RXTE OBSERVATIONS OF RX J0146.9- A NEW X-RAY OUTBURST OF THE BE(6121 )X-RAY PULSAR/

RXTE observations of the Be/X-ray binary pulsar RXJ0146.9+6121 in July 1997 revealed the begin of a new Xray outburst, the second observed a fter its discovery in August 1984 by EXOSAT. The flux increased by nea rly 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 an d 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 exponen tial cutoff in the power-law spectrum at 4 keV.