AgapeZ1: a large amplification microlensing event or an odd variable star towards the inner bulge of M31
Giraud-Héraud, Y.; Bouquet, A.; Soucail, G.; Aurière, M.; Moniez, M.; Ansari, R.; Baillon, P.; Coupinot, G.; Coutures, Ch.; Ghesquière, C.; Gondolo, P.; Hecquet, J.; Kaplan, J.; Kim, A.; Le Du, Y.; Melchior, A. L.; Picat, J. P.
France, Switzerland, Germany, United Kingdom
Abstract
AgapeZ1 is the brightest and the shortest duration microlensing candidate event found to date in the Agape experiment. It occurred only 42'' from the centre of M31 at RA=0(h) 42(m) 41.47(s) and Dec=41(deg) 16' 39.1'' (J2000). Our photometry shows that the half intensity duration of the event is 5.3 days and at maximum brightness its magnitude is R = 17.9 (M_R ~ -6) with B-R=0.80 mag colour. A search on HST archives produced a single resolved star within the projected event position error box. Its magnitude is R=22, and its colour is compatible with that of the event at the 2 sigma level. If this event is identified with the HST star, the implied amplification is about 4 magnitudes or 40 in brightness. This would lead to an Einstein crossing time radius of about 60 days. AgapeZ1 could be a bulge/bulge microlensing event involving a binary star. The photometric properties of the object are inconsistent with classical M31 variable stars such as Miras, classical novae, dwarf-novae, and bumpers. However, we cannot rule out the possibility that AgapeZ1 is in fact an odd variable star. Based on data collected with the 2\,m Bernard Lyot Telescope (TBL) operated by INSU-CNRS and Pic-du-Midi Observatory (USR 5026). \protect\newline The experiment was funded by IN2P3 and INSU of CNRS