A Possible Supernova Remnant high above the Galactic Disk

TL;DR

This study analyzes Suzaku X-ray observations of a bright arc in the sky, proposing it as the edge of a supernova remnant located above the Galactic disk, contributing to understanding halo gas heating.

Contribution

It provides the first detailed modeling of an extraplanar supernova remnant as the origin of a high-altitude X-ray arc, supporting the role of supernovae in halo gas heating.

Findings

The arc is consistent with a ~100,000-year-old SNR 1-2 kpc above the disk.

Metallicity of the X-ray emitting gas is about 1/3 solar.

The model explains the size and brightness of the arc reasonably well.

Abstract

We present the analysis of three Suzaku observations of a bright arc in the ROSAT All-Sky Survey 1/4 keV maps at $l \approx 247\degr$, $b \approx -64\degr$. In particular, we have tested the hypothesis that the arc is the edge of a bubble blown by an extraplanar supernova. One pointing direction is near the brightest part of the arc, one is toward the interior of the hypothesized bubble, and one is toward the bubble exterior. We fit spectral models generated from 1-D hydrodynamical simulations of extraplanar supernova remnants (SNRs) to the spectra. The spectra and the size of the arc ($\mathrm{radius} \approx 5\degr$) are reasonably well explained by a model in which the arc is the bright edge of a $\sim$100,000-yr old SNR located $\sim$1--2 kpc above the disk. The agreement between the model and the observations can be improved if the metallicity of the X-ray--emitting gas is $\sim$1/3 solar, which is plausible, as the dust which sequesters some metals is unlikely to have been destroyed in the lifetime of the SNR. The width of the arc is larger than that predicted by our SNR model; this discrepancy is also seen with the Vela SNR, and may be due to the 1-D nature of our simulations. If the arc is indeed the edge of an extraplanar SNR, this work supports the idea that extraplanar supernovae contribute to the heating of the $\sim$million-degree gas in the halo.