New outburst from the X-ray pulsar RX J0440.9+4431 and discovery of a possible ~155 days orbital period

On the basis of recent SWIFT/BAT observations we report a detection of the third consequent outburst from the X-ray pulsar RX J0440.9+4431, which was started on 2011-01-29. The persistent X-ray source RX J0440.9+4431 has been found during the ROSAT Galactic plane survey with the optical companion of BSD 24-491 / LS V +44 17) classified as a Be star (Motch et al., A&A, 323, 853, 1997). Later Reig, Roche (MNRAS, 306, 100, 1999) detected X-ray pulsations from this source with the period of ~202.5 s.