RXTE observations of RX J0146.9+6121: a new X-ray outburst of the Be/X-ray pulsar

RXTE observations of the Be/X-ray binary pulsar RX J0146.9+6121 in July 1997 revealed the begin of a new Xray outburst, the second observed after its discovery in August 1984 by EXOSAT. The flux increased by nearly a factor of five within one week reaching 3.2 10−10 erg cm−2 s−1. The corresponding X-ray luminosity for a distance of 2.5 kpc is an order of magnitude brighter than the level observed between 1994 and 1996 by ASCA and ROSAT. The neutron star spin period was measured to 1404.2 ± 1.2 s indicating the start of a spin-up phase as expected for increased matter accretion onto the neutron star during outburst. A combined spectral analysis of ASCA and RXTE data revealed an exponential cutoff in the power-law spectrum at 4 keV.