Journal Article

Flares, broadening of the pulse-frequency peak and quasi-periodic oscillations in the transient X-ray pulsar 4U 1901+03

Marykutty James, Biswajit Paul, Jincy Devasia and Kavila Indulekha

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 3, pages 1489-1495
Published in print January 2011 | ISSN: 0035-8711
Published online January 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17543.x
Flares, broadening of the pulse-frequency peak and quasi-periodic oscillations in the transient X-ray pulsar 4U 1901+03

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After a long quiescence of three decades, the transient X-ray pulsar 4U 1901+03 became highly active in 2003 February. From the analysis of a large number of Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) observations of this source, we report here the detection of X-ray flares, a broadening of the pulse-frequency feature and quasi-periodic oscillations (QPOs). The X-ray flares showed spectral changes, had a duration of 100–300 s, and were more frequent and stronger during the peak of the outburst. In most of the observations during the outburst we also detected a broadening of the pulse-frequency peak. We have also found intensity-dependent changes in the pulse profile at very short time-scales. This reveals a coupling between the periodic and the low-frequency aperiodic variabilities. In addition, near the end of the outburst we have detected a strong QPO feature centred at ∼0.135 Hz. The QPO feature is broad with a quality factor of 3.3 and with an rms value of 18.5 ± 3.1 per cent. Using the QPO frequency and the X-ray luminosity during the QPO detection period we estimated the magnetic field strength of the neutron star as 0.31 × 1012 G which is consistent with the value inferred earlier under the assumption of spin equilibrium.

Keywords: stars: individual: 4U 1901+03; stars: neutron; pulsars: individual: 4U 1901+03; X-rays: binaries; X-rays: stars

Journal Article.  4194 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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