Red or blue? A potential kilonova imprint of the delay until black hole formation following a neutron star merger

By B. Metzger, R. Fern'andez. 2014

310 citations recorded by the source corpus.

Mergers of binary neutron stars (NSs) usually result in the formation of a hypermassive neutron star (HMNS). Whether- and when this remnant collapses to a black hole (BH) depends primarily on the equation of state and on angular momentum transport processes, both of which are uncertain. Here we show that the lifetime of the merger remnant may be directly imprinted in the radioactively powered kilonova emission following the merger. We employ axisymmetric, time-dependent hydrodynamic simulations of remnant accretion disks orbiting a HMNS of variable lifetime, and characterize the effect of this delay to BH formation on the disk wind ejecta. When BH formation is relatively prompt (~ 100 ms), outflows from the disk are sufficiently neutron rich to form heavy r-process elements, resulting in ~ week-long emission with a spectral peak in the near-infrared (NIR), similar to that produced by the dynamical ejecta. In contrast, delayed BH formation allows neutrinos from the HMNS to raise the electron fraction in the polar direction to values such that potentially Lanthanide-free outflows are generated. The lower opacity would produce a brighter, bluer, and shorter-lived ~ day-long emission (a `blue bump') prior to the late NIR peak from the dynamical ejecta and equatorial wind. This new diagnostic of BH formation should be useful for events with a signal to noise lower than that required for direct detection of gravitational waveform signatures.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8d6db16ad9248b94878324ca3c27c2a3505e59ef

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Citations in the corpus

Neutron Star Extreme Matter Observatory: A kilohertz-band gravitational-wave detector in the global network (2020, background): “…(Zhang 2018), and the existence and lifetime of the remnant will reveal the impact of neutrino radiation on heavy-element formation through the rapid neutroncapture process in kilonovae (Metzger & Fernández 2014; Martin et al. 2015; Fernández et al. 2019; Kawaguchi, Shibata, & Tanaka 2020).”
NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS (2015, background): “Although at this point it is difficult to draw any quantitative conclusions due to limitations of our model, our results suggest a possibility to use the position and duration of optical transients as proxies for the time of black hole formation (see also Metzger & Fernández (2014)).”
Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW170817 (2017, background): “The different types of merger outcomes are predicted to create qualitatively different electromagnetic (EM) signals (e.g. Bauswein et al. 2013; Metzger & Fernández 2014).”
Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers (2017, methodology): “Upon collapse of the HMNS to a BH, the boundary layer is swallowed, and a rarefaction wave moves outward from the inner boundary, quenching the thermal outflow (cf. Figure 3 of Metzger & Fernández 2014).”
A Magnetar Origin for the Kilonova Ejecta in GW170817 (2018, background): “25 (Metzger & Fernández 2014).”
Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, methodology): “The models are carried out in a modified version of FLASH3 (Fryxell et al. 2000; Dubey et al. 2009) that has been equipped with the physics required to simulate merger remnant accretion disks (Fernández & Metzger 2013a,b; Metzger & Fernández 2014; F15).”
Kilonova light curves from the disc wind outflows of compact object mergers (2014, methodology): “We make use of the hydrodynamical disc wind simulations from Metzger & Fernández (2014) and Fernández et al. (2015), as enumerated in Table 1.”
AT 2017gfo: An Anisotropic and Three-component Kilonova Counterpart of GW170817 (2017, background): “If during the merger a disk has formed, on its longer lifetime (100s ms) the spreading due to viscous processes and the subsequent nuclear recombination unbind a fraction of the disk (Metzger et al. 2009; Fernández & Metzger 2013; Metzger & Fernández 2014; Just et al. 2015).”
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta (2017, background): “While winds from the accretion disk around the post-merger remnant can eject the requisite amount of mass (e.g. Fernández & Metzger 2013; Metzger & Fernández 2014; Perego et al. 2014; Siegel & Metzger 2017), the predicted wind velocities are too low (< 0.1c).”
Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers (2017, methodology): “…accretion flow have been performed under the assumption of hydrodynamics, adopting an effective hydrodynamical α−viscosity (Shakura & Sunyaev 1973) in place of self-consistent MHD turbulence (Fernández & Metzger 2013; Metzger & Fernández 2014; Just et al. 2015; Fernández et al. 2015; ?)”
The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, background): “…Smartt et al. 2017; Tanvir et al. 2017; Villar et al. 2017), particularly the inferred presence of lanthanide-rich material created from very neutron-rich ejecta (neutrinos from a long-lived neutron star remnant would transform outflowing neutrons back into protons; see Metzger & Fernández 2014).”
J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817 (2017, background): “…by guest on 26 July 2018 elements in the Universe as emission properties reflect the ejected mass and abundances of r-process elements (e.g., Kasen et al. 2013; Barnes & Kasen 2013; Tanaka & Hotokezaka 2013; Tanaka et al. 2014; Metzger & Fernández 2014; Kasen et al. 2015).”
Neutron-powered precursors of kilonovae (2014, background): “The resulting low photospheric temperature at late times produces emission that peaks in the far infrared (Barnes & Kasen 2013; althoug , see Metzger & Fernández 2014) where follow-up telescopes ar less sensitive.”
Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, background): “Increased interest due to the possibility of an additional, bluer component from secondary outflows has resulted in a number of recent wind studies (Dessart et al. 2009; Grossman et al. 2014; Perego et al. 2014; Martin et al. 2015; Metzger & Fernández 2014; Just et al. 2015; Fernández et al. 2015).”
Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations (2018, background): “Alternatively, as with the red ejecta, the blue ejecta could originate from an accretion disc outflow (e.g. Metzger & Fernandez 2014; Perego et al. 2014); however, the high velocity is incompatible with both hydrodynamical and MHD simulations (e.g. Fan, Messenger & Heng 2014; Siegel & Metzger 2017).”
Neutron-star Radius Constraints from GW170817 and Future Detections (2017, background): “…this merger outcome tends to produce larger ejecta masses as compared to a direct collapse (Bauswein et al. 2013b; Hotokezaka et al. 2013; Fernández & Metzger 2013; Metzger & Fernández 2014; Perego et al. 2014; Siegel et al. 2014; Wanajo et al. 2014; Just et al. 2015; Sekiguchi et al. 2016).”