Impact of binary interactions on the diffuse supernova neutrino background

Binary interactions, especially mass transfer and mergers, can strongly influence the evolution of massive stars and change their final properties and the occurrence of supernovae. Here, we investigate how binary interactions affect predictions of the diffuse flux of neutrinos. By performing stellar population syntheses including prescriptions for binary interactions, we show that the resulting detection rates of the diffuse supernova neutrino background is enhanced by 15%–20% compared to estimates without binary considerations. A source of significant uncertainty arises due to the presently sparse knowledge of the evolution of rapidly rotating carbon-oxygen cores, especially those created as a result of mergers near the white dwarf to core collapse boundary. The enhancement effect may be as small as a few percent if the effects of rotation in postmerger systems are neglected, or as large as 75% if trends are extrapolated. Our estimates serve to highlight that binary effects can be important.

Figure 1

The core mass increase due to rotational effects. The horizontal axis is the ZAMS mass. The vertical axis is the percentage of increase. Blue points are from the Limongi models [76], while the orange points are for our fiducial model [77]. The green line is the fitting to the Limongi models, while the red line is the fitting to our fiducial models. We adopt the combination of the two fits for our fiducial calculation.

Figure 2

Distributions of CO mass for our binary population synthesis compared to the case with no binary interactions (red solid). Three types of binary treatment with different postmerger evolution scenarios are shown: extending the study of Limongi et al. (black dot-dashed-dashed) [76], our fiducial model (green dot-dashed) [77], and a low version neglecting post-merger rotation (dashed blue). CE parameter is $\alpha \lambda =0.1$.

Figure 3

Same as Fig. 2, but showing the breakdown into different binary evolution channels. In the top panel we show nonmerge populations: single (light-blue dot-dot-dashed) and double systems (blue dot-dashed). In the bottom panel we show the merger channel, separately for the extending the study of Limongi et al. (black dot-dashed-dashed), our fiducial model (green dot-dashed), and a low version neglecting postmerger rotation (dashed blue). Total numbers in each channel are summarized in Table 1.

Figure 4

Cumulative bar charts of SN types, showing whether the progenitor merged or not for each. The horizontal axis shows the initial mass of progenitors. For merged progenitors, the horizontal axis shows the total initial mass of the binary.

Figure 5

Time-integrated neutrino spectral parameters: total neutrino energetic (top panel), mean energy (middle panel), and pinching parameter (bottom panel), shown separately for ${\nu }_e$ (red circles), ${\overline{\nu }}_e$ (blue squares), and ${\nu }_x$ (gray triangles). These are based on the 2D simulations of S16 augmented by simulations of a $9.6M_{\odot }$ star and a $8.8M_{\odot }$ ONeMg star. Note the axis change between the left and right, in logarithmic and linear, respectively. The dashed lines indicate our phenomenological fits through the simulations.

Figure 6

The core compactness (defined by $M=2.5M_{\odot }$) at moment of core-collapse, as a function of the CO core mass. The dashed lines separate the ONeMg regime and the Fe core regime in both compactness and CO mass planes.

Figure 7

The predicted DSNB flux of ${\overline{\nu }}_e$ for NH, for 6 different binary population synthesis models, compared with a single stellar evolution model. The binary population synthesis models include different treatments for the post-merger rapidly rotating stars and different CE modeling. We find that the minimal estimate, which neglects post-merger rotation effects (blue solid and dashed), yields a DSNB flux indistinguishable from a single stellar evolution model (red dot-dashed), while our fiducial scheme (green solid and dashed) and the extrapolated scheme (black solid and dashed) yield higher DSNB fluxes.

Figure 8

Reverse cumulative plot showing the fraction of progenitors with higher CO mass. Shown are the results for no binary treatment (solid red), the extrapolated scheme (black dot-dashed-dashed), our fiducial scheme (green dot-dashed), and a scheme neglecting post-merger rotation (dashed blue). Binary populations have higher fractions of CO cores massive enough to likely collapse to black holes ($M_{\mathrm{CO}}\gtrsim 10M_{\odot }$) than a no binary population. CE parameter is $\alpha \lambda =0.1$.