First microlensing candidate towards M31 from the Nainital Microlensing Survey

We report our first microlensing candidate NMS-E1 towards M31 from the data accumulated during the four years of Nainital Microlensing Survey. Cousin R and I band observations of ∼ 13 ′ × 13 ′ field in the direction of M31 have been carried out since 1998 and data is analysed using the pixel technique proposed by the AGAPE collaboration. NMS-E1 lies in the disk of M31 at α = 04333.3 and δ = +41◦06 ′ 44 ′′ , about 15.5 arcmin to the South-East direction of the center of M31. The degenerate Paczyński fit gives a half intensity duration of ∼ 59 days. The photometric analysis of the candidate shows that it reached R ∼ 20.1 mag at the time of maximum brightness and the colour of the source star was estimated to be (R − I)0 ∼ 1.1 mag. The microlensing candidate is blended by red variable stars; consequently the light curves do not strictly follow the characteristic Paczyński shape and achromatic nature. However its long period monitoring and similar behaviour in R and I bands supports its microlensing nature.