First microlensing candidate towards M 31 from the Nainital Microlensing Survey

Abstract

We report our first microlensing candidate NMS-E1 towards M 31 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 M 31 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 M 31 at α= 0^b43^m33^δ3 and δ=+41° 06'44", about 15.5 arcmin to the South-East direction of the center of M 31. The degenerate Paczynski 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) _O~1.1mag. The microlensing candidate is blended by red variable stars; consequently the light curves do not strictly follow the characteristic Paczynski shape and achromatic nature. However its long period monitoring and similar behaviour in R and I bands supports its microlensing nature.