MUSE Integral Field Observations of the Oxygen-rich SNR 1E 0102.2-7219

TL;DR

This study uses advanced integral field spectroscopy to uncover new elements and dynamics in the oxygen-rich supernova remnant 1E 0102.2-7219, challenging previous progenitor models and revealing complex shock and nucleosynthesis features.

Contribution

It presents the first detection of sulfur-rich ejecta and fast-moving hydrogen in the remnant, providing new insights into its explosion mechanism and progenitor star.

Findings

Detection of sulfur-rich ejecta

Discovery of fast-moving hydrogen knots

Observation of shock-related [Fe xiv] and [Fe xi] emission lines

Abstract

We have observed the oxygen-rich SNR 1E 0102.2-7219 with the integral field spectrograph WiFeS at Siding Spring Observatory and discovered sulfur-rich ejecta for the first time. Follow-up deep DDT observations with MUSE on the VLT (8100 s on source) have led to the additional discovery of fast- moving hydrogen as well as argon-rich and chlorine-rich material. The detection of fast-moving hydrogen knots challenges the interpretation that the progenitor of 1E 0102 was a compact core of a Wolf-Rayet star that had shed its entire envelope. In addition to the detection of hydrogen and the products of oxygen-burning, this unprecedented sharp (0.2" spaxel size at ~0.7" seeing) and deep MUSE view of an oxygen-rich SNR in the Magellanic Clouds reveals further exciting discoveries, including [Fe xiv]{\lambda}5303 and [Fe xi]{\lambda}7892 emission, which we associate with the forward shock. We present this exciting data set and discuss some of its implications for the explosion mechanism and nucleosynthesis of the associated supernova.

Figures

Full text

††volume: 331††journal: SN 1987A, 30 years later – Cosmic Rays and Nuclei from Supernovae and their aftermaths††editors: M. Renaud, A. Marcowith, G. Dubner, A. Ray & A. Bykov, eds.

1 Introduction

1E 0102.2-7219 (1E 0102 for short) belongs to the class of oxygen-rich young supernova remnants (O-rich YSNRs) showing remarkably little-to-no hydrogen emission. The prominent oxygen forbidden-line emission observed in the filaments and knots (see Figs. 1, 2) is understood to arise from shocked ejecta from a core-collapse supernova that had been stripped of (most of) its hydrogen envelope prior to explosion. Unlike most SNRs, where the optical emission comes from interstellar medium ionized by the forward shock, O-rich YSNRs are special in that one can study the actual ejecta composition of the supernova, providing unique and direct insights into explosion mechanisms and nucleosynthesis conditions in core-collapse supernovae. Only a handful of such O-rich YSNRs are known: the best studied examples include Cas A in our Galaxy and 1E 0102 in the Small Magellanic Cloud (SMC). Since the discovery of the high-velocity oxygen-rich supernova ejecta in 1E 0102 ([Dopita et al. 1981]), subsequent searches (including HST FOS spectroscopy and WFC3 imaging) for the expected products of oxygen burning, in particular sulfur, have returned negative results (e.g., [Lasker & Golimowski 1991, Blair et al. 2000]). These searches have only detected carbon, oxygen, neon, and magnesium, but no products of oxygen-burning, i.e., no sulfur, silicon, calcium, or argon. The angular size of 1E 0102 (50*′′* in diameter) and the large Doppler shifts associated with its fast-moving ejecta ($v\gtrsim 1000\,\mathrm{km\,s}^{-1}$) have been strong limitations for previous long-slit spectroscopic and narrow-band imaging searches, which have either failed to map locations of interest and/or were blind to fast-moving ejecta altogether.

2 WiFeS observations

In our observations (P.I.: Seitenzahl) on the nights of Aug. 7 and Aug. 8, 2016 with the WiFeS Integral Field Spectrograph on the 2.3 m telescope at Siding Springs Observatory, we have detected fast-moving (mostly, but not exclusively blue-shifted) [S ii]$\lambda\lambda 6716,6731$ emission (see Fig. 1). These data represent the first detection in the optical of the products of oxygen-burning in the ejecta of 1E 0102. The first set of observations were performed with the R7000 and B7000 gratings in place and constituted a co-added $2\times 1800\,\mathrm{s}$ science observation block for each of the two pointings that make up the mosaic, with a 900 s dark sky frame before and after. We re-visited the same two fields of the target for an additional $2\times 1800\,\mathrm{s}$ per science field on the nights of Oct. 28 and Oct. 29, 2016, this time with the B3000 in the blue arm to include [O ii]$\lambda\lambda$3726,3729 and [Ne iii]$\lambda\lambda$3869,3967 (see Fig. 2). All data were reduced and flux-calibrated with the PyWiFeS pipeline ([Childress et al. 2014]).

3 MUSE observations

We observed 1E 0102 with the Multi-Unit Spectroscopic Explorer (MUSE) in Service Mode at the Very Large Telescope on the night of October 7, 2016 via Director’s Discretionary Time (DDT) program 297.D-5058 (P.I.: F.P.A. Vogt). We obtained a total of $9\times 900\,\mathrm{s}$ exposures on-source, with appropriate 180 s dark sky exposures away from the SMC in between the science exposures. The data frames were individually reduced and then combined into a single data cube with the ESO Reflex workflow ([Freudling et al. 2013]), for further details see [Vogt et al. 2017b]. Compared to the 1*′′* by 1*′′* spaxel size and ${\sim}$1.5*′′* seeing of the WiFeS cube, the 0.2*′′* by 0.2*′′* spaxel size and ${\sim}$0.7*′′* seeing of the MUSE cube offers a much sharper view of 1E 0102 (see Fig. 3). In addition to gaining in spatial resolution, the MUSE observations have increased the sensitivity by a factor of approximately 100, improving from the WiFeS noise level of a few times $10^{-18}\,\mathrm{erg}\mathrm{s}^{-1}\mathrm{cm}^{-2}\mathrm{\AA}^{-1}\mathrm{spaxel}^{-1}$ to a noise level of a few times $10^{-20}\,\mathrm{erg}\mathrm{s}^{-1}\mathrm{cm}^{-2}\mathrm{\AA}^{-1}\mathrm{spaxel}^{-1}$.

4 Summary

In this contribution, we have presented optical integral field spectroscopy observations of 1E 0102.2-7219 performed with the WiFeS and MUSE instruments. The combined data cubes extend from $3500\,\mathrm{\AA}$ to $9350\,\mathrm{\AA}$. In addition to mapping out the (previously known) O- and Ne-rich ejecta in unprecedented detail, we have discovered fast-moving [S ii], [S iii], [Ar iii], H$\alpha$, H$\beta$, and possibly [Cl ii], which we attribute to be components of the supernova ejecta. S, Ar, and Cl are main nucleosynthesis products of O-burning, which we detect here as ejecta in the optical in 1E 0102 for the first time. The discovery of Balmer line emission in the ejecta indicates that the progenitor star must not have been entirely stripped of its hydrogen envelope when it exploded. We have also discovered high ionization coronal lines of Fe ([Fe x], [Fe xi], and [Fe xiv]) and the photoionization precursor emission, which can be used to derive the forward shock parameters (see [Vogt et al. 2017b]).

5 Acknowledgements

This research has made use of brutus, a Python module to process data cubes from integral field spectrographs hosted at http://fpavogt.github.io/brutus/. For this analysis, brutus relied on statsmodel ([Seabold & Perktold 2010]), matplotlib ([Hunter 2007]), astropy, a community-developed core Python package for Astronomy ([Astropy Collaboration 2013]), aplpy, an open-source plotting package for Python hosted at http://aplpy.github.com, and montage, funded by the National Science Foundation under Grant Number ACI-1440620 and previously funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. This research has also made use of the aladin interactive sky atlas ([Bonnarel et al. 2000]), of saoimage ds9 ([Joye & Mandel 2003]) developed by Smithsonian Astrophysical Observatory, of NASA’s Astrophysics Data System, and of the NASA/IPAC Extragalactic Database (NED; [Helou et al. 1991]), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. IRS was supported in part by the Australian Research Council Laureate Grant FL0992131 and the Future Fellowship Grant FT160100028. AJR acknowledges funding through the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) through project number CE110001020. PG thanks the Stromlo Distinguished Visitor Programme. FPAV and IRS thank the CAASTRO AI travel grant for generous support. Based in part on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 297.D-5058[A] and the ANU 2.3 m telescope at Siding Spring Observatory.