We report the discovery of a giant radio halo in the galaxy cluster RXC J1514.9-1523 at z=0.22 with a relatively low X-ray luminosity , L _ { X [ 0.1 - 2.4 kev ] } \sim 7 \times 10 ^ { 44 } erg s ^ { -1 } .
This faint , diffuse radio source is detected with the Giant Metrewave Radio Telescope at 327 MHz .
The source is barely detected at 1.4 GHz in a NVSS pointing that we have reanalyzed .
The integrated radio spectrum of the halo is quite steep , with a slope \alpha = 1.6 between 327 MHz and 1.4 GHz .
While giant radio halos are common in more X-ray luminous cluster mergers , there is a less than 10 % probability to detect a halo in systems with L _ { X } \raise 2.0 pt \hbox { $ < $ } \kern - 6.0 pt \lower 4.0 pt \hbox { $ \sim$ } 8 \times 10 ^ { 44 } erg s ^ { -1 } .
The detection of a new giant halo in this borderline luminosity regime can be particularly useful for discriminating between the competing theories for the origin of ultrarelativistic electrons in clusters .
Furthermore , if our steep radio spectral index is confirmed by future deeper radio observations , this cluster would provide another example of the recently discovered population of ultra-steep spectrum radio halos , predicted by the model in which the cluster cosmic ray electrons are produced by turbulent reacceleration .