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Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934

Ferrigno, C. and Bozzo, E. and Sanna, A. and Pintore, F. and Papitto, A. and Riggio, A. and Burderi, L. and Di Salvo, T. and Iaria, R. and D'Aì, A. (2017) Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934. Monthly Notices of the Royal Astronomical Society, 466 (3). pp. 3450-3459. ISSN 0035-8711. doi:10.1093/mnras/stw3344.

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We report on the analysis of the peculiar X-ray variability displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80 ks-long joint NuSTAR and XMM–Newton observation performed during the source outburst in 2015. The light curve of the source is characterized by a flaring-like behaviour, with typical rise and decay time-scales of ∼120 s. The flares are accompanied by a remarkable spectral variability, with the X-ray emission being generally softer at the peak of the flares. A strong quasi-periodic oscillation (QPO) is detected at ∼8 mHz in the power spectrum of the source and clearly associated with the flaring-like behaviour. This feature has the strongest power at soft X-rays ( ≲ 3 keV). We carried out a dedicated hardness-ratio-resolved spectral analysis and a QPO phase-resolved spectral analysis, together with an in-depth study of the source-timing properties, to investigate the origin of this behaviour. We suggest that the unusual variability of IGR J00291+5934 observed by XMM–Newton and NuSTAR could be produced by a heartbeat-like mechanism, similar to that observed in black hole X-ray binaries. The possibility that this variability, and the associated QPO, are triggered by phases of quasi-stable nuclear burning, as sustained in the literature for a number of other neutron star binaries displaying a similar behaviour, cannot be solidly tested in the case of IGR J00291+5934 due to the paucity of type I X-ray bursts detected from this source.

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D'Aì, A.0000-0002-5042-1036
Additional Information:© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 December 20. Received 2016 December 19; in original form 2016 September 23. Published: 23 December 2016. We thank the anonymous referee and Phil Uttley for their precious suggestions. This work is based on observations obtained with XMM–Newton (OBSID 0744840201) and NuSTAR (OBSID 90101010002); the former is an ESA science mission with instruments and contributions directly funded by ESA Member States and USA (NASA); the latter is a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). We also exploited the ISIS functions provided by ECAP/Remeis observatory and MIT ( AP is supported via an EU Marie Skłodowska-Curie fellowship under grant no. 660657-TMSP-H2020-MSCA-IF-2014. We acknowledge the International Space Science Institute (ISSI – Bern) that funded and hosted the international team ‘The disk-magnetosphere interaction around transitional millisecond pulsars’.
Subject Keywords:stars: neutron – pulsars: individual: IGR J00291+5934 –X-rays: binaries
Issue or Number:3
Record Number:CaltechAUTHORS:20161123-122237857
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Official Citation:C. Ferrigno, E. Bozzo, A. Sanna, F. Pintore, A. Papitto, A. Riggio, L. Burderi, T. Di Salvo, R. Iaria, A. D'Aì; Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934, Monthly Notices of the Royal Astronomical Society, Volume 466, Issue 3, 21 April 2017, Pages 3450–3459,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:72281
Deposited By: Joy Painter
Deposited On:23 Nov 2016 22:49
Last Modified:11 Nov 2021 04:59

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