The precessing jet axis of the supernova remnant 3C 397

Abstract

We identify an S-shaped morphological feature in the enigmatic supernova remnant (SNR) 3C 397, which we attribute to the shaping by a precessing pair of jets during the explosion. We identify an S-shaped, faint region composed of two bubbles, located to the north and south of the center, between two X-ray-bright sides. We attribute the S-shape to a pair of precessing jets that were part of the explosion process. The identification of a main jet axis in SNR 3C 397 increases its similarity to the enigmatic SNR W49B. We discuss two possible scenarios for SNR 3C 397 and W49B. (1) The thermonuclear common-envelope-jet supernova scenario, which was suggested before for W49B, where a neutron star destroys a white dwarf and accretes part of the white dwarf's material via an accretion disk that undergoes a thermonuclear outburst and launches the jets. (2) The collapse-induced thermonuclear jet-driven explosion, which is a core-collapse supernova driven by jets, as in the majority of, or even all, core-collapse supernovae, and in addition, there is a thermonuclear outburst of a rare helium-oxygen mixed layer in the core, which is triggered by the core collapse. Our study emphasizes the primary role of jets even in the enigmatic SNR 3C 397.

Figures (5)

• Figure 1: A Chandra $0.5-8 {~\rm keV}$ X-ray image of SNR 3C 397. The data were processed using Gaussian smoothing with a radius of $r=20~{\rm pixels}$ and $\sigma=10~{\rm pixels}$. White contours mark the count levels for this smoothing with values of $({\rm count/pixel}) = 0.55$, $0.93$, $1.2$, $1.4$, $2.1$, $2.8$, $3.25$. The units of the color-bar are counts/pixel. We mark several bright clumps on each side of the remnant, and the faint zones extending north and south of the bright bar near the center, which we term the north and south bubbles. The north and south rims extend from one side towards the bubbles. The S-shaped profile we draw with the yellow curve passes through the two bubbles; it is point-symmetric around the 'X' point, i.e., the north and south parts are $180^\circ$ apart. We attribute the formation of the two S-shaped bubbles to a precessing jet pair during the explosion.
• Figure 2: (a) Same data, contours, and S-shaped yellow line as in Figure \ref{['Fig:MaxSmLarge']}, but a finer Gaussian smoothing with $r=11~{\rm pixels}$ and $\sigma=5.5~{\rm pixels}$. Values of colors according to the color bar in units of (count/pixel). (b) Same data, contours, and S-shaped yellow line as in panel (a), but an even finer Gaussian smoothing with $r=2~{\rm pixels}$ and $\sigma=1~{\rm pixel}$. Values of colors according to the color bar in units of count/pixel. The double-sided red arrow has its center at the 'X', i.e., the center of the S-shaped yellow line, and points to the north and south rims to emphasize the point-symmetric structure of the bubbles' boundaries. Note the different color bars in the two panels and from Figure \ref{['Fig:MaxSmLarge']}.
• Figure 3: X-ray maps of SNR 3C 397 in different lines as indicated in each panel. Contours and S-shaped yellow line as in Figure \ref{['Fig:MaxSmLarge']}. Values of colors according to the different color bars. In panels (a) and (b), the images were binned with $4 \times 4$ pixels$^2$ and smoothed with a Gaussian function with $r=10~{\rm pixels}$ and $\sigma=5~{\rm pixels}$. In panel (c), the image was binned with $16 \times 16$ pixels $^2$. The energy ranges in the equivalent width maps are as follows: (a) Si in the $1.78 - 1.9 {~\rm keV}$ band, (b) S in the $2.35 - 2.5 {~\rm keV}$ band, and (c) Fe in the $6.3 - 6.8 {~\rm keV}$ band.
• Figure 4: The X-ray image of 3C 397 from panel (b) of Figure \ref{['Fig:MediumSm']}. We denote point symmetry by 4 lines connecting bright clumps on the west and east sides, and going through the center (see text). In lines L2, L3, and L4, the two opposite arrows are of the same length. In lines L1 and L2, which are perpendicular to each other, the two opposite sides are $180^\circ$ to each other; in lines L2 and L3, the angle between the two sides is $165^\circ$.
• Figure 5: Comparison of W49B (left, Lopezetal2013aSokerShishkin2025W49b) and 3C 397 (right, Figures \ref{['Fig:MaxSmLarge']}-\ref{['Fig:PerpStructure']} here and SafiHarbetal2005). W49B: Center panel: Total X-ray counts Chandra ACIS image, smoothed to $\sigma=1$. Magenta line denotes the main jet axis and the dashed orange ring the circum-jet ring SokerShishkin2025W49b. The three panels at the corners of the image are smoothed line emission images of Fe (upper right), S (lower left), and Si (lower right), adapted from Lopezetal2013a. 3C 397: Similar to the left panel of W49B but for 3C 397. Panels at the edges are as in Figure \ref{['Fig:lines']}, except for Si and S being unsmoothed. Note that the color scales differ from panel to panel to highlight the distribution rather than intensity. The yellow curve is the S-shape from Figure \ref{['Fig:MaxSmLarge']}. A white horizontal line in all panels is a $1'$ scale bar. In both W49B and 3C 397, the iron emission distribution is noticeably different from that of the total and other lines. Both remnants feature a similar fainter central region in the emission, which we attribute to a main jet axis (magenta line); see SokerShishkin2025W49b for axis definition. Both remnants also exhibit a single sharp edge (green line; W49B: left; 3C 397: right).