2019ApJ...874...14X

We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E 0102.2-7219 in X-rays using Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectrometer observations from 1999 to 2016. We estimate an expansion rate of 0.025% ± 0.006% yr^–1 and a blast wave velocity of (1.61±0.37)×10³kms^–1. Assuming partial electron-ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a post-shock electron temperature of 0.84 ± 0.20 keV, which is consistent with the estimate of 0.68 ± 0.05 keV based on the X-ray spectral analysis. We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one-dimensional models for a range of ejecta masses (2–6M_☉) to constrain the explosion energy, age, circumstellar density, swept-up mass, and unshocked-ejecta mass. We find acceptable solutions for a constant-density ambient medium and for an r^–2 power-law profile (appropriate for a constant progenitor stellar wind). For the constant-density case, we find an age of ∼1700 yr, explosion energies (0.87-2.61) x 10⁵¹ erg, ambient densities 0.85-2.54 amu cm^–3, swept-up masses 22–66M_☉, and unshocked-ejecta masses 0.05–0.16M_☉. For the power-law density profile, we find an age of ∼2600 yr, explosion energies (0.34-1.02) x 10⁵¹ erg, densities 0.22–0.66amucm^–3 at the blast wave, swept-up masses 17–52M_☉, and unshocked-ejecta masses 0.06–0.18M_☉. Assuming that the true explosion energy was (0.5-1.5) x 10⁵¹ erg, ejecta masses 2–3.5M_☉ are favored for the constant-density case and 3–6M_☉ for the power-law case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass 15.0–40.0M_☉, offering a possible explanation for the lack of Fe emission observed in X-rays.