The cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers

By O. Gottlieb, E. Nakar, T. Piran. 2017

156 citations recorded by the source corpus.

Short Gamma-Ray Bursts (SGRBs) are believed to arise from compact binary mergers (either neutron star-neutron star or black hole-neutron star). If so their jets must penetrate outflows that are ejected during the merger. As a jet crosses the ejecta it dissipates its energy, producing a hot cocoon which surrounds it. We present here 3D numerical simulations of jet propagation in mergers' outflows and we calculate the resulting emission. This emission consists of two components: the cooling emission, the leakage of the thermal energy of the hot cocoon, and the cocoon macronova that arises from the radioactive decay of the cocoon's material. This emission gives a brief (~ one hour) blue, wide angle signal. While the parameters of the outflow and jet are uncertain, for the configurations we have considered the signal is bright (~ -14 $-$ -15 absolute magnitude) and outshines all other predicted UV-optical signals. The signal is brighter when the jet breakout time is longer and its peak brightness does not depend strongly on the highly uncertain opacity. A rapid search for such a signal is a promising strategy to detect an electromagnetic merger counterpart. A detected candidate could be then followed by deep IR searches for the longer but weaker macronova arising from the rest of the ejecta.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/1eb8ade62d28e227eadabf34f7dcca0f51656d94

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In Astronomy and Astrophysics

1. B. Metzger
2. E. Berger
3. E. Quataert
4. R. Fern'andez
5. D. Kasen
6. Bing Zhang
7. T. Thompson
8. W. Fong

Citations in the corpus

• Origin of the heaviest elements: The rapid neutron-capture process (2019, background): “surrounds the GRB jet as it crosses the ejecta (Gottlieb et al., 2018).”
• Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, methodology): “Finally, evaluating the feasibility of models that rely on the interaction of a jet with the dynamical ejecta (such as models involving cocoon emission; e.g. Nagakura et al. 2014; Lazzati et al. 2017; Gottlieb et al. 2018) requires proper initial conditions for all merger remnant components.”
• J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817 (2017, background): “Or possibly, a higher luminosity can be accounted for by an additional energy source, such as the cocoon emission (Gottlieb et al. 2018).”
• The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, methodology): “This model was favored by Gottlieb et al. (2018); Hallinan et al. (2017); Kasliwal et al. (2017); Mooley et al. (2017); Nakar & Piran (2018).”
• A Magnetar Origin for the Kilonova Ejecta in GW170817 (2018, background): “1–1 s (e.g., Metzger et al. 2008b) or an accretion disk of lifetime ∼1 s (e.g., Fernández & Metzger 2013), and is not a unique prediction of a (failed or successful) ultrarelativistic jet (Gottlieb et al. 2018).”