TY - JOUR
T1 - Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
AU - Iaria, Rosario
AU - Di Salvo, Tiziana
AU - D'Aì, null
AU - Riggio, null
AU - Bozzo, null
AU - Pintore, null
AU - Sanna, null
AU - Burderi, null
AU - Papitto, null
AU - Ferrigno, null
PY - 2017
Y1 - 2017
N2 - 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.
AB - 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.
KW - Astronomy and Astrophysics
KW - Pulsars: individual: IGR J00291+5934
KW - Space and Planetary Science
KW - Stars: neutron
KW - X-rays: binaries
KW - Astronomy and Astrophysics
KW - Pulsars: individual: IGR J00291+5934
KW - Space and Planetary Science
KW - Stars: neutron
KW - X-rays: binaries
UR - http://hdl.handle.net/10447/228373
UR - http://mnras.oxfordjournals.org/
M3 - Article
VL - 466
SP - 3450
EP - 3459
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
ER -