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Astron. Astrophys. 346, 929-935 (1999)

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

G.L. Israel *  1, T. Oosterbroek 2, L. Angelini **  3, S. Campana[FORMULA]  4, S. Mereghetti 5, A.N. Parmar 2, A. Segreto 6, L. Stella[FORMULA]  1, J. van Paradijs 7,8 and N.E. White 3

1 Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio Catone (Roma), Italy
2 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
3 Laboratory for High Energy Astrophysics, Code 662, NASA - Goddard Space Flight Center, Greenbelt, MD 20771, USA
4 Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (Lecco), Italy
5 Istituto di Fisica Cosmica "G. Occhialini", CNR, Via Bassini 15, I-20133 Milano, Italy
6 Istituto di Fisica Cosmica ed Applicazioni all'Informatica, CNR, Via U. La Malfa 153, I-90146 Palermo, Italy
7 Astronomical Institute "Anton Pannekoek" and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
8 Physics Department, UAH, Huntsville, AL 35899, USA

Received 26 January 1999 / Accepted 30 March 1999

Abstract

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 P_ [FORMULA] 2[FORMULA]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 ([FORMULA] [FORMULA] 4) plus a blackbody with kT [FORMULA] 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.

Key words: stars: evolution – stars: neutron – stars: pulsars: individual: 4U 0142+61 – X-rays: stars

* Affiliated to I.C.R.A.
** Universities Space Research Association

Send offprint requests to: G.L. Israel (israel@coma.mporzio.astro.it)

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© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999
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