Hints of a second explosion (a quark nova) in Cassiopeia A Supernova
  We show that the explosive transition of the neutron star (NS) to a quark star (QS) (a Quark Nova) in Cassiopeia A (Cas A) a few days following the SN proper can account for several of the puzzling kinematic and nucleosynthetic features observed. The observed decoupling between Fe and 44Ti and the lack of Fe emission within 44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by the relativistic QN neutrons. Our model predicts the 44Ti to be more prominent to the NW of the central compact object (CCO) than in the SE and little of it along the NE-SW jets, in agreement with NuStar observations. Other intriguing features of Cas A such as the lack of a pulsar wind nebula (PWN) and the reported a few percent drop of the CCO temperature over a period of 10 years are also addressed. 
Rachid Ouyed, Denis Leahy, Nico Koning (Department of Physics and   Astronomy, University of Calgary, Canada)
astro-ph.HE