We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find six events that exhibit very strong microlensing parallax signals due, in part, to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distances and masses of the lens objects based on a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are greater than 1 M , which suggests that a substantial fraction of the Galactic lenses may be massive stellar remnants. This could explain the observed excess of long-timescale microlensing events. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M=M ¼ 6 þ10 À3 and M=M ¼ 6 þ7 À3 , respectively. The observed upper limits on the absolute brightness of main-sequence stars for these lenses are less than 1 L , so both lenses are black hole candidates. The black hole interpretation is also favored by a likelihood analysis with a Bayesian prior using a conventional model for the lens mass function. We consider the possibility that the source stars for some of these six events may lie in the foreground Galactic disk or in the Sagittarius (Sgr) dwarf galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future Hubble Space Telescope observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by the Space Interferometry Mission or the Keck or VLT interferometers, as explained by Delplancke, Gó rski, & Richichi, will allow direct measurements of the lens masses for stellar remnant lenses as well.

We present the lightcurves of 21 gravitational microlensing events from the first six years of the MACHO Project gravitational microlensing survey which are likely examples of lensing by binary systems. These events were manually selected from a total sample of ~350 candidate microlensing events which were either detected by the MACHO Alert System or discovered through retrospective analyses of the MACHO database. At least 14 of these 21 events exhibit strong (caustic) features, and 4 of the events are well fit with lensing by large mass ratio (brown dwarf or planetary) systems, although these fits are not necessarily unique. The total binary event rate is roughly consistent with predictions based upon our knowledge of the properties of binary stars, but a precise comparison cannot be made without a determination of our binary lens event detection efficiency. Towards the Galactic bulge, we find a ratio of caustic crossing to non-caustic crossing binary lensing events of 12:4, excluding one event for which we present 2 fits. This suggests significant incompleteness in our ability to detect and characterize non-caustic crossing binary lensing. The distribution of mass ratios, N(q), for these binary lenses appears relatively flat. We are also able to reliably measure source-face crossing times in 4 of the bulge caustic crossing events, and recover from them a distribution of lens proper motions, masses, and distances consistent with a population of Galactic bulge lenses at a distance of 7 +/- 1 kpc. This analysis yields 2 systems with companions of ~0.05 M_sun.Comment: 83 pages, including 5 tables and 48 figures; submitted to The Astrophysical Journal. Data will soon be available at http://wwwmacho.mcmaster.ca/ and http://wwwmacho.anu.edu.au

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

We present observations of the microlensing event MACHO 98-BLG-35, which reached a peak magniÐcation factor of almost 80. These observations by the Microlensing Planet Search (MPS) and MOA collaborations place strong constraints on the possible planetary system of the lens star and show intriguing evidence for a low-mass planet with a mass fraction 4 ] 10~5 ¹ v ¹ 2 ] 10~4. A giant planet with v \ 10~3 is excluded from 95% of the region between 0.4 and 2.5 from the lens star, where is R E R E the Einstein ring radius of the lens. This exclusion region is more extensive than the generic "" lensing zone,ÏÏ which is 0.6È1.6For smaller mass planets, we can exclude 57% of the "" lensing zone ÏÏ for R E . v \ 10~4 and 14% of the lensing zone for v \ 10~5. The mass fraction v \ 10~5 corresponds to an Earth-mass planet for a lensing star of mass D0.3A number of similar events will provide sta-M _ . tistically signiÐcant constraints on the prevalence of Earth-mass planets. In order to put our limits in more familiar terms, we have compared our results to those expected for a solar system clone, averaging over possible lens system distances and orientations. We Ðnd that such a system is ruled out at the 90% conÐdence level. A copy of the solar system with Jupiter replaced by a second Saturn-mass planet can be ruled out at 70% conÐdence. Our low-mass planetary signal (few Earth masses to Neptune mass) is signiÐcant at the 4.5 p conÐdence level. If this planetary interpretation is correct, the MACHO 98-BLG-35 lens system constitutes the Ðrst detection of a low-mass planet orbiting an ordinary star without gas giant planets.20

We present the observations of the binary lensing event MACHO-98-SMC-1 conducted at the Mt. Stromlo 74" telescope by the Microlensing Planet Search (MPS) collaboration. The MPS data constrain the first caustic crossing to have occurred after 1998 June 5.55 UT and thus directly rule out one of the two fits presented by the PLANET collaboration (model II). This substantially reduces the uncertainty in the the relative proper motion estimations of the lens object.We perform joint binary microlensing fits of the MPS data together with the publicly available data from the EROS, MACHO/GMAN and OGLE collaborations. We also study the binary lens fit parameters previously published by the PLANET and MACHO/GMAN collaborations by using them as initial values for χ 2 minimization. Fits based on the PLANET model I appear to be in conflict with the GMAN-CTIO data. From our best fit, we find that the lens system has a proper motion of µ = 1.3 ± 0.2 km s −1 kpc −1 with respect to the source, which implies that the lens system is most likely to be located in the Small Magellanic Cloud strengthening the conclusion of previous reports.

Aims. We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ∼ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Methods. Both finite-source and parallax effects permit a measurement of the angular Einstein radius θ E = 0.48 ± 0.01 mas and the parallax π E = 0.12 ± 0.03, leading to an estimate of the lens mass M = 0.50 ± 0.14 M and its distance to the observer D L = 5.5 ± 0.4 kpc. This is only the second determination of a reasonably precise (<30%) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units (r ⊥ , m p ), where r ⊥ is the projected planet-star separation and m p is the planet mass. Results. When computing planet detection efficiency, we did not find any planetary signature, i.e. none of the planetary configurations provides a Δχ 2 improvement higher than 60, and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6-10] and [1.4-4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8-3.1] AU.

We cross-correlate the cosmic microwave background (CMB) temperature anisotropy maps from the Wilkinson Microwave Anisotropy Probe (WMAP), MAXIMA-1, and MAXIMA-2 experiments. We use the cross spectrum, which is the spherical harmonic transform of the angular two-point correlation function, to quantify the correlation as a function of angular scale. We find that the three possible pairs of cross spectra are in close agreement with each other and with the power spectra of the individual maps. The probability that there is no correlation between the maps is smaller than 1 ; 10 À8 . We also calculate power spectra for maps made of differences between pairs of maps and show that they are consistent with no signal. The results conclusively show that the three experiments not only display the same statistical properties of the CMB anisotropy, but also detect the same features wherever the observed sky areas overlap. We conclude that the contribution of systematic errors to these maps is negligible and that MAXIMA and WMAP have accurately mapped the CMB anisotropy.

We describe the Millimeter wave Anisotropy eXperiment IMaging Array ͑MAXIMA͒, a balloon-borne experiment which measured the temperature anisotropy of the cosmic microwave background ͑CMB͒ on angular scales of 10Ј to 5°. MAXIMA mapped the CMB using 16 bolometric detectors in spectral bands centered at 150, 240, and 410 GHz, with 10Ј resolution at all frequencies.The combined receiver sensitivity to CMB anisotropy was ϳ40 K ͱ s. The bolometric detectors, which were cooled to 100 mK, were a prototype of the detectors which will be used on the Planck Surveyor Satellite of the European Space Agency. Systematic parasitic contributions were controlled by using four uncorrelated spatial modulations, thorough cross-linking, multiple independent CMB observations, heavily baffled optics, and strong spectral discrimination. Pointing reconstruction was accurate to 1Ј, and absolute calibration was better than 4%. Two MAXIMA flights with more than 8.5 h of CMB observations have mapped a total of 300 deg 2 of the sky in regions of negligible known foreground emission. MAXIMA results have been released in previous publications and shown to be consistent with the Wilkinson Microwave Anisotropy Probe. MAXIMA I maps, power spectra, and correlation matrices are publicly available at http://cosmology.berkeley.edu/maxima.