1112.3462 (Rodrigo Negreiros et al.)

Cooling of young neutron stars in GRB associated to Supernova    [PDF]

Rodrigo Negreiros, Remo Ruffini, Carlo Luciano Bianco, Jorge A. Rueda

Recent observations of the late ($t=10^8$--$10^9$ s) emission of Supernovae associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures $10^7$--$10^8$ K. Similar features have been also observed in the two Type Ic SN 2002ap and SN 1994I, not associated to GRBs. We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star (NS) just formed in the SN event, here defined as a neo-NS. We discuss the thermal evolution of neo-NS in the age regime that spans from $\sim 1$ minute (just after the proto-NS phase) up to <10-100 yr. We examine the key factor governing the neo-NS cooling emphasizing on the neutrino emission. A phenomenological heating source and new boundary conditions are introduced to mimic the high temperature of the atmosphere for young NSs. We thus match the neo-NS luminosity to the late X-ray emission of the GRB-SN events: URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. By calibrating our additional heating source at early times to $\sim 10^{12}$--$10^{15}$ erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of neo-NSs with the prolonged ($t=10^{8}$--$10^{9}$ s) X-ray emission observed in GRB-SN. It seems appropriate to revise the boundary conditions usually used in the thermal cooling theory of NSs, in order to match the proper conditions of the atmosphere at young ages. Additional heating processes not yet studied within this context, e.g. e+e- pair creation by overcritical fields and nuclear fusion and fission energy release, might also take place under such conditions and deserve further analysis. The observation of GRB-SN has evidenced the possibility of witnessing the thermal evolution of neo-NSs. A new campaign of dedicated observations of GRB-SN and isolated Type Ic SN is recommended.

View original: http://arxiv.org/abs/1112.3462