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

## TL;DR

This study measures the expansion of the supernova remnant 1E 0102.2-7219 in X-rays, constraining its age, explosion energy, and ejecta mass through observational data and modeling, providing insights into its explosion dynamics and progenitor characteristics.

## Contribution

First detailed measurement of the remnant's expansion rate and velocity using Chandra data, combined with modeling to constrain explosion parameters and ejecta mass.

## Key findings

- Expansion rate of 0.025% per year
- Estimated blast-wave velocity of 1.61×10^3 km/s
- Ejecta mass estimates consistent with core-collapse supernovae

## 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 Spectromete(ACIS) observations from 1999-2016. We estimate an expansion rate of 0.025%\pm0.006%yr^{-1} and a blast-wave velocity of 1.61\pm0.37\times10^3 km s^{-1}. Assuming partial electron-ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a postshock electron temperature of 0.84\pm0.20 keV which is consistent with the estimate of 0.68\pm0.05 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 \msol) 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 \sim 1700 yr, explosion energies 0.87-2.61\times10^{51} erg, ambient densities 0.85-2.54 amu cm^{-3}, swept-up masses 22-66 \msol, and unshocked-ejecta masses 0.05-0.16 \msol. For the power-law density profile, we find an age of \sim 2600 yr, explosion energies 0.34-1.02\times10^{51} erg, densities 0.22-0.66 amu cm^{-3} at the blast wave, swept-up masses 17-52 \msol, and unshocked-ejecta masses 0.06-0.18 \msol. Assuming the true explosion energy was 0.5-1.5\times10^{51} erg, ejecta masses 2-3.5 \msol are favored for the constant density case and 3-6 \msol 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 \msol, offering a possible explanation for the lack of Fe emission observed in X-rays.