Three-Dimensional Kinematics of the Oxygen-rich Supernova Remnant G292.0+1.8

TL;DR

The study addresses how the oxygen-rich ejecta of the young SNR G292.0+1.8 occupy a 3D structure and what this reveals about the underlying core-collapse explosion. By combining prior proper-motion data with new radial-velocity measurements from [O III] spectra of 93 knots under a free-expansion assumption, the authors construct a 3D kinematic model that shows a broad bi-conical, bipolar expansion along a roughly North–South axis. They also detect oxygen-burning products, including sulfur, across knots with a wide range of velocities, indicating substantial mixing and an asymmetric explosion. These findings enhance our understanding of explosion geometry in CC SNe and motivate comprehensive IFU surveys to map entire remnants for robust comparisons with X-ray and radio data, thereby constraining progenitor properties and explosion mechanisms.

Abstract

Studying the remnants of young core-collapse supernovae (SNe) can yield insight into the chemical composition of their progenitors and the geometry of the explosions. The supernova remnant (SNR) G292.0+1.8 is one of only three known oxygen-rich SNRs in the galaxy-remnants of core-collapse for which relatively pure fragments of ejecta can be seen. Several dozen ejecta knots from G292.0+1.8 were the subject of a proper motion analysis, based on [O III] 5007-Angstrom images taken over a 22-year baseline by Winkler et al. 2009 (arXiv:0810.1935). They determined that the transverse velocities of the filaments are linearly proportional to their distances from a common expansion center, thus the O-rich filaments have been traveling with little deceleration since the initial supernova event,about 3000 years ago. In this paper, we use optical spectra of G292.0+1.8, all taken from the Cerro Tololo Inter-American Observatory (CTIO), to measure radial velocities for 93 knots. Assuming un-decelerated expansion, as indi- cated by the proper motions, the radial velocity should be proportional to the distance from the center along the line of sight, just as the proper motions are proportional to the transverse distance. Therefore, we can map the three-dimensional structure and kinematics of the SNR. We find that the knots generally follow a broad bi-conical distribution, suggesting that the supernova explosion produced broad jets of ejecta. This structure is similar to that seen in some other young core-collapse supernova remnants.

Figures (6)

• Figure 1: Continuum-subtracted [O3] image of G292.0+1.8, with the five R-C spectrograph slit positions indicated in red. The 68 spatially distinct knots used in this analysis indicated by blue circles. These include both knots lying along the R-C spectrograph slits and those targeted with Hydra.
• Figure 2: (a, top) One-dimensional spectra for four knots located along the northernmost slit. These spectra were extracted from the same 2-D spectrum, which was the combination of five exposures taken on the first night of observations with the R-C spectrograph on the 1.5m telescope. These are typical of the G292 knots. [O3] $\:\lambda\lambda$ 4959, 5007 is prominent in all the knots, while a fraction of them also have strong [S2] $\:\lambda\lambda$ 6716, 6731. Note the complete absence of Balmer lines. (b, bottom) Enlargement of first and third (from bottom) spectra above, emphasizing the Doppler shifts.The lower spectrum is redshifted, while the upper one is blueshifted.
• Figure 3: Continuum-subtracted [O3] image of G292 showing locations of knots for which optical spectra were extracted. Color coding indicates Doppler shift: red circles indicate knots with $v_{rad} > 330 \:\rm{\,km\,s^{-1}}$, blue circles indicate $v_{rad} < -330 \:\rm{\,km\,s^{-1}}$, and green squares indicate $-330 \:\rm{\,km\,s^{-1}} <$$v_{rad}$$< 330 \:\rm{\,km\,s^{-1}}$. For clarity, smaller symbols are used for some knots with multiple kinematic components. Knots in the northern region are mostly blue-shifted, while knots in the bright eastern spur and the south are mostly red-shifted. The yellow cross marks the expansion center from WTRL.
• Figure 4: The 3-D morphology of optical knots in G292 presented as orthographic projections along the x-, y-, and z-axes. This assumes a uniform expansion model, with a distance of 6 kpc and an age of 3000 years, as described in the text. Blue circles represent knots with $v_{rad} < -330 \:\rm{\,km\,s^{-1}}$; green squares, knots with $-330 \:\rm{\,km\,s^{-1}} <$$v_{rad}$$< +330 \:\rm{\,km\,s^{-1}}$; red diamonds, knots with $v_{rad} > 330 \:\rm{\,km\,s^{-1}}$.
• Figure 5: Radial velocity $v_{rad}$ versus transverse velocity, for both [O3]-only and [O3]/[S2] knots. Transverse velocities are determined as $\sqrt{v_{x}^2+v_{y}^2}$, where velocities have been scaled to a distance of 6.0 kpc and an age of 3000 yr. For expansion in which all the knots have close to the same speed, we expect a spherical shell-like structure, which would appear as an approximately semi-circular distribution, such that the knots with highest radial velocity have the lowest transverse velocity, and vice versa. Clearly both types of knots in G292 have a wide variety of expansion speeds.