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INTEGRAL observation of the accreting pulsar GX 1+4 \ud

By C. Ferrigno, A. Segreto, A. Santangelo, J. (Joern) Wilms, I. Kreykenbohm, M. (Mirosław) Denis and R. Staubert


Aims. We present the results of the INTEGRAL monitoring campaign on the accreting low mass X-ray binary pulsar GX 1+4 performed during the Galactic plane scan of the INTEGRAL Core Programme.\ud Methods. The source was observed in different luminosity states ranging from L20−40 keV = 1.7 × 10−10 erg cm−2 s−1, to L20−40 keV = 10.5 × 10−10 erg cm−2 s−1 for about 779 ks from March 2003 until October 2004.\ud Results. Our observations confirm the secular spin down of GX 1+4 with the spin period (Ps) varying from 139.63 s to 141.56 s. In the highest luminosity state, a spin-up phase is observed. The phase-averaged spectrum of the source was modelled either with an absorbed cut-off power law or with a Comptonization model with significantly different parameters in the two brightest luminosity\ud states. No evidence of any absorption-like feature is observed in the phase averaged spectrum up to 110 keV. At highest luminosity, the source is found to pulsate up to 130 keV. Phase resolved spectroscopy reveals a phase-dependent continuum and marginal evidence for\ud an absorption feature at 34 ± 2 keV in the descending part of the pulse. If interpreted as due to electron resonant cyclotron scattering, the magnetic field in the emitting region would be (2.9 ± 0.2) × 1012(1 + z)G where z is the gravitational red shift of the emitting region. We also observed a very low luminosity state, typical of this source, which lasted for about two days during which the source spectrum was modelled by a simple power law, and a pulsed signal was still detectable in the 15−100 keV energy range

Topics: QB
Publisher: EDP Sciences
Year: 2007
OAI identifier: oai:wrap.warwick.ac.uk:3473

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