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The Population of X-Ray Supernova Remnants in the Large Magellanic Cloud

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The Population of X-Ray Supernova Remnants in the Large Magellanic Cloud A&A 585, A162 (2016) Astronomy DOI: 10.1051/0004-6361/201526932 & © ESO 2016 Astrophysics The population of X-ray supernova remnants in the Large Magellanic Cloud P. Maggi1,2, F. Haberl1,P.J.Kavanagh3, M. Sasaki3,L.M.Bozzetto4, M. D. Filipovic´4, G. Vasilopoulos1, W. Pietsch1,S.D.Points5, Y.-H. Chu6,J.Dickel7,M.Ehle8, R. Williams9, and J. Greiner1 1 Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstr., 85741 Garching, Germany e-mail: [email protected] 2 Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France 3 Institut für Astronomie und Astrophysik Tübingen, Universität Tübingen, Sand 1, 72076 Tübingen, Germany 4 University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia 5 Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Cassilla 603 La Serena, Chile 6 Institute of Astronomy and Astrophysics, Academia Sinica, No.1, Sec. 4, Roosevelt Rd, 10617 Taipei, Taiwan, Republic of China 7 Physics and Astronomy Department, University of New Mexico, MSC 07-4220, Albuquerque, NM 87131, USA 8 XMM-Newton Science Operations Centre, ESA/ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain 9 Columbus State University Coca-Cola Space Science Center, 701 Front Avenue, Colombus, GA 31901, USA Received 10 July 2015 / Accepted 28 September 2015 ABSTRACT Aims. We present a comprehensive X-ray study of the population of supernova remnants (SNRs) in the Large Magellanic Cloud (LMC). Using primarily XMM-Newton observations, we conduct a systematic spectral analysis of LMC SNRs to gain new insight into their evolution and the interplay with their host galaxy. Methods. We combined all the archival XMM-Newton observations of the LMC with those of our Very Large Programme LMC survey. We produced X-ray images and spectra of 51 SNRs, out of a list of 59 objects compiled from the literature and augmented with newly found objects. Using a careful modelling of the background, we consistently analysed all the X-ray spectra and measure temperatures, luminosities, and chemical compositions. The locations of SNRs are compared to the distributions of stars, cold gas, and warm gas in the LMC, and we investigated the connection between the SNRs and their local environment, characterised by various star formation histories. We tentatively typed all LMC SNRs, in order to constrain the ratio of core-collapse to type Ia SN rates in the LMC. We also compared the column densities derived from X-ray spectra to H i maps, thus probing the three-dimensional structure of the LMC. Results. This work provides the first homogeneous catalogue of the X-ray spectral properties of SNRs in the LMC. It offers a complete census of LMC remnants whose X-ray emission exhibits Fe K lines (13% of the sample), or reveals the contribution from hot supernova ejecta (39%), which both give clues to the progenitor types. The abundances of O, Ne, Mg, Si, and Fe in the hot phase of the LMC interstellar medium are found to be between 0.2 and 0.5 times the solar values with a lower abundance ratio [α/Fe] than = +0.11 in the Milky Way. The current ratio of core-collapse to type Ia SN rates in the LMC is constrained to NCC/NIa 1.35(−0.24), which is lower than in local SN surveys and galaxy clusters. Our comparison of the X-ray luminosity functions of SNRs in Local Group galaxies (LMC, SMC, M31, and M33) reveals an intriguing excess of bright objects in the LMC. Finally, we confirm that 30 Doradus and the LMC Bar are offset from the main disc of the LMC to the far and near sides, respectively. Key words. ISM: supernova remnants – Magellanic Clouds – ISM: abundances – supernovae: general – stars: formation – X-rays: ISM 1. Introduction may also explode as type Ia SNe (Sim et al. 2010; van Kerkwijk et al. 2010; Woosley & Kasen 2011). The thermonuclear burn- Supernova remnants (SNRs) are the imprints of stars that died ing front in a type Ia SN incinerates most of the progenitor to in supernova (SN) explosions on the interstellar medium (ISM). Fe-group elements. Despite the essential role of type Ia SNe SNRs return nucleosynthesis products to the ISM, enriching and in cosmology as standard candles, leading to the discovery that mixing it with freshly produced heavy elements. A core-collapse the expansion of the Universe is accelerating (Riess et al. 1998; (CC) SN is the explosion of a massive star, and it produces Perlmutter et al. 1999), the exact nature of the progenitor sys- large quantities of α-group elements (e.g. O, Ne, Mg, Si, S). tem as either a white dwarf accreting from a companion or a Thermonuclear (or type Ia) SNe mark the disruption of a carbon- merger of two white dwarves is still hotly debated (see Maoz & oxygen white dwarf (WD) that reached the Chandrasekhar limit, Mannucci 2012,forareview). although recent models suggest that sub-Chandrasekhar WDs SNe of either type instantaneously release a tremendous 51 Based on observations obtained with XMM-Newton,anESAsci- amount of kinetic energy (∼10 erg) in the ISM and conse- ence mission with instruments and contributions directly funded by quently have a profound and long-lasting impact on their sur- ESA Member States and NASA. rounding environment. SN ejecta are launched to velocities in Article published by EDP Sciences A162, page 1 of 52 A&A 585, A162 (2016) excess of 104 km s−1, producing shock waves that heat the ISM were presented in a wide collection of individual papers with lit- and ejecta up to X-ray emitting temperatures (>106 K). SNe are tle consistency in the instruments, spectral models, and analysis the main source of energy for the ISM, in the form of kinetic methods used. Furthermore, several known SNRs were observed energy and turbulence (e.g. Mac Low & Klessen 2004, and ref- for the first time with modern X-ray instrumentation during erences therein) or in the form of cosmic rays that are accelerated our XMM-Newton LMC survey (see Sect. 2.1) and their spectral at SNR shock fronts. properties are as yet unpublished (see Sect. 5.1 and Appendix D). X-ray observations are a powerful tool for studying SNRs Because of these limitations, it is not feasible to study the spec- (see e.g. the review of Vink 2012). While some SNRs ex- tral properties of the whole population of LMC remnants with a hibit non-thermal X-ray emission, originating in synchrotron- mere survey of the available literature. emitting electrons accelerated up to 100 TeV (see Koyama The main ambition of this work is to alleviate these limita- et al. 1995; Rho et al. 2002; Bamba et al. 2005, and refer- tions and provide for the first time an up-to-date study of the ences therein), most X-ray emitting SNRs have thermal spectra X-ray emission of LMC SNRs, using primarily XMM-Newton dominated by highly ionised species of C, N, O, Ne, Mg, Si, observations. To that end, we performed a systematic and ho- S, and Fe. At the typical electron temperatures of SNR shocks mogeneous X-ray spectral analysis of all LMC SNRs for which (kT ∼ 0.2−5 keV), all these astrophysically abundant elements XMM-Newton data are available. This allows meaningful com- have emission lines in the range accessible to X-ray space obser- parisons of remnants at various evolutionary stages, and provides vatories. Thus, the thermal X-ray spectrum of an SNR encrypts a complete census of various spectral features, such as Fe K or precious information about the temperature, ionisation state, and SN ejecta emission. In turn, SNRs are used as probes of their chemical composition of the hot plasma (Slane 2014). This, in surroundings, thanks to which one can derive the chemical abun- turn, provides clues to the evolutionary state of the remnant, am- dances in the hot phase of the LMC ISM, and compare those to bient density (of the inter- or circum-stellar medium), age, explo- abundances measured in older populations (globular clusters and sion energy, and the type of supernova progenitor. The distribu- red giant stars). tion of these parameters, the impact of the environment on them, In addition, we take advantage of the availability of star for- and their interrelations (e.g. temperature vs. size/age, luminos- mation history (SFH) maps of the LMC, based on spatially re- ity vs. ambient density) are valuable information to understand solved stellar photometry, to investigate the connection between the evolution of SNRs and their role in the hydrodynamical and LMC SNRs and their local environment, characterised by differ- chemical evolution of galaxies. ent SFHs. Doing so, we devise a method to tentatively type all Furthermore, SNRs are observable for a few tens of thou- LMC SNRs, which can then be used to retrieve the ratio of core- sands of years. Thus, even though SNe are rare events in a galaxy collapse to type Ia SN rates in the LMC. Then, via their X-ray (typically one per century or less), there will be tens or hundreds luminosity function, we compare SNR populations in galaxies of of SNRs for us to access. In our own Galaxy, the Milky Way the Local Group (M31, M33, LMC, SMC), which have different (MW), 294 SNRs are known (Green 2014). However, studies of metallicities and SFHs. Finally, we study the spatial distribution Galactic SNRs are plagued by the large distance uncertainties to- of SNRs in the LMC with respect to cool gas, star-forming re- wards sources in the Galactic plane.
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