Gravitational Waves and Electromagnetic Signals from a Neutron Star Merger

Transcription

1 Gravitational Waves and Electromagnetic Signals from a Neutron Star Merger

2 end-to-end physics of NS mergers GRB + afterflow binary stellar evolution ( years) Final inspiral (minutes) gravitational waves post-merger accretion (seconds) hydrodynamics, gravity, neutrino physics,nuclear reactions, magnetic fields radioactivity (days-weeks) nuclear decay chains (alpha, beta, gamma, fission) thermalization optical/ir kilonova merger dynamics (miliseconds) hydrodynamics, general relativity, nuclear equation of state, neutrino physics, nucleosynthesis (seconds) r-process reaction networks, nuclear data inputs radiation transport (days weeks) Time-dependent spectral Boltzmann transport Atomic microphysics

3 dynamical t ~ milliseconds S. Rosswog tidal tail ejecta M ~ Msun v ~ 0.2c - 0.3c very neutron rich, Ye 0.1 squeezed polar ejecta M ~ Msun v ~ 0.2c - 0.3c less neutron rich Ye 0.25 MERGER MASS EJECTION Bauiswein post-merger t ~ seconds Fernandez &Metzger 2013 disk wind ejecta M ~ Msun v ~ 0.05c - 0.1c range of Ye =

4 neutrino irradiation of NS merger ejecta weak interactions drive Ye closer to 0.5 (e.g., Metzger & Fernandez 2013) neutrino energy density neutrino mean energy NS $ e + n $ p + e e + p $ n + e + richers, kasen, et al 2015

5 number of protons Heavy element production via rapid-neutron capture very neutron rich ejecta Ye ~< 0.25 number of neutrons Nuclear reaction network calculations Jonas Lippuner less neutron rich ejecta Ye >~ 0.25

6 Abundances from r-process nucleosynthesis reaction networks calculations for fixed entropy & expansion time light r-process heavy r-process

7 Schematic view of NS merger ejecta shocked polar v ~ 0.2c-0.3c M < 0.01 M light r-process disk wind mixed composition v ~ 0.1c M ~ M tidal tails v ~ 0.2c-0.3c M < 0.01 M heavy r-process neutron star + neutron star prompt collapse to black hole

8 Radioactive decay and thermalization radioactive power rate to Roberts et al rate ~ t -1.3 Radioactive power Metzger+2010 Roberts+2011 isotopic contributions time in days fraction Decay products and thermalization efficiencies thermalization efficiency Barnes, DK et al efficiency ~ t -1 - t -2 Thermalization efficiency Barnes, Kasen, Wu, Martinez-Pineda 2016 time in days

9 Radioactive kilonova light curve models Type Ia SN model kilonova models

10 modeling kilonova light curves and spectra solution to the radiation transport (Boltzmann) equation absorption emission scattering = photon field specific intensity = opacity coefficient = emissivity and set primarily by numerous blended atomic line transitions depends on ionization/excitation state of gas (level populations assumed to be local thermodynamic equilibrium) Transport solved by Monte Carlo methods (Sedona code) e.g,. Kasen+2006, Roth and Kasen (2015)

11 opacity of r-process kilonova ejecta bound-bound (lines) electron scattering bound-free (photoionization) free-free (bremsstrahlung)

12 s-shell (g=2) r-process opacity and atomic complexity limited experimental line data requires atomic structure modeling p-shell (g=6) d-shell (g=10) f-shell (g=14)

13 r-process opacity and atomic complexity Half-filled shells have more complex configurations Atomic line/level data is still sparse (especially in infrared) New atomic-structure calculations cover the statistical properties of all r-process species but uncertainties remain in details (kasen+ in prep) approximate # of atomic levels d p s f atomic number Z lanthanides actinides

14 Level energy distributions - singly ionized species atomic structure calculations of all r-process species w/ autostructure code thermally populated states Z = 60 Z = 64 Z = 42 Z = 26

15 lanthanides (f-shell) kilonova opacity from atomic structure modeling (d-shell) kasen T = 5000 K rho = g cm -3

16 Model kilonova spectra dependence on lanthanide fraction kasen, badnell and barnes 2013, barnes & kasen 2013, kasen+2017 SSecific luminoviwy (10 41 eug V 1 µm 1 ) UV oswical infuaued X lan =10 5 X lan =10 4 X lan =10 1 X lan =10 1 model spectrum at 4.5 days after merger WavelengWh (micuon)

17 Model kilonova light curves: dependence on lanthanide fraction kasen, badnell and barnes 2013, barnes & kasen 2013, kasen+2017 Log 10 bolometrlc lumlnoslty (erg s 1 ) X lan )10 4 X lan )10 1 rddlodctlve hedtlng rdte bolometric light curve DDys slnce merger

18 Abundances from r-process nucleosynthesis reaction networks calculations for fixed entropy & expansion time light r-process heavy r-process kasen+2015 lanthanides

19 kilonova SSS17a bolometric light curve radioactivity: Lippuner & Roberts 2015 Q(t) of 0.02 Msun

20 kilonova AT2017gfo bolometric light curve radioactivity: Lippuner & Roberts 2015 thermalization: Barnes Q(t)*f(t) of 0.04 Msun

21 Multi-wavelength photometry of SSS17a Villar+2017

22 kilonova SSS17a bolometric light curve SSS17a bolometric bolometric compilation: Waxman models: Kasen+2017 lanthanide rich lanthanide poor

23

24 kilonova AT2017gfo day 1.5

25 kilonova AT2017gfo day 1.5

26 kilonova SSS17a day 2.5 data Pian+2017 x-shooter, models Kasen+2017 light + heavy r-process model rf

27 Model spectrum dependence on composition features are Doppler-broadened blends of multiple lines 2.5 cerium 10 5elaWive flux F λ plus RfffseW nerdymium 0 nerdymium 10 defaulw (srlar) WavelengWh (micrrn)

28 Spectral determination of ejecta velocity (consistent with blackbody emitting radius, e.g., Drout+17, Troja+17) b heavy r-prrcess W 4.5 days Kasen+2017 v 0.03c v 0.10c v 0.20c v 0.30c WavelengWh (micrrns)

29 GW170817: Some questions Are neutron star mergers a site (the site) of the r-process? Blue kilonova (light r-process) M ~ Msun - v ~ 0.3c; Xlan < 10-4 Red kilonova (heavy r-process) M ~ 0.04 Msun - v ~ 0.1c, Xlan ~ 10-2 Merger rate (from LIGO): Rm ~ 1 per years per galaxy Can potentially account for all r-process in galaxy Mgalaxy = 5 x 10 3 Msun = fstar x Mm x Rm x tgal But ejecta masses and rates are certain. Was the 1 event typical?