Journal Article

Timing and spectral studies of the transient X-ray pulsar GX 304−1 during an outburst

Jincy Devasia, Marykutty James, Biswajit Paul and Kavila Indulekha

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 1, pages 348-358
Published in print October 2011 | ISSN: 0035-8711
Published online October 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19269.x
Timing and spectral studies of the transient X-ray pulsar GX 304−1 during an outburst

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We present the timing and spectral properties of the transient X-ray pulsar GX 304−1 during its recent outburst in 2010 August, using observations carried out with the Proportional Counter Array (PCA) instrument on board the Rossi X-ray Timing Explorer (RXTE) satellite. We detected strong intensity- and energy-dependent variations in the pulse profiles during the outburst. The pulse profile showed significant evolution over the outburst. It showed complex structures consisting of a main peak with steps on both sides during the start of the outburst. On some days, a sharp dip-like feature was seen which disappeared at the end of the outburst when the profile evolved into a sinusoidal shape. At low energies, the pulse profiles appeared complex, consisting of multiple peaks and a narrow minimum. The amplitude of the second brightest peak in low energies decreased with energy, and above 12 keV the shape of the pulse profile changed to a single broad peak with a dip-like feature. The dip had energy dependence, both in phase and in width. We detected quasi-periodic oscillations (QPOs) at 0.125 Hz with a harmonic. The QPO feature had a low rms value of 2.9 per cent and it showed a positive energy dependence up to 40 keV with the rms value increasing to 9 per cent at 40 keV. The QPO frequency decreased from 0.128 to 0.108 Hz in 12 days. During most of the outburst, the 3–30 keV spectrum of GX 304−1 can be well fitted with a partial covering power-law model with a high-energy cut-off and iron fluorescent line emission. For a few of the observations carried out during the decay of the outburst, the partial covering absorption component is found to change to single-component absorption. We also found that the partial covering and high-energy cut-off parameters vary significantly with the pulse phase.

Keywords: binaries: general; pulsars: individual: GX 304−1; X-rays binaries; X-rays: individual: GX 304−1; X-rays: stars

Journal Article.  6444 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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