The supernova remnant population of the Small Magellanic Cloud

Pierre Maggi,Jean Ballet,Miroslav D Filipović,Milorad Stupar,Chandreyee Maitra,Manami Sasaki,Branislav Vukotić,Patrick Kavanagh,Frank Haberl

doi:10.1051/0004-6361/201936583

Abstract

Aims.We present a comprehensive study on the supernova remnant (SNR) population of the Small Magellanic Cloud (SMC). We measured multiwavelength properties of the SMC SNRs and compare them to those of the Large Magellanic Cloud (LMC) population.Methods.This study combines the large dataset ofXMM-Newtonobservations of the SMC, archival and recent radio continuum observations, an optical line emission survey, and new optical spectroscopic observations. We were therefore able to build a complete and clean sample of 19 confirmed and four candidate SNRs. The homogeneous X-ray spectral analysis allowed us to search for SN ejecta and Fe K line emission, and to measure interstellar medium abundances. We estimated the ratio of core-collapse to type Ia supernova rates of the SMC based on the X-ray properties and the local stellar environment of each SNR.Results.After the removal of unconfirmed or misclassified objects, and the addition of two newly confirmed SNRs based on multi-wavelength features, we present a final list of 21 confirmed SNRs and two candidates. While no Fe K line is detected even for the brightest and youngest SNR, we find X-ray evidence of SN ejecta in 11 SNRs. We estimate a fraction of 0.62–0.92 core-collapse supernova for every supernova (90% confidence interval), higher than in the LMC. The difference can be ascribed to the absence of the enhanced star-formation episode in the SMC, which occurred in the LMC 0.5–1.5 Gyr ago. The hot-gas abundances of O, Ne, Mg, and Fe are 0.1–0.2 times solar. Their ratios, with respect to SMC stellar abundances, reflect the effects of dust depletion and partial dust destruction in SNR shocks. We find evidence that the ambient medium probed by SMC SNRs is less disturbed and less dense on average than in the LMC, consistent with the different morphologies of the two galaxies.

Highlights

A fraction of stars end their lives in powerful supernova (SN) explosions (e.g. Alsabti & Murdin 2017, and references therein)
We note that our derived abundance ratios [O/Fe] or [α/Fe] are well consistent with other studies, indicating that we have efficiently vetoed contamination by the more frequent CC supernova remnant (SNR) ejecta, as we have shown for the Large Magellanic Cloud (LMC) interstellar medium (ISM) as well (Hughes et al 1998, MHK16)
– By combining deep, large scale XMM-Newton and radio surveys of the Small Magellanic Cloud (SMC), we presented a clean list of 19 bona-fide SNRs and identified 4 more candidates

Summary

Introduction

A fraction of stars end their lives in powerful supernova (SN) explosions (e.g. Alsabti & Murdin 2017, and references therein). X-ray spectra We follow the spectral analysis method described extensively in MHK16: we simultaneously fit source and background spectra (hereafter SRC and BG), where the latter is explicitly modelled rather than subtracted This is critical for the analysis of faint extended sources such as SNRs in the SMC. We correct the event lists for vignetting with the SAS task evigweight prior to extraction This accounts for the energy-dependent effective area variation across the extents of SNRs and background regions. Spectra extracted from FWC data at the same detector positions as the SRC and BG regions are used to fit the instrumental background model It comprises electronic noise and particleinduced background, as described in Kuntz & Snowden (2008); Sturm (2012); and MHK16. SMC) This is likely due to variations of the X-ray background or diffuse emission on small angular scales

Results and discussion

General properties

Three-dimensional spatial distribution

Summary We summarise below our work and findings: