The POINT-AGAPE survey: 4 high signal-to-noise microlensing candidates detected towards M 31

Paulin-Henriksson, S.; Baillon, P.; Bouquet, A.; Carr, B. J.; Crézé, M.; Evans, N. W.; Giraud‐Héraud, Y.; Gould, Andrew; Hewett, Paul C.; Kaplan, J.; Kerins, E.; Du, Y. Le; Melchior, A. L.; Smartt, S. J.; Valls–Gabaud, D.

doi:10.1051/0004-6361:20030519

Cited by 65 publications

(100 citation statements)

References 18 publications

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“…The MEGA collaboration (de Jong et al 2004) has reported the detection of 14 candidate events towards M 31 by using Isaac Newton Telescope (INT) data. Two of these events have been previously reported by the POINT-AGAPE collaboration (Paulin-Henriksson et al 2003), which recently has presented a high-threshold analysis of the full 3 years data set (Calchi Novati et al 2005). This analysis shows that the observed signal is much larger than expect from self-lensing alone and that some fraction of the halo mass must be in form of MACHOs.…”

Section: Introductionmentioning

confidence: 91%

Monte Carlo analysis of MEGA microlensing events towards M 31

Ingrosso

Novati

Paolis

et al. 2005

A&A

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We perform an analytical study and a Monte Carlo (MC) analysis of the main features for microlensing events in pixel lensing observations towards M 31. Our main aim is to investigate the lens nature and location of the 14 candidate events found by the MEGA collaboration. Assuming a reference model for the mass distribution in M 31 and the standard model for our galaxy, we estimate the MACHO-to-self lensing probability and the event time duration towards M 31. Reproducing the MEGA observing conditions, as a result we get the MC event number density distribution as a function of the event full-width half-maximum duration t 1/2 and the magnitude at maximum R max . For a MACHO mass of 0.5 M we find typical values of t 1/2 20 day and R max 22, for both MACHO-lensing and self-lensing events occurring beyond about 10 arcmin from the M 31 center. A comparison of the observed features (t 1/2 and R max ) with our MC results shows that for a MACHO mass > 0.1 M the four innermost MEGA events are most likely self-lensing events, whereas the six outermost events must be genuine MACHO-lensing events.

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Section: Introductionmentioning

confidence: 91%

Monte Carlo analysis of MEGA microlensing events towards M 31

Ingrosso

Novati

Paolis

et al. 2005

A&A

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“…Hence, high quality data (e.g. Paulin-Henriksson et al 2003) or detection of the source star (e.g. Aurière et al 2001) are required to accurately determine the t E and hence the mass of the MACHO.…”

Section: Pixel Methodsmentioning

confidence: 99%

“…We do not enforce any selection criteria on t 1/2 as performed in some other surveys (e.g. Paulin-Henriksson et al 2003;Riffeser et al 2003) because of: a) observational gaps in our data of up to 10 days between two consecutive nights within a single observing season; b) the duration of the observations per season with an average observing density of once in three days; c) the total period of our monitoring (>800 days) that is large enough to exclude any other kind of variability; and d) we are observing towards the outer disk of M 31 where one generally expects long time scale events. Since the concentration of variable stars having longer …”

Section: Selection Criteriamentioning

confidence: 99%

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First microlensing candidate towards M 31 from the Nainital Microlensing Survey

Joshi

Pandey

Narasimha

et al. 2005

A&A

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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 h 43 m 33. s 3 and δ = +41 • 06 44 , about 15.5 arcmin to the South-East direction of the center of M 31. 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.

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“…This study will be done in a forthcoming paper (De Paolis et al 2004) with the aim of investigating the lens nature (i.e. the population to which the lens belongs) for the events discovered by MEGA (de Jong et al 2004) and POINT-AGAPE (Paulin-Henriksson et al 2003).…”

Section: Introductionmentioning

confidence: 99%

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

Paolis¹,

Ingrosso²,

Nucita³

2005

A&A

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Abstract. Pixel lensing is the gravitational microlensing of light from unresolved stars contributing to the luminosity flux collected by a single pixel. A star must be sufficiently magnified, that is, the lens impact parameter must be less than a threshold value u T if the excess photon flux in a pixel is to be detected over the background. Assuming the parameters of the Isaac Newton Telescope and typical observing conditions, we present maps in the sky plane towards M 31 of threshold impact parameter, optical depth, event number and event time scale, analyzing in particular how these quantities depend on u T in pixel lensing searches. We use an analytical approach consisting of averaging on u T and the star column density the optical depth, microlensing rate and event duration time scale. An overall decrease in the expected optical depth and event number with respect to the classical microlensing results is found, particularly towards the high luminosity M 31 inner regions. As expected, pixel lensing events towards the inner region of M 31 are mostly due to self-lensing, while in the outer region dark events dominate even for a 20% MACHO halo fraction. We also find a far-disk/near-disk asymmetry in the expected event number, smaller than that found by Kerins (2004). Both for self and dark lensing events, the pixel lensing time scale we obtain is 1−7 days, dark events lasting roughly twice as long as self-lensing events. The shortest events are found to occur towards the M 31 South Semisphere. We also note that the pixel lensing results depend on u T and u 2 T values and ultimately on the observing conditions and telescope capabilities.

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The POINT-AGAPE survey: 4 high signal-to-noise microlensing candidates detected towards M 31

Cited by 65 publications

References 18 publications

Monte Carlo analysis of MEGA microlensing events towards M 31

Monte Carlo analysis of MEGA microlensing events towards M 31

First microlensing candidate towards M 31 from the Nainital Microlensing Survey

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

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