Ly$\alpha$ view around a z=2.84 hyperluminous QSO at a node of the
  cosmic web
  We report on the results of deep and wide-field (1.1 deg$^2$) narrow-band
observations with Subaru/Hyper Suprime-Cam (HSC) of a field around a
hyperluminous QSO (HLQSO), HS1549+1919, residing in a protocluster at $z=2.84$,
to map the large-scale structure of Ly$\alpha$ emitters (LAEs). One HSC
pointing enables us to detect 3490 LAEs and 76 extended Ly$\alpha$ blobs
(LABs), probing diverse environments from voids to protoclusters. The HLQSO is
found to be near the center of the protocluster, which corresponds to the
intersection of $\sim$100 cMpc-scale structures of LAEs. LABs are basically
distributed along the large-scale structure, with larger ones particularly
clustered around the HLQSO, confirming a previously noted tendency of LABs to
prefer denser environments. Moreover, the shapes of LABs near the HLQSO appear
to be aligned with the large-scale structure. Finally, a deep Ly$\alpha$ image
reveals a diffuse Ly$\alpha$ nebula along a filamentary structure with no
luminous UV/sub-mm counterpart. We suggest that the diffuse nebula is due to a
cold filament with high clumping factor illuminated by the QSO, with a required
high clumpiness provided by unresolved residing halos of mass $\leq
10^{9-10}M_\odot$.
