(a) HC₃N J = 2−1, F = 3− 2 spectrum of the peak position. Red lines show the Gaussian fitting. (b) Zoom-in of panel a showing line wing of HC₃ N J = 2− 1, F = 3− 2. (c) Background is integrated map of HC₃N J = 2−1, F = 3− 2. Black contours represent integration of red wing (6.75–7.08 km s⁻¹) of HC₃ N J = 2–1, F = 3–2 stepped from 60 to 90% by 10% of maximum value 0.14 K km s⁻¹. The red contour denotes 3σ level (0.06 K km s⁻¹) of HC₃ N wing integration.The filled black square represents O point, and the black triangle represents P point (see text). The IRS is shown by the hexagonal star (Yen et al. 2014). Small black crosses show sampled points of K_u band observation.