  We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a
structure with a strong cool core in a near redshift ($z = 0.216$). We
performed a combined analysis using photometric and spectroscopic data obtained
at Gemini South Telescope. We estimated the cluster mass through gravitational
lensing, obtaining $M_{200} = 5.3\pm0.4 \times 10^{14}$ $h_{70}^{-1}$ M$_\odot$
within $R_{200} = 1.56 \pm 0.04$ $h^{-1}_{70}$ Mpc, in agreement with a virial
mass estimate. This cluster presents a prominent filamentary structure
associated to its BCG, located mainly along its major axis and aligned with the
X-ray emission. A combined study of three emission line diagnostic diagrams has
shown that the filament emission falls in the so-called transition region of
these diagrams. Consequently, several ionizing sources should be playing an
meaningful role. We have argued that old stars, often invoked to explain LINER
emission, should not be the major source of ionization. We have noticed that
most of the filamentary emission has line ratios consistent with the shock
excitation limits obtained from shock models. We also found that line fluxes
are related to gas velocities (here estimated from line widths) by power-laws
with slopes in the range expected from shock models. These models also show,
however, that only ~10% of H$\alpha$ luminosity can be explained by shocks. We
conclude that shocks probably associated to the cooling of the intracluster gas
in a filamentary structure may indeed be contributing to the filament nebular
emission, but can not be the major source of ionizing photons.
