Discovery of pulsations in the X-ray transient 4U 1901+03
Back in 2003 we made RXTE observations of a new outburst of an old transient last seen in the early '70s, 4U 1901+03. We found pulsations at 2.763 s and an almost-circular orbit with period 22.58 d. Like KS 1947+30, this likely Be-X-ray binary has a much smaller than expected eccentricity of 0.036, suggesting that the natal kick from the supernova explosion which formed the neutron star was unusually small.
Read the paper (accepted by ApJ)
See also ATel #121
RXTE observations reveal the 18.7 s
pulsar KS 1947+30 to be in an almost circular 40.415 d orbit. We found evidence for a
"glitch" - an abrupt increase in the neutron star spin frequency - previously observed
only in radio pulsars and AXPs.
