Tools for dissecting supernova remnants observed with chandra: Methods and application to the galactic remnant W49B

Abstract

We introduce methods to quantify the X-ray morphologies of supernova remnants (SNRs) observed with the Chandra X-ray Telescope. These include a power-ratio technique to measure morphological asymmetries, correlation-length analysis to probe chemical segregation and distribution, and wavelet-transform analysis to quantify the X-ray substructure. We demonstrate the utility and accuracy of these techniques on relevant synthetic data. Additionally, we show the methods' capabilities by applying them to the 55 ks Chandra Advanced CCD Imaging Spectrometer observation of the galactic SNR W49B. We analyze the images of prominent emission lines in W49B and use the results to discern physical properties. We find that the iron morphology is very distinct from the other elements: it is statistically more asymmetric, more segregated, and has 25% larger emitting substructures than the lighter ions. Comparatively, the silicon, sulfur, argon, and calcium are well mixed, more isotropic, and have smaller, equally sized emitting substructures. Based on fits of XMM-Newton spectra in regions identified as iron rich and iron poor, we determine that the iron in W49B must have been anisotropically ejected. We measure the abundance ratios in many regions, and we find that large, local variations are persistent throughout the remnant. We compare the mean, global abundance ratios to those predicted by spherical and bipolar core-collapse explosions; the results are consistent with a bipolar origin from a ∼25 M⊙ progenitor. We calculate the filling factor of iron from the volume of its emitting substructures, enabling more precise mass estimates than previous studies. Overall, this work is a first step toward rigorously describing the physical properties of SNRs for comparison within and between sources. © 2009. The American Astronomical Society. All rights reserved.