OPACITIES AND SPECTRA OF THE<i>r</i>-PROCESS EJECTA FROM NEUTRON STAR MERGERS

Kasen, Daniel; Badnell, N. R.; Barnes, Jennifer

doi:10.1088/0004-637x/774/1/25

Cited by 580 publications

(842 citation statements)

References 57 publications

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“…For example, neutron-rich outflows from the NS merger form heavy elements via the r-process and undergo radioactive decay, resulting in a kilonova transient (Li & Paczyński 1998). In the absence of a long-lived magnetar, the signal is expected to peak in the near-IR band on ∼week timescales due to the large opacities of the heavy elements produced Kasen et al 2013;Tanaka & Hotokezaka 2013;Grossman et al 2014;Fontes et al 2015). In contrast, the large neutrino luminosity from a long-lived magnetar may inhibit the formation of very heavy elements, resulting in a bluer kilonova that peaks at optical wavelengths on ∼day timescales (Metzger & Fernández 2014;Kasen et al 2015).…”

Section: Discussionmentioning

confidence: 99%

Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts

Fong

Metzger

Berger

et al. 2016

ApJ

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The merger of a neutron star (NS) binary may result in the formation of a rapidly spinning magnetar. The magnetar can potentially survive for seconds or longer as a supramassive NS before collapsing to a black hole if, indeed, it collapses at all. During this process, a fraction of the magnetar's rotational energy of ∼10 53 erg is transferred via magnetic spin-down to the surrounding ejecta. The resulting interaction between the ejecta and the surrounding circumburst medium powers a year-long or greater synchrotron radio transient. We present a search for radio emission with the Very Large Array following nine short-duration gamma-ray bursts (GRBs) at rest-frame times of ≈1.3-7.6 yr after the bursts, focusing on those events that exhibit early-time excess X-ray emission that may signify the presence of magnetars. We place upper limits of 18-32 μJy on the 6.0 GHz radio emission, corresponding to spectral luminosities of (0.05-8.3)×10 39 erg s −1 . Comparing these limits to the predicted radio emission from a long-lived remnant and incorporating measurements of the circumburst densities from broadband modeling of short GRB afterglows, we rule out a stable magnetar with an energy of 10 53 erg for half of the events in our sample. A supramassive remnant that injects a lower rotational energy of 10 52 erg is ruled out for a single event, GRB 050724A. This study represents the deepest and most extensive search for long-term radio emission following short GRBs to date, and thus the most stringent limits placed on the physical properties of magnetars associated with short GRBs from radio observations.

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Section: Discussionmentioning

confidence: 99%

Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts

Fong

Metzger

Berger

et al. 2016

ApJ

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“…Gamma-ray bursts and r-process production are most likely in the case the neutron star is tidally disrupted, and radioactive decay in unbound neutron-rich ejecta could produce an isotropic optical (Roberts et al 2011;Metzger & Berger 2012) or infrared (Kasen et al 2013) transient. The potential for mass ejection depends on whether or not tidal effects are strong enough for the neutron star to be disrupted before reaching the innermost stable circular orbit (R ISCO ) of the black hole.…”

Section: Disk Masses and Energetics Of Compact Star Mergersmentioning

confidence: 99%

Constraining the Symmetry Parameters of the Nuclear Interaction

Lattimer

Lim

2013

ApJ

567

629

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One of the major uncertainties in the dense matter equation of state has been the nuclear symmetry energy. The density dependence of the symmetry energy is important in nuclear astrophysics, as it controls the neutronization of matter in core-collapse supernovae, the radii of neutron stars and the thicknesses of their crusts, the rate of cooling of neutron stars, and the properties of nuclei involved in r-process nucleosynthesis. We show that fits of nuclear masses to experimental masses, combined with other experimental information from neutron skins, heavy ion collisions, giant dipole resonances, and dipole polarizabilities, lead to stringent constraints on parameters that describe the symmetry energy near the nuclear saturation density. These constraints are remarkably consistent with inferences from theoretical calculations of pure neutron matter, and, furthermore, with astrophysical observations of neutron stars. The concordance of experimental, theoretical, and observational analyses suggests that the symmetry parameters S v and L are in the range 29.0-32.7 MeV and 40.5-61.9 MeV, respectively, and that the neutron star radius, for a 1.4 M star, is in the narrow window 10.7 km < R < 13.1 km (90% confidence). We can also set tight limits to the size of neutron star crusts and the fractional moment of inertia they contain, as well as the overall moment of inertia and quadrupole polarizability of 1.4 M stars. Our results also have implications for the disk mass and ejected mass of compact mergers involving neutron stars.

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“…In addition, it is also important to know the optical opacities for r-process material as they determine the timescale for photons to escape from the inner opaque region of the ejecta. It has been suggested that a major source of opacity is due to the presence of lanthanides (Z = 57-71, A ≈ 139-176) [74][75][76] in the r-process ejecta. Due to their large photon opacities the lanthanides delay the light curve luminosity peak to timescales of a week.…”

Section: E Implications For Kilonova Observationsmentioning

confidence: 99%

Nuclear robustness of therprocess in neutron-star mergers

et al. 2015

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We have performed r-process calculations for matter ejected dynamically in neutron star mergers based on a complete set of trajectories from a three-dimensional relativistic smoothed particle hydrodynamic simulation with a total ejected mass of ∼ 1.7 × 10 −3 M . Our calculations consider an extended nuclear network, including spontaneous, β-and neutron-induced fission and adopting fission yield distributions from the ABLA code. In particular we have studied the sensitivity of the r-process abundances to nuclear masses by using different models. Most of the trajectories, corresponding to 90% of the ejected mass, follow a relatively slow expansion allowing for all neutrons to be captured. The resulting abundances are very similar to each other and reproduce the general features of the observed r-process abundance (the second and third peaks, the rare-earth peak and the lead peak) for all mass models as they are mainly determined by the fission yields. We find distinct differences in the predictions of the mass models at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r-process nuclei around neutron number N = 130. In all simulations, we find that the second peak around A ∼ 130 is produced by the fission yields of the material that piles up in nuclei with A 250 due to the substantially longer beta-decay half-lives found in this region. The third peak around A ∼ 195 is generated in a competition between neutron captures and β decays during r-process freeze-out. The remaining trajectories, which contribute 10% by mass to the total integrated abundances, follow such a fast expansion that the r process does not use all the neutrons. This also leads to a larger variation of abundances among trajectories as fission does not dominate the r-process dynamics. The resulting abundances are in between those associated to the r and s processes. The total integrated abundances are dominated by contributions from the slow abundances and hence reproduce the general features of the observed r-process abundances. We find that at timescales of weeks relevant for kilonova light curve calculations, the abundance of actinides is larger than the one of lanthanides. This means that actinides can be even more important than lanthanides to determine the photon opacities under kilonova conditions. Moreover, we confirm that the amount of unused neutrons may be large enough to give rise to another observational signature powered by their decay.

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OPACITIES AND SPECTRA OF THEr-PROCESS EJECTA FROM NEUTRON STAR MERGERS

Cited by 580 publications

References 57 publications

Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts

Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts

Constraining the Symmetry Parameters of the Nuclear Interaction

Nuclear robustness of therprocess in neutron-star mergers

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