The Compact Object and Innermost Ejecta of SN 1987A

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 μm, [Ar ii] 6.9853 μm, [S iv] 10.5105 μm, and [S iii] 18.7130 μm), and also identify similar components in [Ca v] 4.1585 μm, [Cl ii] 14.3678 μm, and possibly [Fe ii] 1.6440 μm. 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 μm 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 μm can explain the [Ca iv] properties and the absence of other narrow lines at shorter wavelengths, while dust absorption is important at λ ≳ 8 μm. 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.