Off-axis emission of short γ-ray bursts and the detectability of electromagnetic counterparts of gravitational-wave-detected binary mergers

By D. Lazzati, A. Deich, B. Morsony, Jared C. Workman. 2016

146 citations recorded by the source corpus.

We present calculations of the wide angle emission of short-duration gamma-ray bursts from compact binary merger progenitors. Such events are expected to be localized by their gravitational wave emission, fairly irrespective of the orientation of the angular momentum vector of the system, along which the gamma-ray burst outflow is expected to propagate. We show that both the prompt and afterglow emission are dim and challenging to detect for observers lying outside of the cone within which the relativistic outflow is propagating. If the jet initially propagates through a baryon contaminated region surrounding the merger site, however, a hot cocoon forms around it. The cocoon subsequently expands quasi-isotropically producing its own prompt emission and external shock powered afterglow. We show that the cocoon prompt emission is detectable by Swift BAT and Fermi GBM, We also show that the cocoon afterglow peaks a few hours to a few days after the burst and is detectable for up to a few weeks at all wavelengths. The timing and brightness of the transient are however uncertain due to their dependence on unknown quantities such as the density of the ambient medium surrounding the merger site, the cocoon energy, and the cocoon Lorentz factor. For a significant fraction of the gravitationally-detected neutron-star-binary mergers, the cocoon afterglow could possibly be the only identifiable electromagnetic counterpart, at least at radio and X-ray frequencies.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/35c4cd2eb8fa260c05a6d897b48a14aa688c1932

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Citations in the corpus

The cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers (2017, background): “The properties of the cocoon that we find are very different than the spherical outflow with Γ = 10 assumed by MNRAS 000, 1–9 (2017) Lazzati et al. (2017) and therefore their light curve predictions are also different than our findings here.”
Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW170817 (2017, background): “This could indicate that we are observing the GRB jet well outside of its core (e.g. Kathirgamaraju et al. 2017; Lazzati et al. 2017).”
The evolution of the X-ray afterglow emission of GW 170817 / GRB 170817A in XMM-Newton observations (2018, background): “The propagation through such ambient material is likely to play a major role in shaping the jet angular distribution of energy and terminal Lorentz factor at breakout (see e.g. the simulations by Lazzati et al. 2017b).”
A cocoon shock breakout as the origin of the γ-ray emission in GW170817 (2017, background): “Any relativistic jet will have to path through this mass (see Nagakura et al. 2014; Murguia-Berthier et al. 2014; Duffell et al. 2015; Lazzati et al. 2017a; Gottlieb et al. 2017 for jet propagation studies).”
The Binary Neutron Star Event LIGO/Virgo GW170817 160 Days after Merger: Synchrotron Emission across the Electromagnetic Spectrum (2018, methodology): “…successful structured jet scenario that we support here and the choked-jet/stratified ejecta scenarios have been proposed, including VLBI imaging and the acquisition of a larger sample of GW events with electromagnetic counterparts (Hallinan et al. 2017; Lazzati et al. 2017c; Mooley et al. 2017).”
The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars (2017, background): “…but the absence of a normal GRB afterglow in subsequent monitoring (e.g., in X-rays; Evans et al. 2017) instead suggests the possibility of some kind of off-axis emission mechanism, such as may be produced by a shocked cocoon around the primary jet (e.g., Gottlieb et al. 2017; Lazzati et al. 2017).”
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.”
AT 2017gfo: An Anisotropic and Three-component Kilonova Counterpart of GW170817 (2017, background): “The presence of a BC might be also explained by other mechanisms, for example by the energy deposition of a relativistic jet in a cocoon of ejecta (Lazzati et al. 2017; Bromberg et al. 2017).”
An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A (2017, background): “A kT ≈ 10 keV temperature blackbody spectrum is in agreement with expectations from such a scenario (Lazzati et al. 2017).”