ISO/SWS observations of SN 1987A. II. A refined upper limit on the mass of ⁴⁴Ti in the ejecta of SN 1987A

Abstract

ISO/SWS observations of SN 1987A on day 3425 show no emission in [Fe I] 24.05 mum and [Fe II] 25.99 mum down to the limits ~ 0.39 Jy and ~ 0.64 Jy, respectively. Assuming a homogeneous distribution of ⁴⁴Ti inside 2000 km s^-1 and negligible dust cooling, we have made time dependent theoretical models to estimate an upper limit on the mass of ejected ⁴⁴Ti. Assessing various uncertainties of the model, and checking the late optical emission it predicts, we obtain an upper limit of =~ 1.1EE -4 M_sun. This is lower than in our previous estimate using other ISO data, and we compare our new result with other models for the late emission, as well as with expected yields from explosion models. We also show that steady-state models for the optical emission are likely to overestimate the mass of ejected ⁴⁴Ti. The low limit we find for the mass of ejected ⁴⁴Ti could be higher if dust cooling is important. A direct check on this is provided by the gamma-ray emission at 1.157 Mev as a result of the radioactive decay of ⁴⁴Ti. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the UK) and with the participation of ISAS and NASA.