Multiwavelength Analysis of A1240, the Double Radio-relic Merging Galaxy Cluster Embedded in an similar to 80 Mpc-long Cosmic Filament

We present a multiwavelength study of the double radio-relic cluster A1240 at z = 0.195. Our Subaru-based weak-lensing analysis detects three mass clumps forming an similar to 4 Mpc filamentary structure elongated in a north-south orientation. The northern (M-200 = 2.61(-0.60)(+0.51 )x 10(14)M(circle dot)) and middle (M-200 = 1.09(-0.43)(+0.34) x 10(14)M(circle dot)) mass clumps separated by similar to 1.3 Mpc are associated with A1240 and colocated with the X-ray peaks and cluster galaxy overdensities revealed by Chandra and MMT/Hectospec observations, respectively. The southern mass clump (M-200 = 1.78(-0.55)(+0.44) x 10(14)M(circle dot)), similar to 1.5 Mpc to the south of the middle clump, coincides with the galaxy overdensity in A1237, the A1240 companion cluster at z = 0.194. Considering the positions, orientations, and polarization fractions of the double radio relics measured by the LOFAR study, we suggest that A1240 is a postmerger binary system in the returning phase with a time since collision of similar to 1.7 Gyr. With the SDSS DR16 data analysis, we also find that A1240 is embedded in the much larger scale (similar to 80 Mpc) filamentary structure whose orientation is in remarkable agreement with the hypothesized merger axis of A1240.