Resonant shattering flares as multimessenger probes of the nuclear symmetry energy

Abstract

The behaviour of the nuclear symmetry energy near saturation density is important for our understanding of dense nuclear matter. This density dependence can be parameterised by the nuclear symmetry energy and its derivatives evaluated at nuclear saturation density. In this work we show that the core-crust interface mode of a neutron star is sensitive to these parameters, through the (density-weighted) shear-speed within the crust, which is in turn dependent on the symmetry energy profile of dense matter. We calculate the frequency at which the neutron star quadrupole (ℓ = 2) crust-core interface mode must be driven by the tidal field of its binary partner to trigger a Resonant Shattering Flare (RSF). We demonstrate that coincident multimessenger timing of an RSF and gravitational wave chirp from a neutron star merger would enable us to place constraints on the symmetry energy parameters that are competitive with those from current nuclear experiments.

Resonant Shattering Flares in Black Hole-Neutron Star and Binary Neutron Star Mergers

“…A timing of a precursor flare with the coincident gravitationalwave chirp which places the flare before coalescence would provide unambiguous evidence of a RSF. Such a coincident detection of would provide a powerful probe into the nuclear physics governing the properties of the NS matter near the crust-core interface (Tsang et al 2012;Neill et al 2021). Third generation GW detectors like the Einstein Telescope or Cosmic Explorer could push detection of solar mass mergers out to redshifts of 𝑧 ∼ 1 − 2 (Maggiore et al 2020;Abbott et al 2017a), and may be sensitive enough to directly detect the GW phase shift due to resonant excitation of stellar modes for nearby events without need for coincident EM detection of a RSF.…”

“…The quadrupole crust-core interface mode (𝑖-mode) of a NS has been identified as a likely candidate for triggering these RSFs (Tsang et al 2012). In a previous work (Neill et al 2021), we investigated how multi-messenger observation of a RSF and the GW signal from a binary merger could be used to constrain the properties of the neutron star crust, particularly near the crust-core boundary. These works did not explore the emission mechanisms and detectability of RSFs in detail, and just focused on what could be learned if any were detected.…”

“…For a description of the model used for the NS EOSs, see Neill et al (2021); Newton & Crocombe (2020) and references therein. Note that while in the former the EOS model is described in the context of fixing the maximum mass to 2.2 M , the same model can be used to target 3.0 M instead.…”

“…We would like to again stress that there is no evidence for a RSF occurring prior to GRB170817A. This SGRB was chosen due to it occurring at a relatively well determined distance, because said distance is low compared to other SGRBs, and because coincident GW detection is important with regards to RSFs (Tsang et al 2012;Neill et al 2021). The fact that no RSF appears to have occurred for this merger suggests that neither of the NSs involved had strong (> 10 13 G) surface magnetic fields.…”

“…In all, coincident EM-GW detections allow physics of the most extreme matter in the universe to be probed in unprecedented detail. In this paper we will investigate the emission and detectability of an EM counterpart that, if detected, can provide strong constraints on nuclear physics of neutron star matter (Neill et al 2021;Tsang et al 2012): Resonant Shattering Flares.…”