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

Abstract

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 ) × 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 ☉ ) 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) × 10 51 erg, ambient densities 0.85–2.54 amu cm −3 , swept-up masses 22 – 66 M ☉ , and unshocked-ejecta masses 0.05 – 0.16 M ☉ . For the power-law density profile, we find an age of ∼2600 yr, explosion energies (0.34–1.02) × 10 51 erg, densities 0.22 – 0.66 amu cm − 3 at the blast wave, swept-up masses 17 – 52 M ☉ , and unshocked-ejecta masses 0.06 – 0.18 M ☉ . Assuming that the true explosion energy was (0.5–1.5) × 10 51 erg, ejecta masses 2 – 3.5 M ☉ are favored for the constant-density case and 3 – 6 M ☉ 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 – 40.0 M ☉ , offering a possible explanation for the lack of Fe emission observed in X-rays.