  We use time resolved spectroscopy of thermonuclear X-ray bursts observed from
SAX J1748.9-2021 to infer the mass and the radius of the neutron star in the
binary. Four X-ray bursts observed from the source with RXTE enable us to
measure the angular size and the Eddington limit on the neutron star surface.
Combined with a distance measurement to the globular cluster NGC 6440, in which
SAX J1748.9-2021 resides, we obtain two solutions for the neutron star radius
and mass, R = 8.18 +/- 1.62 km and M = 1.78 +/- 0.3 M_\sun or R = 10.93 +/-
2.09 km and M = 1.33 +/- 0.33 M_\sun.

High Energy Astrophysical Phenomena