the same spatial and spectral location, with two negative peaks at the expected position from the adopted dithering pattern, ensuring that the line is real and not spurious.

Normally, we expect an asymmetric line profile with a sharp blue edge and gradually declining red tail for Ly$\alpha$ emission at high redshift due to absorption by neutral hydrogen in the interstellar and intergalactic medium. However, most of the proposed Ly$\alpha$ detections in other $z \gtrsim 7$ candidates have not shown highly significant evidence for asymmetry, possibly due to the low S/N for most of the detections. We find that our detected line displays an asymmetric line profile, making this object one of the first notable detections of asymmetry for a $z>7$ Ly$\alpha$ line candidate. However, the significance is not strong due to the low S/N: the Gaussian line width on the blue and red side of the line is $0.33^{+5.51}_{-0.32}$ Å and $6.49^{+0.32}_{-4.76}$ Å, respectively. Due to the vicinity of a sky line located blueward of the line, the uncertainty in the line width on the blue side of the line ($\sigma_{\rm blue}$) is large, yielding a weak constraint on the ratio between the line width on the red and blue 