Detecting neutrinos from black hole-neutron star mergers

While it is well known that neutrinos are emitted from standard core collapse protoneutron star supernovae, less attention has been focused on neutrinos from accretion disks. These disks occur in some supernovae (i.e. collapsars) as well as in compact object mergers, and they emit neutrinos with similar properties to those from protoneutron star supernovae. These disks and their neutrinos play an important role in our understanding of gamma ray bursts as well as the nucleosynthesis they produce. We study a disk that forms in the merger of a black hole and a neutron star and examine the neutrino fluxes, luminosities and neutrino surfaces for the disk. We also estimate the number of events that would be registered in current and proposed supernova neutrino detectors if such an event were to occur in the Galaxy.

Figure 1

Transversal cut of neutrino surfaces at $\varphi =20°$. The solid line corresponds to electron neutrino surface whereas the dashed and dotted lines correspond to electron antineutrino and tau neutrino, respectively. The circle around $r=0$ represents the BH boundary.

Figure 2

Temperature profile of the electron antineutrino surface seen from the $z$ axis. The black frame, $x=[-70,75]$, $y=[-75,70]\mathrm{km}$, encloses the antineutrino surface. The temperature scale (on the right) goes from blue $T=2\mathrm{MeV}$, to red $T\sim 14\mathrm{MeV}$. The black circular area represents the black hole boundary, $r=2r_s$.

Figure 3

Electron antineutrino surface seen at some inclination angle (see the $x$, $y$, $z$ axis on the lower left corner). The height corresponds to $h_{\nu }$ as in Eq. (2). The color scale corresponds to the neutrino temperatures, also shown in Fig. 2. The black area in the center represents the boundary with the BH, $r=2r_s$.

Figure 4

Diagram showing the effects of the BH gravitational field on neutrino trajectories. The black dot represents the BH, $r_{\nu }$ is the emission point on the neutrino surface, which we have sketched with the horizontal line, $b$ is the impact parameter of the trajectory (thick line) and $\theta$ is the angle measured by an observer at $z_{\mathrm{eva}}$. According to this observer the emission point would be located at $r_{\nu }^{*}$.