A Second Intense Burst with Photospheric Radius Expansion from X2127+119 in M15

In 2000 September we observed a bright X-ray burst from X2127+119 with the Rossi X-ray Timing Explorer. This burst has a multi-peaked profile, a peak luminosity of ~6.5x10^{38} erg s^{-1}, a total integrated energy of ~2x10^{40} ergs, and significant photospheric radius expansion to a maximum extent of R=118+-5 km. From the luminosity-temperature relation during the expansion phase we derive estimates for the gravitational redshift at the neutron star surface, the corrected Eddington luminosity, and the neutron star mass. We detect no slow (~30s) radial oscillations or fast (100-1200 Hz) coherent oscillations or QPO during the burst. The 2000 September event is only the second burst ever observed from this globular cluster binary (in M15 = NGC 7078), and it shares many characteristics with the event detected by Ginga in 1988 October (Dotani et al. 1990; van Paradijs et al. 1990), the key difference probably being the total amount of material consumed in the thermonuclear flash.