POINT-AGAPE pixel lensing survey of M 31

Novati, S. Calchi; Paulin-Henriksson, S.; An, J.; Baillon, P.; Belokurov, V.; Carr, B. J.; Crézé, M.; Evans, N. W.; Giraud‐Héraud, Y.; Gould, Andrew; Hewett, Paul C.; Jetzer, Ph.; Kaplan, J.; Kerins, E.; Smartt, S. J.; Stalin, C. S.; Tsapras, Y.; Weston, Mark

doi:10.1051/0004-6361:20053135

Cited by 84 publications

(47 citation statements)

References 39 publications

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“…Since PAnd-5 is at a location where dust lanes become visible, we also checked the extinction values along the line of sights to the events to find out whether one event could be particularly reddened by M31 dust. We used the dust extinction map of Montalto et al (2009; Our results concerning these long timescale events at 2 and 6 kpc from the Andromeda center are in agreement with previous results: long timescale lensing events have been found by POINT-AGAPE (Calchi Novati et al 2005) at a distance of 22 from M31 (PA-99-N2) with a timescale of 22 days.…”

Section: The First Microlensing Eventssupporting

confidence: 86%

“…The result of the POINT-AGAPE team suggests the existence of MACHOs to explain some of the events (Calchi Novati et al 2005), while the MEGA team claims that the result of their 14 microlensing events (de Jong et al 2006), although two of them are more likely to be supernovae (SNe; Cseresnjes et al 2005), is reconcilable with self-lensing scenario. Few possible issues on the MEGA results have been addressed by the analysis of Ingrosso et al (2006Ingrosso et al ( , 2007.…”

Section: Introductionmentioning

confidence: 99%

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PAndromeda—FIRST RESULTS FROM THE HIGH-CADENCE MONITORING OF M31 WITH Pan-STARRS 1

Lee¹,

Riffeser²,

Koppenhoefer³

et al. 2012

The Astronomical Journal

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The Pan-STARRS 1 (PS1) survey of M31 (PAndromeda) is designed to identify gravitational microlensing events, caused by bulge and disk stars (self-lensing) and by compact matter in the halos of M31 and the Milky Way (halo lensing or lensing by massive compact halo objects). With the 7 deg 2 field of view (FOV) of PS1, the entire disk of M31 can be imaged with one single pointing. Our aim is to monitor M31 with this wide FOV with daily sampling (20 minutes day −1 ). In the 2010 season, we acquired in total 91 nights toward M31, with 90 nights in the r P1 and 66 nights in the i P1 . The total integration time in r P1 and i P1 are 70,740 s and 36,180 s, respectively. As a preliminary analysis, we study a 40 × 40 sub-field in the central region of M31, a 20 × 20 sub-field in the disk of M31, and a 20 × 20 sub-field for the investigation of astrometric precision. We demonstrate that the point-spread function is good enough to detect microlensing events. We present light curves for six candidate microlensing events. This is a competitive rate compared with previous M31 microlensing surveys. Finally, we also present one example light curve for Cepheids, novae, and eclipsing binaries in these sub-fields.

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Section: The First Microlensing Eventssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

PAndromeda—FIRST RESULTS FROM THE HIGH-CADENCE MONITORING OF M31 WITH Pan-STARRS 1

Lee¹,

Riffeser²,

Koppenhoefer³

et al. 2012

The Astronomical Journal

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“…The NE shelf lies closer to us than the disc of M31, and partially overlaps with it. This may have relevance to microlensing surveys which aim to detect compact objects of stellar type mass (de Jong et al 2004; Calchi Novati et al 2005), since the lensing event probability will be boosted relative to disc self‐lensing by the gap in distance between the disc and NE shelf, and by the large relative velocities between the disc and shelf stars.…”

Section: Discussionmentioning

confidence: 99%

Investigating the Andromeda stream - III. A young shell system in M31

Fardal

Guhathakurta

Babul

et al. 2007

Monthly Notices of the Royal Astronomical Society

128

258

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Published maps of red giant stars in the halo region of M31 exhibit a giant stellar stream to the south of this galaxy, as well as a giant ‘shelf’ to the northeast of M31's centre. Using these maps, we find that there is a fainter shelf of comparable size on the western side as well. By choosing appropriate structural and orbital parameters for an accreting dwarf satellite within the accurate M31 potential model of Geehan et al., we produce a very similar structure in an N‐body simulation. In this scenario, the tidal stream produced at pericentre of the satellite's orbit matches the observed southern stream, while the forward continuation of this tidal stream makes up two orbital loops, broadened into fan‐like structures by successive pericentric passages; these loops correspond to the north‐eastern and western shelves. The tidal debris from the satellite also reproduces a previously observed ‘stream’ of counterrotating planetary nebulae and a related stream seen in red giant stars. The debris pattern in our simulation resembles the shell systems detected around many elliptical galaxies, though this is the first identification of a shell system in a spiral galaxy and the first in any galaxy close enough to allow measurements of stellar velocities and relative distances. We discuss the physics of these partial shells, highlighting the role played by spatial and velocity caustics in the observations. We show that kinematic surveys of the tidal debris will provide a sensitive measurement of M31's halo potential, while quantifying the surface density of debris in the shelves will let us reconstruct the original mass and time of disruption of the progenitor satellite.

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“…Perhaps because of this, the independent calculations of the optical depth of the M31 halo currently in the literature are contradictory. Calchi Novati et al (2005) found six short‐duration events and argued that at least 20 per cent of the M31 halo is in the form of dark, compact objects. De Jong et al (2006) identified 14 events, but concluded that the signal was equally consistent with both self‐lensing and with dark, compact halo objects.…”

Section: Discussionmentioning

confidence: 99%

The microlensing optical depth towards the Large Magellanic Cloud: is there a puzzle?

Evans

Belokurov

2007

Monthly Notices of the Royal Astronomical Society

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Using neural networks, Belokurov, Evans & Le Du showed that seven out of the 29 microlensing candidates towards the Large Magellanic Cloud (LMC) of the MACHO collaboration are consistent with blended microlensing and added Gaussian noise. We then estimated the microlensing optical depth to the LMC to be 0.3 × 10−7≲τ≲ 0.5 × 10−7, lower than the value τ= 1.2+0.4−0.3× 10−7 claimed by the MACHO collaboration. There have been independent claims of a low optical depth to the LMC by the EROS collaboration, who have most recently reported τ < 0.36 × 10−7. Griest & Thomas have contested our calculations. Unfortunately, their paper contains a number of scientific misrepresentations of our work, which we clarify here. We stand by our application of the neural networks to microlensing searches, and believe it to be a technique of great promise. Rather, the main cause of the disparity between Griest & Thomas and Belokurov et al. lies in the very different data sets through which these investigators look for microlensing events. Whilst not everything is understood about the microlensing data sets towards the LMC, the latest downward revisions of the optical depth to (1.0 ± 0.3) × 10−7 is within ≲2σ of the theoretical prediction from stellar populations alone. Efficiency calculations can correct for the effects of false negatives, but they cannot correct for the effects of false positives (variable stars that are mistaken for microlensing). In our opinion, the best strategy in a microlensing experiment is to eschew a decision boundary altogether and so sidestep the vagaries of candidate selection and efficiency calculations. Rather, each lightcurve should be assigned a probability that it is a bona fide microlensing event and the microlensing rate calculated by summing over the probabilities of all such lightcurves.

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POINT-AGAPE pixel lensing survey of M 31

Cited by 84 publications

References 39 publications

PAndromeda—FIRST RESULTS FROM THE HIGH-CADENCE MONITORING OF M31 WITH Pan-STARRS 1

PAndromeda—FIRST RESULTS FROM THE HIGH-CADENCE MONITORING OF M31 WITH Pan-STARRS 1

Investigating the Andromeda stream - III. A young shell system in M31

The microlensing optical depth towards the Large Magellanic Cloud: is there a puzzle?

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