Discovery of a Supercluster in the eROSITA Final Equatorial Depth
  Survey: X-ray Properties, Radio Halo, and Double Relics
  We examine the X-ray, optical, and radio properties for the members clusters
of a new supercluster discovered during the SRG/eROSITA Performance
Verification phase. In the 140 deg2 eROSITA Final Equatorial Depth Survey
(eFEDS) field we detect a previously unknown supercluster consisting of a chain
of eight galaxy clusters at z=0.36. The redshifts of these members are
determined through HSC photometric measurements. We examine the X-ray
morphological and dynamical properties, gas and total mass out to R500 of the
members and compare them with the general population of clusters detected in
the eFEDS field. We further investigate the gas in the bridge region between
the cluster members for a potential WHIM detection. Radio follow-up
observations with LOFAR and uGMRT are used to search for diffuse emission and
constrain the dynamic state of the system. We do not find significant
differences in the morphological parameters and properties of the intra-cluster
medium of the clusters embedded in this large-scale filament compared to eFEDS
clusters. We also provide upper limits on the electron number density and mass
of the warm-hot intergalactic medium as provided by the eROSITA data. These
limits are consistent with previously reported values for the detections in the
vicinity of clusters of galaxies. In LOFAR and uGMRT follow-up observations of
the northern part of this supercluster we find two new radio relics that are
the result of major merger activity in the system. These early results show the
potential of eROSITA to probe large-scale structures such as superclusters and
the properties of their members. Our forecasts show that we will be able to
detect 450 superclusters with 3000 member clusters located in the eROSITA_DE
region at the final eROSITA all-sky survey depth, enabling statistical studies
of the properties of superclusters and their constituents embedded in the
cosmic web.
