Optical and X–ray Observations of Igr J00291+5934 in Quiescence

We report on optical and X–ray observations of the accretion powered ms 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 erg cm s 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 lightcurve with that reported recently we find evidence for a change in the quiescent base level. Similar changes have now been reported for 4 soft X–ray transients implying that they may be a common feature of such systems in quiescence. Furthermore, the maximum in our folded lightcurve occurs at a different phase than observed before. Subject headings: stars: individual (IGR J00291+5934) — accretion: accretion discs — binaries: close — stars: neutron — X-rays: binaries