Gravitational wave triggered searches for high-energy neutrinos from binary neutron star mergers: Prospects for next generation detectors

The next generation gravitational wave (GW) detectors—Einstein Telescope (ET) and Cosmic Explorer (CE)—will have distance horizons up to $\mathcal{O}(10)\mathrm{Gpc}$ for detecting binary neutron star (BNS) mergers. This will make them ideal for triggering high-energy neutrino searches from BNS mergers at the next generation neutrino detectors, such as IceCube-Gen2. We calculate the distance limits as a function of the time window of neutrino analysis, up to which meaningful triggers from the GW detectors can be used to minimize backgrounds and collect a good sample of high-energy neutrino events at the neutrino detectors, using the sky localization capabilities of the GW detectors. We then discuss the prospects of the next generation detectors to work in synergy to facilitate coincident neutrino detections or to constrain the parameter space in the case of nondetection of neutrinos. We show that good localization of GW events, which can be achieved by multiple third generation GW detectors, is necessary to detect a GW-associated neutrino event or put a meaningful constraint ($\sim 3\sigma$ confidence level) on neutrino emission models. Such an analysis can also help constrain physical models and hence provide insights into neutrino production mechanisms in binary neutron star mergers.

Figure 1

(a) The left axis shows the size of the localization area in the sky for a single BNS merger event ($\mathrm{\Delta }\mathrm{\Omega }$) as a function of the luminosity distance $d_L$ for CE (dashed dark blue line), ET (dashed pink line), and $\mathrm{ET}+\mathrm{CE}$ (solid orange line). The right axis shows the BNS merger rate $R(z)$. The fiducial rate is shown as a solid teal line, and the area between the upper and the lower limits of $R(z=0)$ is shaded. (b) The fraction of sky area covered $f_{\mathrm{cov}}$ as a function of $d_L$ for CE (dot-dashed purple line), ET (dashed orange line), and $\mathrm{ET}+\mathrm{CE}$ (solid dark blue line) [see Eq. (4) for details]. The horizontal dotted lines show the threshold for the fraction of sky area covered $f_{\mathrm{th}}$ equal to ${10}^{-2}$ (red), ${10}^{-3}$ (green), and ${10}^{-4}$ (orange). The time duration assumed for the plot is $\delta t=1000\mathrm{s}$.

Figure 2

Density plot showing the distance upper limit for GW detectors ($d_{\mathrm{GW}}^{\mathrm{UL}}$) (see Eq. (5) for CE (left), ET (middle), and $\mathrm{ET}+\mathrm{CE}$ (right) on the $\delta t$—$f_{\mathrm{th}}$ plane.

Figure 3

Probability of neutrino detection ($q$) with the operation time $T_{\mathrm{op}}$ for a range of $f_{\nu }$ (top row) and $\delta t$ (bottom row) for the different GW detectors. The fiducial case for each panel is shown as a solid line. The $2\sigma$ and $3\sigma$ C.L.s are also shown with dashed lines. For each case, ${\mathcal{E}}_{\mathrm{GW}}=5\times {10}^{52}\mathrm{erg}$ and $\lambda ={10}^{-5}$. See the text for details on parameters.

Figure 4

The fraction of sky area covered $f_{\mathrm{th}}$ with operation time $T_{\mathrm{op}}$ for different values of triggered background events $N_{\mathrm{bkg}}^{\mathrm{trig}}$ at IceCube-Gen2.