The ASKAP-EMU survey is a deep wide-field radio continuum survey designed to cover the entire southern sky and a significant fraction of the northern sky up to +30 ^ { \circ } .
Here , we report a discovery of a radio relic in the merging cluster SPT-CL 2023-5535 at z = 0.23 from the ASKAP-EMU pilot 300 sq .
deg survey ( 800 - 1088 MHz ) .
The deep high-resolution data reveal a \raise 0.817 pt \hbox { $ \scriptstyle \sim$ } 2 Mpc-scale radio halo elongated in the east-west direction , coincident with the intracluster gas .
The radio relic is located at the western edge of this radio halo stretched \raise 0.817 pt \hbox { $ \scriptstyle \sim$ } 0.5 Mpc in the north-south orientation .
The integrated spectral index of the radio relic within the narrow bandwidth is \alpha ^ { \scriptstyle 1088 ~ { } MHz } _ { \scriptstyle 800 ~ { } MHz } = -0.76 \pm 0.06 .
Our weak-lensing analysis shows that the system is massive ( M _ { 200 } = 1.04 \pm 0.36 \times 10 ^ { 15 } ~ { } M _ { \sun } ) and composed of at least three subclusters .
We suggest a scenario , wherein the radio features arise from the collision between the eastern and middle subclusters .
Our discovery illustrates the effectiveness of the ASKAP-EMU survey in detecting diffuse emissions in galaxy clusters and when completed , the survey will greatly increase the number of merging cluster detections with diffuse radio emissions .