Kinematics, structure and abundances of supernova remnant 0540-69.3

Abstract

The structure, elemental abundances, physical conditions of the LMC supernova remnant (SNR) 0540-69.3 and its surroundings were investigated using [O III] imaging and spectroscopy. Several new spectral lines are identified, both in central filaments and in interstellar clouds shocked by the supernova blast wave. The central lines are redshifted by $440\pm 80$ km s${}^{-1}$ with respect to the LMC, and the [O III] emission displays a symmetry axis of ring-like structures which could indicate that the pulsar shares the same general redshift as the central supernova ejecta. [O II], [S II], [Ar III] and H$\beta$ have more compact structures than [O III], and possibly [Ne III]. The average [O III] temperature is $23500\pm 1800$ K, and the electron density from [S II] is typically $10^3$ cm${}^{-3}$. By mass, the relative elemental abundances of the central shocked ejecta are $\mathrm{O}:\mathrm{Ne}:\mathrm{S}:\mathrm{Ar}\approx 1:0.07:0.10:0.02$, consistent with explosion models of $13-20$ solar mass progenitors, and similar to that of SN 1987A, as is also the mixing of hydrogen and helium into the center. [O III] is also seen in freely coasting ejecta outside the pulsar-wind nebula out to well above $2000$ km s${}^{-1}$. From this a pulsar age of $\approx 1200$ years is estimated. Four filaments of shocked interstellar medium with a wide range in degree of ionization of iron are identified. One was observed in X-rays, and another has a redshift of $85\pm 30$ km~s${}^{-1}$ relative to LMC. From this the electron density of the [O III]-emitting gas is estimated to be $10^3$ cm${}^{-3}$. The line of the most highly ionized ion, [Fe XIV] $\lambda$5303, likely comes from an evaporation zone in connection with the radiatively cooled gas emitting, e.g., [O III].

Submitted to Astronomy and Astrophysics Aug. 2, 2021. 30 pages, 26 figures and 5 tables

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