r -process mergers Lanthanides Actinides
opacity is composition-dependent • Bound-bound opacity (cm 2 g -1 ) sets the photon mean free path. absorption if ∆ E ≈ hc = λ cross section photon photon wavelength τ = π e 2 1 λ i m e cf osc n 1 t exp λ 0 X � 1 − e − τ i � κ exp ( λ c ) = ∆ λ c ρ ct exp i Sobolev optical depth sets The expansion opacity interaction probability with a determines the effective particular line continuum opacity
opacity is composition-dependent • Atomic structure modeling compensates for missing data • Lanthanides/actinides increase the opacity bound-bound expansion opacity (cm 2 g -1 ) FeII (Z = 26) many-body 10 2 CeII (Z = 58) Quantum NdII (Z = 60) Lanthanides Mechanical OsII (Z = 76) 10 1 system 10 0 d -block elements lines, levels, 10 -1 oscillator 10 -2 strengths 10 -3 synthetic T = 5000 K JB & Kasen 2013 10 -4 opacities rho = 10 -14 g cm -3 Kasen, Badnell, & JB 2013 10 -5 5,000 10,000 15,000 20,000 25,000 angstroms
opacity is composition-dependent The r -process produces elements with atomic structures that are unique among explosively-synthesized compositions. Simple analytic estimates: g ! N lev ≈ n !( g − n )! N lines ≈ N 2 no. of electrons n = lev g = 2(2 l + 1) SNe s -shell (2 e - ) p -shell (6 e - ) d -shell (10 e - ) mergers f -shell (14 e - ) Lanthanides Actinides
higher opacities lead to longer, dimmer, redder light curves ◆ 1 / 2 ✓ M κ adiabatic losses: E phot ∼ t − 1 diffusion time: t di ff ≈ vc line blanketing at optical wavelengths Kasen, Metzger, JB +17 42 2.0 more heavy X lan = 10 − 5 r -process X lan = 10 − 4 spectrum at 4.5 days X lan = 10 − 2 1.5 log 10 Luminosity X lan = 10 − 1 41 flux 1.0 0.5 bolometric light curve 40 0 2 4 6 8 10 0.5 1.0 1.5 2.0 2.5 3.0 days since merger microns
kilonova emission is tied to the strength of the r -process! fewer free n per seed more free n per seed p Y e = p + n Fe-group elements heavy light r -process r -process Lippuner & Roberts 2015
kilonova emission is tied to the strength of the r -process! more weak interactions fewer weak interactions fewer free n per seed more free n per seed p Y e = p + n Fe-group elements heavy light r -process r -process Lippuner & Roberts 2015
kilonova emission is tied to the strength of the r -process! more weak interactions fewer weak interactions dynamically fewer free n per seed more free n per seed squeezed tidally p stripped Y e = p + n Fe-group elements disk outflows heavy light r -process r -process Lippuner & Roberts 2015
spectral identification: the next frontier!
the r -process and kilonova thermalization (bolometric) light curves ˙ E rad ( t ) Energy from radioactivity ˙ E therm Radioactive ergs/s energy converted to thermal photons time
the r -process and kilonova thermalization (bolometric) light curves thermalization ˙ E rad ( t ) e ffi ciency depends on: Energy from • decay mode radioactivity • decay spectra • composition (cross- ˙ sections) E therm • ejecta mass, velocity Radioactive ergs/s energy converted to thermal photons time
thermalization depends on decay mode -decay β Thermalization e ffi ciencies per particle β γ fission fragments β -particles 1.0 α -particles ν 0.8 γ -rays α -decay 0.6 f ( t ) α 0.4 fission 0.2 0.0 0 5 10 15 20 25 30 fragments Days
At late times, a few decays may dominate the heating α Fissioning or -decaying nuclei with weeks or months τ ∼ could substantially a ff ect the luminosity • High Q -values (compared to -decay) β • E ffi cient thermalization Fraction of energy in each channel 10 0 10 -1 Californium-254 10 -2 Q SF ≈ 200 days -decay β 10 -3 MeV τ 1/2 = 60.5 α -decay 10 -4 spont. fiss. 10 -5 data courtesy Y. Zhu 10 2 10 3 10 4 10 5 10 6 10 7 log 10 (time)
At late times, a few decays may dominate the heating α Fissioning or -decaying nuclei with weeks or months τ ∼ could substantially a ff ect the luminosity • High Q -values (compared to -decay) β • E ffi cient thermalization
Heating from spontaneous fission of Cf-254 impacts kilonova light curves Energy Released Light Curves Observed heating (ergs s -1 g -1 ) Zhu+2018 absolute magnitude Zhu+2018 time (days) log 10 days Late-time light curves can probe the production of the heaviest nuclei and give more detailed information about the composition
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