The red circles in the RASS photon images (left, in the 0.5 − 2 keV energy band) indicate the position and extent of the detection from X22. The dashed magenta circles show the FoV of the XMM-Newton observation, and the green boxes serve as a 1° ×1° ruler. The blue contours show the smoothed signal from the wavelet filtered images used to detect the source. The XMM-Newton count-rate images (right, 0.4 − 1.25 keV) are instrumental-background-subtracted and smoothed by a 7.5′′ Gaussian kernel. The labels indicate the position of the main sources discussed in the paper. The white circles mark the R₅₀₀ (0.5 R₅₀₀ when dashed) of the groups that we determined in this study (Sect. 4). Magenta circles around known galaxy clusters have an arbitrary size of 2′. Matching known galaxies from NED are marked with small circles of various colors and were used for group and cluster redshift estimates (Sect. 3): Panel b: for Group 1 in green and Group 2 in cyan. Panel d: for Group 3 none, AS0924 and A3742 in green, and A3745 in yellow. Panel f: for Group 4 and [TKK2018] 859 in green and A0349 in yellow. (a) RASS image of RXGCC 127. (b) XMM-Newton image of RXGCC 127. (c) RASS image of RXGCC 841. (d) XMM-Newton image of RXGCC 841. (e) RASS image of RXGCC 104. (f) XMM-Newton image of RXGCC 104.