  We present the first results of a narrow-band photometric study of the
massive galaxy cluster XMMU J2235.3-2557 at z=1.39. We obtained deep $H$
narrow-band imaging with NIRI on Gemini North, corresponding to H-alpha
emission at the cluster's redshift. Our sample consists of 82 galaxies within a
radius of ~500 kpc, ten of which are spectroscopically confirmed cluster
members. Sixteen galaxies are identified as excess line-emitters. Among just
the excess line-emitting galaxies we find an average SFR of 3.6 +/- 1.3
Msun/yr. For spectroscopically confirmed cluster members we find a correlation
between H broad-band magnitude and SFR such that brighter galaxies have lower
SFRs. The probability that SFR and magnitude of confirmed members are
uncorrelated is 0.7%. We also find a correlation between SFR and distance from
the cluster centre for both confirmed and excess line-emitting candidate
members, with a probability of 5% for there to be no correlation among
confirmed members. All excess line-emitting candidate cluster members are
located outside a radius of 200 kpc. We conclude that star formation is
effectively shut off within the central 200 kpc radius (R_QUENCH ~ 200 kpc) of
this massive galaxy cluster at z=1.39, when the universe was only 4.5 Gyr old.
