Evidence for two neutrinos bursts from SN1987A

The SN1987A in the Giant Magellanic Cloud was an amazing and extraordinary event because it was detected in real time for different neutrinos experiments ($\nu$s) around the world. Approximate $\sim25$ events were observed in three different experiments: Kamiokande II (KII) $\sim 12$, Irvine-Michigan-Brookhaven (IMB) $\sim 8$ e Baksan $\sim 5$, plus a contrived burst at Mont Blanc (Liquid Scintillator Detector - LSD) later dismissed because of energetic requirements (Aglietta et al. 1988). The neutrinos have an important play role into the neutron star newborn: at the moment when the supernova explodes the compact object remnant is freezing by neutrinos ($\sim99\%$ energy is lost in the few seconds of the explosion). The work is motivated by neutrinos' event in relation arrival times where there is a temporal gap between set of events ($\sim6\mbox{s}$). The first part of dataset came from the ordinary mechanism of freezing and the second part suggests different mechanism of neutrinos production. We tested two models of cooling for neutrinos from SN1987A: 1st an exponential cooling is an ordinary model of cooling and 2nd a two-step temperature model that it considers two bursts separated with temporal gap. Our analysis was done with Bayesian tools ({\it Bayesian Information Criterion} - BIC) The result showed strong evidence in favor of a two-step model against one single exponential cooling ($\ln\mbox{B}_{ij} > 5.0$), and suggests the existence of two neutrino bursts at the moment the neutron star was born.