BeppoSAX monitoring of the "anomalous" X-ray pulsar 4U 0142+61

The 8.7 s X-ray pulsar 4U0142+61 was monitored by BeppoSAX between January 1997 and February 1998. This source belongs to the rapidly growing class of "anomalous" X-ray pulsars (AXPs) which have pulse periods in the 6-12 s ra nge and no plausible optical, infrared or radio counterparts. The BeppoSAX periods measurements show that 4U0142+61 continues its spin-down at a nearl y constant rate of P similar to 2 x 10(-12) s s(-1). The 0.5-10 keV pulse s hape is double peaked. The phase-averaged spectrum can be described by a st eep absorbed power-law (Gamma similar to 4) plus a blackbody with kT simila r to 0.4 keV. 4U0142+61 was also detected serendipitously in a March 1996 RXTE observatio n pointed towards the nearby 1455 s Xray pulsar RX J0146.9+6121. The timing analysis results are reported for this observation and the spin history of 4U 0142+61 since 1979 is discussed.