INTEGRAL observation of the accreting pulsar 1E1145.1-6141

¹ IASF-Pa, via Ugo la Malfa 153, 90146 Palermo, Italy e-mail: ferrigno@ifc.inaf.it
² IAAT, Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany

Received: 10 September 2007
Accepted: 5 December 2007

Abstract

Aims. We analyze 1050 ks of INTEGRAL data of the high mass X-ray binary pulsar 1E 1145.1-6141 to study its properties over a long time baseline, from June 2003 to June 2004, with wide spectral coverage.

Methods. We study three high luminosity episodes, two of them at the system apoastron, three brightening with lower intensity, two at the periastron, and one extended period of intermediate luminosity spanning one orbital cycle. We perform a timing analysis to determine the pulse period and pulse profiles at different energy ranges. We also analyze the broad band phase averaged spectrum of different luminosity states and perform phase resolved spectroscopy for the first flare.

Results. From the timing analysis, we find a pulse period of ~297 s around MJD 53 000 with a significant scatter around the mean value. From the spectral analysis we find that the source emission can be described by an absorbed bremsstrahlung model in which the electron temperature varies between ~25 and ~37 keV, without any correlation with luminosity, and the intrinsic absorbing column is constantly of the order of . Phase resolved spectral analysis reveals a different temperature of the plasma in the ascending and descending edges of the pulse during the first flare. This justifies the pulse maximum shift by ~0.4 phase units between 20 and 100 keV observed in the pulse profiles.

Conclusions. The comparison with the previous period measurements reveals that the source is currently spinning down, in contrast to the long term secular trend observed so far, indicating that at least a temporary accretion disk is formed. The study of the spectral property variations with respect to time and spin phase suggests the presence of two emitting components at different temperatures whose relative intensity varies with time.