High-energy neutrino emission from the Type~IIn supernova SN~2017hcd

Abstract

Neutrino astronomy provides another window to exploring the Universe, exemplified by the detection of a megaelectronvolt neutrino burst from the core-collapse supernova (CCSN) SN~1987A (refs.~\citenum{hir+87,bio+87}). Commonly discussed theories suggest that some CCSNe could produce neutrinos with energies a thousand times more than those of SN~1987A \cite{tm18}, which has been probed with new-generation facilities \cite{abb+12,aar+15,abb+23}. The interaction of SN ejecta with a dense circumstellar medium (CSM) or a jet, launched in a CCSN, being choked in the stellar envelope of the progenitor or an outside CSM are both well-accepted scenarios for the high-energy neutrino production. Here we report the detection of a high-energy neutrino flare at a 3.9$σ$ significance from SN~2017hcd, made by our analysis of the public track-like neutrino data taken by the IceCube Neutrino Observatory \cite{IceCube17}. A Type IIn SN with optical emissions arising from the ejecta--CSM interaction, SN~2017hcd's neutrino flare lasted $\sim$1--2 month, with its central time $\sim$14-day prior to the SN's optical discovery time. Its estimated isotropic neutrino energy (all flavors) is approximately two orders of magnitude higher than the energy ($\sim 10^{50}$\,erg) carried in the SN's ejecta, too high to be explained with the ejecta--CSM scenario. Thus, a choked jet may be the source of the neutrino flare.

Figures (7)

• Figure 1: Neutrino flare determined at SN 2017hcd's position. The colored vertical lines are the individual neutrino events detected, with their heights being the weights (calculated with $\gamma = 3.5$; see section 'IceCube data analysis') and their colors being the reconstructed muon energies (indicated by the right-side color bar). The time durations of the flare, from the box and Gaussian time profile (marked by the 54-days cyan line and cyan dashed curve respectively) are shown. The whole X-axis time duration is the a priori window $T_{\rm win}$, within which the flare was searched. The central times of the durations precede the shock breakout time (marked by the gray dotted line) of the SN by $\sim$10 days; the latter was determined from the ATLAS o-band light curve (orange dots; see section 'Photometric data and light-curve analysis'). The estimated explosion time of the SN is marked by a blue dashed line.
• Figure 1: Optical images centered at the host galaxy of SN 2017hcd, MCG+05-05-002.Left panel: Pan-STARRs $i$-band image pan16 taken before the explosion of SN 2017hcd. Right panel: ATLAS $o$-band image taken at $\sim$54 days after the discovery time. In both panels, the red cross indicates the location of SN 2017hcd.
• Figure 2: Neutrino events detected at SN 2017hcd's position during the IceCube season IC86-II--VII. The weights and reconstructed muon energies of the events, the SN's estimated explosion time, and the neutrino flare's duration from the box time profile are respectively indicated as the same as those in Fig. \ref{['fig:lc']}. A clustering of high-weighted events at the SN explosion time is clearly visible.
• Figure 2: Left: parabolic fit (green dashed curve) to the ATLAS $o$-band light curve and the estimated shock-breakout time (marked by the gray dotted line) in the CSM. The orange dash-dotted line indicates the flux peak time of the light curve, and the blue dashed line indicates the estimated explosion time of SN 2017hcd. The observation time of the spectrum (shown in Extended Data Fig. \ref{['fig:spec']}) is marked by the red line. The determined two neutrino-flare time profiles (Fig. \ref{['fig:lc']}) are also shown for comparison. Right:extrabol fits to the multi-band data points of SN 2017hcd. The bands of the data points are marked at the right side of the fits.
• Figure 3: Neutrino TS map of a $4^\circ\times4^\circ$ region around SN 2017hcd (whose position is marked by a black star) during the best-fit flare period. The map was calculated using the box time profile, and the spectral index and time PDF were fixed at the best-fit values (see section 'IceCube data analysis').