The Expansion of the Forward Shock of 1E 0102.2-7219 in X-Rays

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) x 10(3) km s(-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 (2-6 M-circle dot) 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 similar to 1700 yr, explosion energies (0.87-2.61) x 10(51) erg, ambient densities 0.85-2.54 amu cm(3), swept-up masses 22-66 M-circle dot, and unshocked-ejecta masses 0.05-0.16 M-circle dot. For the power-law density profile, we find an age of similar to 2600 yr, explosion energies (0.34-1.02) x 10(51) erg, densities 0.22-0.66 amu cm(-3) at the blast wave, swept-up masses 17-52 M-circle dot, and unshocked-ejecta masses 0.06-0.18 M-circle dot. Assuming that the true explosion energy was (0.5-1.5) x 10(51) erg, ejecta masses 2-3.5 M-circle dot are favored for the constant-density case and 3-6 M-circle dot for the powerlaw case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass 15.0-40.0 M-circle dot, offering a possible explanation for the lack of Fe emission observed in X-rays.