The Compact Object and Innermost Ejecta of SN 1987A

Abstract The first JWST observations of SN 1987A provided clear evidence that a compact object is ionizing the innermost ejecta. Here, we analyze a second epoch of JWST NIRSpec and MIRI/Medium-Resolution Spectrometer observations to better characterize the properties of this region, aided by a higher spectral resolving power for the new NIRSpec data. We confirm the presence of the previously identified narrow lines from the central region, i.e., (Ar vi 4.5292 μ m, Ar ii 6.9853 μ m, S iv 10.5105 μ m, and S iii 18.7130 μ m), and also identify similar components in Ca v 4.1585 μ m, Cl ii 14.3678 μ m, and possibly Fe ii 1.6440 μ m. These lines are blueshifted by ∼−250 km s −1 , while the emission region is spatially unresolved and located southeast of the center. The offset and blueshift could imply a kick velocity of 510 ± 55 km s −1 for the neutron star. We also identify Ca iv 3.2068 μ m near the center, but it is displaced to the north and has a redshift of ∼700 km s −1 . We find that scattering by dust in the ejecta with a typical grain size ∼0.3 μ m can explain the Ca iv properties and the absence of other narrow lines at shorter wavelengths, while dust absorption is important at λ ≳ 8 μ m. Photoionization models for a pulsar wind nebula and a cooling neutron star are both compatible with the observations, with the exception of the Fe ii feature. The two models primarily differ at short wavelengths, where new lines are expected to emerge over time as the optical depth of dust in the expanding ejecta decreases.