XTE J1739−285

XTE J1739−285 is a neutron star,^[2] in the constellation Ophiuchus, situated approximately 39,000 light-years from Earth. It was first observed on 19 October 1999 by NASA's Rossi X-ray Timing Explorer satellite.

XTE J1739−285

Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus
Right ascension	17h 39m 53.95s
Declination	−28° 29′ 46.8″
Characteristics
Spectral type	Q
Variable type	None
Astrometry
Distance	39,000 Ly
Details
Mass	1.51[1] M☉
Radius	10.9 km
Other designations
SWIFT J1740.6−2821B
Database references
SIMBAD	data

It had previously been claimed that XTE J1739−285 was the fastest-spinning celestial body yet known, with a frequency of 1122 Hz.^[3] However, a re-analysis of these data by other astronomers has been unable to reproduce this result.^[4]

XTE J1739−285 has been proposed as a possible quark star, as well as 3C 58.