6533b826fe1ef96bd128467a
RESEARCH PRODUCT
Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
Alessandro RiggioAntonino D'aiAlessandro PapittoR. IariaCarlo FerrignoFabio PintoreAndrea SannaLuciano BurderiT. Di SalvoEnrico Bozzosubject
Astrophysics::High Energy Astrophysical PhenomenaPulsars: individual: IGR J00291+5934FOS: Physical sciencesAstrophysics01 natural sciencesPulsarMillisecond pulsar0103 physical sciences010303 astronomy & astrophysicsSolar and Stellar Astrophysics (astro-ph.SR)PhysicsHigh Energy Astrophysical Phenomena (astro-ph.HE)Millisecond010308 nuclear & particles physicsOscillationSpectral densityAstronomyAstronomy and AstrophysicsAstronomy and AstrophysicLight curveX-rays: binarieAstrophysics - Astrophysics of GalaxiesStars: neutronBlack holeNeutron starindividual: IGR J00291+5934; Stars: neutron; X-rays: binaries; Astronomy and Astrophysics; Space and Planetary Science [Pulsars]Astrophysics - Solar and Stellar AstrophysicsSpace and Planetary ScienceAstrophysics of Galaxies (astro-ph.GA)Astrophysics - High Energy Astrophysical Phenomenadescription
In this paper, 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 was characterized by a flaring-like behavior, 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 behavior. 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 behavior. We suggest that the unusual variability of IGR J00291+5934 observed by XMM-Newton and NuSTAR could be produced by an heartbeat-like mechanism, similar to that operating 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 suggested in the literature for a number of other neutron star binaries displaying a similar behavior, cannot be solidly tested in the case of IGR J00291+5934 due to the paucity of type-I X-ray bursts observed from this source.
year | journal | country | edition | language |
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2016-11-21 |