Multi-frequency radio-continuum study of the LMC SNR N206 (Goat's Eye) and its "zig-zag" PWN

Abstract

We present new radio-continuum observations of the Large Magellanic Cloud (LMC) supernova remnant (SNR) N206, which we give the name "Goat's Eye". Goat's Eye contains an interior radio structure that is likely a pulsar wind nebula (PWN), which we analyse in further detail. We use new radio observations from the Australia Telescope Compact Array (ATCA) telescope, as well as several archival radio observations, to calculate spectral indices, and find a steep spectral index for the whole SNR ($α= -0.60\pm0.02$), and a flatter spectral index for the PWN ($α= -0.16\pm0.03$). We also measure the polarisation and magnetic field properties of the PWN. Previously reported as a linear structure, the new observations show an unusual "zig-zag"-like structure, visible in radio-continuum total intensity, linear polarisation, and magnetic field orientations. The origin of this zig-zag structure is unclear, but we propose some origin scenarios that will require further observations to differentiate between.

Figures (8)

• Figure 1: Multi-frequency composite colour image of Goat's Eye. Red is radio-continuum MeerKAT data (1.3 GHz), green is optical DeMCELS [S ii] data, blue is soft X-ray XMM-Newton data (0.2$-$1.0 keV), yellow is optical MCELS [O iii] data, and cyan is hard X-ray XMM-Newton data (2.0$-$4.5 keV). All images are linearly scaled.
• Figure 2: 4-panel image of Goat's Eye. All images have linear scaling and display a relevant scale bar in the bottom right corner. Top left: MeerKAT radio-continuum image at 1.3 GHz. The left inset shows a zoomed-in ATCA 5.5 GHz view of the PWN. The described "zig-zag" structure is annotated with the black line and the position of the X-ray point source possible pulsar is shown in the blue circle. The beam size of 5$^{\prime\prime}$$\times$5$^{\prime\prime}$ is shown in the bottom left corner. The top right image shows the same PWN view using an X-ray RGB made with Chandra data. Red is soft band (0.5$-$1.2 keV), green is medium band (1.2$-$2.0 keV), and blue is hard band (2.0$-$7.0 keV). Contours are from the left-hand ATCA image at levels of 0.4 and 0.8 mJy beam$^{-1}$. Top right: Multi-frequency RGB where red is MeerKAT radio at 1.3 GHz, green is DeMCELS H$\alpha$, and blue is XMM--Newton soft X-ray (0.2--1.0 keV). Bottom left: Optical RGB where red is DeMCELS H$\alpha$, green is DeMCELS [S ii] and blue is MCELS [O iii]. Bottom right:XMM--Newton X-ray RGB where red is soft X-ray (0.2--1.0 keV), green is medium X-ray (1.0--2.0 kev), and blue is hard X-ray (2.0--4.5 keV).
• Figure 3: Radio-continuum spectrum of Goat's Eye using radio-continuum data from (Table \ref{['tabflux']}). The black solid line gives the total spectral index, the black dashed line gives the PWN spectral index, and the black dotted line gives the shell spectral index, as shown in the legend. The points in red are the non-fitted data in Table \ref{['tabflux']}.
• Figure 4: [S ii]/H${\alpha}$ ratio map of Goat's Eye from optical DeMCELS data. The contours are from the MeerKAT radio-continuum image at levels of 0.3, 0.8, and 2.0 mJy beam$^{-1}$.
• Figure 5: H i integrated intensity map and $p-v$ diagram of Goat's Eye and surrounding environment. Panel (a): H i intensity map of Goat's Eye and surrounding environment integrated over the $V_\mathrm{LSR}$ velocity range of 214.2--226.6 km s$^{-1}$. Black contours are from MeerKAT 1.3 GHz radio-continuum map at levels of 0.5, 1.0, 1.5, and 2.0 mJy beam$^{-1}$. The dashed white horizontal lines correspond with panel (b) and show the extent of the possible H i cavity. Panel (b): H i$p$--$v$ diagram, integrated over Goat's Eye's Dec location ($-$71$.\!\!^\circ$02-- --70$.\!\!^\circ$99). The dashed white horizontal lines correspond with panel (a) showing the location of the cavity relative to Goat's Eye. The black dashed arc traces the possible H i cavity, and the labelled arrows display the PWN and SNR physical extents.