Optical and X-Ray Observations of IGR J00291+5934 in Quiescence
Abstract
We report on optical and X-ray observations of the accretion-powered millisecond pulsar IGR J00291+5934 in quiescence. Time-resolved I-band photometry has been obtained with the 4.2 m William Herschel Telescope, while a 3 ks Chandra observation provided contemporaneous X-ray coverage. We found an unabsorbed 0.5-10 keV X-ray flux of 1 × 10-13 erg cm-2 s-1, which implies that the source was in quiescence at the time of the optical observations. Nevertheless, the optical I-band light curve of IGR J00291+5934 shows evidence for strong flaring. After removal of the strongest flares, we find evidence for an orbital modulation in the phase-folded I-band light curve. The overall modulation can be described by effects resulting from the presence of a superhump. Comparing our light curve with that reported recently we find evidence for a change in the quiescent base level. Similar changes have now been reported for four soft X-ray transients, implying that they may be a common feature of such systems in quiescence. Furthermore, the maximum in our folded light curve occurs at a different phase than observed before.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2008
- DOI:
- 10.1086/587617
- Bibcode:
- 2008ApJ...680..615J
- Keywords:
-
- accretion;
- accretion disks;
- binaries: close;
- stars: individual: IGR J00291+5934;
- stars: neutron;
- X-rays: binaries