Multiwavelength Analysis of A1240, the Double Radio Relic Merging Galaxy
  Cluster Embedded in a ~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 a ~4 Mpc filamentary structure elongated in the north-south
orientation. The northern ($M_{200}=2.61_{-0.60}^{+0.51}\times10^{14}
M_{\odot}$) and middle ($M_{200}=1.09_{-0.43}^{+0.34}\times10^{14} M_{\odot}$)
mass clumps separated by ~1.3 Mpc are associated with A1240 and co-located with
the X-ray peaks and cluster galaxy overdensities revealed by Chandra and
MMT/Hectospec observations, respectively. The southern mass clump
($M_{200}=1.78_{-0.55}^{+0.44}\times10^{14} M_{\odot}$), ~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 post-merger binary system in the returning phase
with the time-since-collision ~1.7 Gyr. With the SDSS DR16 data analysis, we
also find that A1240 is embedded in the much larger-scale (~80 Mpc) filamentary
structure whose orientation is in remarkable agreement with the hypothesized
merger axis of A1240.
