The 8.7 s X–ray pulsar 4U 0142+61 was monitored by Beppo SAX 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 range and no plausible optical , infrared or radio counterparts .
The Beppo SAX periods measurements show that 4U 0142+61 continues its spin–down at a nearly constant rate of Ṗ \sim 2 \times 10 ^ { -12 } s s ^ { -1 } .
The 0.5–10 keV pulse shape is double peaked .
The phase–averaged spectrum can be described by a steep absorbed power–law ( \Gamma \sim 4 ) plus a blackbody with kT \sim 0.4 keV .

4U 0142+61 was also detected serendipitously in a March 1996 RXTE observation pointed towards the nearby 1455 s X–ray 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 .