The compact object and innermost ejecta of SN 1987A

TL;DR

This study uses JWST observations to analyze the innermost ejecta of SN 1987A, confirming the presence of a compact object and characterizing its properties, including potential neutron star kick velocity and dust effects.

Contribution

The paper provides detailed spectral analysis of SN 1987A's ejecta using high-resolution JWST data, identifying new emission lines and modeling the ionization sources and dust influence.

Findings

Confirmed narrow emission lines from the central region.

Estimated neutron star kick velocity of approximately 510 km/s.

Demonstrated dust scattering and absorption effects on observed spectra.

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/MRS 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; [Ar VI] 4.5292 $\mu$m, [Ar II] 6.9853 $\mu$m, [S IV] 10.5105 $\mu$m, and [S III] 18.7130 $\mu$m, and also identify similar components in [Ca V] 4.1585 $\mu$m, [Cl II] 14.3678 $\mu$m, and possibly [Fe II] 1.6440 $\mu$m. These lines are blueshifted by $\sim$ -250 km/s, while the emission region is spatially unresolved and located southeast of the center. The offset and blueshift could imply a kick velocity of $510 \pm 55$ km/s for the neutron star. We also identify [Ca IV] 3.2068 $\mu$m near the center, but it is displaced to the north and has a redshift of $\sim 700$ km/s. We find that scattering by dust in the ejecta with a typical grain size $\sim 0.3\ \mu$m can explain the [Ca IV] properties and the absence of other narrow lines at shorter wavelengths, while dust absorption is important at $\lambda \gtrsim 8\ \mu$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.