Discovery of a new X-ray burst/millisecond accreting pulsar HETE J1900.1-2455

A class of low-mass X-ray binary sources are known to be both X-ray burst sources and millisecond pulsars at the same time. A new source of this class was discovered by High Energy Transient Explorer 2 (HETE-2) on 14 June 2005 as a source of type-I X-ray bursts, which was named HETE J1900.1-2455. Three (two triggered and one untriggered) X-ray bursts from HETE J1900.1-2455 were observed during the summer of 2005. We report the properties of these three bursts of HETE J1900.1-2455. The time resolved spectral analysis for these bursts have revealed that the spectra are consistent with the blackbody radiation throughout the bursts. The bursts show the indication of radius expansion. The bolometric flux remains almost constant during the first 13 sec of a burst while the photospheric radius and black-body temperature changed during the same period. Assuming the flux reached to the Eddington limit and standard 1.4 solar mass neutron star with helium atmosphere, we can estimate the distance to the source as 5 kpc.