First microlensing candidates from the MEGA survey of M 31

Abstract

Abstract. We present the first M 31 candidate microlensing events from the Microlensing Exploration of the Galaxy and Andromeda (MEGA) survey. MEGA uses several telescopes to detect microlensing towards the nearby Andromeda galaxy, M 31, in order to establish whether massive compact objects are a significant contribution to the mass budget of the dark halo of M 31. The results presented here are based on observations with the Isaac Newton Telescope on La Palma, during the 1999/00 and 2000/01 observing seasons. In this data set, 14 variable sources consistent with microlensing have been detected, 12 of which are new and 2 have been reported previously by the POINT-AGAPE group. A preliminary analysis of the spatial and timescale distributions of the candidate events support their microlensing nature. We compare the spatial distributions of the candidate events and of long-period variable stars, assuming the chances of finding a long-period variable and a microlensing event are comparable. The spatial distribution of our candidate microlensing events is more far/near side asymmetric than expected from the detected long-period variable distribution. The current analysis is preliminary and the asymmetry not highly significant, but the spatial distribution of candidate microlenses is suggestive of the presence of a microlensing halo.

Influence of magnification threshold on pixel lensing optical depth, event rate and time scale distributions towards M 31

“…The main effect of u T (x, y) φ is to decrease the event time scale, in particular towards the inner regions of M 31, giving a larger number of short duration events with respect to expectations based on t c (x, y) calculations. Both for self and dark events the pixel lensing time scale we obtain is 1−7 days, in agreement with results in Kerins (2004), but much shorter with respect to the duration of the events observed by the MEGA Collaboration (de Jong et al 2004). This is most likely due to the fact that current experiments may not detect events shorter than a few days.…”

“…In particular, the MEGA Collaboration (de Jong et al 2004) presented the first 14 M 31 candidate microlensing events, 12 of which are new and 2 that have been reported by the POINT-AGAPE Collaboration (Paulin-Henriksson et al 2003). The preliminary analysis of the spatial and timescale distribution of the events supports their microlensing nature.…”

“…Columns are the model name, the component name, the mass of the component, its central density ρ 0 and the adopted cut-off radius R. Additional columns give, where appropriate, the core radius a, the disk scale length h and height H, the flattening parameter q and the B-band mass-to-light ratio M/L B in solar units. More recently, based on observations with the Isaac Newton Telescope on La Palma (Kerins et al 2001), the MEGA (de Jong et al 2004), POINT-AGAPE (Paulin-Henriksson et al 2003;Calchi Novati et al 2003;Uglesich et al 2004) and WeCAPP (Riffeser et al 2003) collaborations claimed to find evidence of several microlensing events.…”

First microlensing candidate towards M 31 from the Nainital Microlensing Survey

“…The large and variable seeing in our observations further worsens the contamination problem. Most of the pixel lensing candidates towards M 31 are severely contaminated by the nearby red variable stars which is also reflected in the various candidates reported by Calchi Novati et al (2002Novati et al ( , 2003, Paulin-Henriksson et al (2002) andde Jong et al (2003).…”

“…Bonanos et al 2003;Taylor 2004). Recently the MEGA collaboration reported 14 microlensing candidates in their survey towards M 31 using the image subtraction technique (de Jong et al 2003). Two of them (ML-7 and ML-11) had already been reported by POINT-AGAPE in their survey using the pixel technique (PA-99-N2 and PA-00-S4 respectively).…”