[Show abstract][Hide abstract] ABSTRACT: We investigate the influence of the matter along the line of sight and in the
lens environment on the image configurations, relative time delays, and the
resulting models of strong gravitational lensing. The distribution of matter in
space and properties of gravitationally bound haloes are based on the
Millennium Simulation. In our numerical experiments we consider isolated lens
in a uniform universe model and the same lens surrounded by close neighbours
and/or objects close to the line of sight which gives four different
descriptions of the light propagation. We compare the results of the lens
modeling which neglects effects of the environment and line of sight, when
applied to image configurations resulting from approaches partially or fully
taking into account these effects. We show that for a source at the redshift
z=2 the effects are indeed important and may prevent successful fitting of lens
models in a substantial part of simulated image configurations, especially when
the relative time delays are taken into account. To have good constraints on
the models we limit ourselves to configurations of four images. We consider
eighty lenses and large number of source positions in each case. The influence
of the lens neighbourhood and the line of sight introduces the spread into the
fitted values of the deflection angles which translates into the spread in the
lens velocity dispersion of 4 per cent. Similarly for the lens axis ratio we
get the spread of 10 per cent and for the Hubble's constant of 6 per cent. When
averaged over all lenses and all image configurations considered, the median
fitted values of the parameters (including the Hubble's constant) do not differ
more than 1 per cent from their values used in simulations.
Preview · Article · Jan 2014 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We make use of publicly available results from N-body Millennium Simulation
to create mock samples of lensed supernovae type Ia and core-collapse.
Simulating galaxy-galaxy lensing we derive the rates of lensed supernovae and
find than at redshifts higher that 0.5 about 0.06 per cent of supernovae will
be lensed by a factor two or more. Future wide field surveys like Gaia or LSST
should be able to detect lensed supernovae in their unbiased sky monitoring.
Gaia (from 2013) will detect at least 2 cases whereas LSST (from 2018) will see
more than 500 a year. Large number of future lensed supernovae will allow to
verify results of cosmological simulations. The strong galaxy- galaxy lensing
gives an opportunity to reach high-redshift supernovae type Ia and extend the
Hubble diagram sample.
Full-text · Article · Dec 2012 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We investigate strong lensing by non-singular finite isothermal ellipsoids
taking into account the influence of the matter along the line of sight and in
the close lens vicinity. We compare three descriptions of light propagation:
the full approach taking into account all matter inhomogeneities along the
rays, the single plane approach, where we take into account the influence of
the strong lens neighbours but neglect the foreground and background objects,
and the single lens approach. In each case we simulate many strong lensing
configurations placing a point source at the same redshift but in different
locations inside the region surrounded by caustics. We further analyze
configurations of four or five images. For every simulated strong lensing
configuration we attempt to fit a simplified lens model using a single
isothermal ellipsoid or a single isothermal ellipsoid with external shear. The
single lens fits to configurations obtained in the full approach are rejected
in majority of cases with 95% significance. For configurations obtained in the
single plane approach the rejection rate is substantially lower. Also the
inclusion of external shear in simplified modeling improves the chances of
obtaining acceptable fits, but the problem is not solved completely. The
quantitative estimates of the rates of rejection of simplified models depend on
the required accuracy of the models, and we present few illustrative examples,
which show that both matter close to the lens and matter along the rays do have
important influence on lens modeling. We also estimate the typical value of the
external shear and compare the fitted parameters of the simplified models with
the parameters of the lenses used in the simulations.
Preview · Article · Apr 2012 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We report the result of the analysis of the light curve of a caustic-crossing
binary-lens microlensing event OGLE-2009-BLG-023/MOA-2009-BLG-028. Even though
the event was observed solely by survey experiments, we could uniquely
determine the mass of the lens and distance to it by simultaneously measuring
the Einstein radius and lens parallax. From this, we find that the lens system
is composed of M-type dwarfs with masses $(0.50\pm 0.07) \ M_\odot$ and
$(0.15\pm 0.02)\ M_\odot$ located in the Galactic disk with a distance of $\sim
1.8$ kpc toward the Galactic bulge direction. The event demonstrates that
physical lens parameters of binary-lens events can be routinely determined from
future high-cadence lensing surveys and thus microlensing can provide a new way
to study Galactic binaries.
Full-text · Article · Apr 2011 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We present 27 binary lens candidates from OGLE-III Early Warning System database for the seasons 2006-2008. The candidates have been selected by visual light curves inspection. Our sample of binary lens events consists now of 78 stellar systems and 7 extrasolar planets of OGLE-III published elsewhere. Examining the distribution of stellar binaries we find that the number of systems per logarithmic mass ratio interval increases with mass ratio q, in contradiction with our previous findings. Stellar binaries belong to the region 0.03
Full-text · Article · Jan 2010 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We employ a hybrid method of modeling matter distribution in space based on the Millennium Simulation, using a coarse grid averaged matter density distribution with overlaid population of gravitationally bound halos. Using Born approximation we simulate the light propagation in such inhomogeneous cosmological model, obtaining shear maps for five ≈3°×3° fields at several redshifts. We analyze the influence of halos and background mass density on the tangential shear component. We show the presence of a weak signal at large separations caused by the large scale structure in matter distribution. We also investigate the relation between the shear peaks and the distribution of halo masses in their foregrounds, obtaining the dependence of mass spectra on the shear value. As other studies show, the top peaks of the shear are always related to the presence of very massive halos (galaxy clusters), but we find that their expected mass decreases with the increasing redshift of a map and with the increasing angular scale of its smoothing.
No preview · Article · Jan 2010 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include photometric and astrometric measurements from the Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve, such as microlens parallax, planetary orbital motion, and finite-source effects. Our primary analysis leads to the conclusion that the host of Jovian planet OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M = 0.46 ± 0.04 Msun, distance Dl = 3.2 ± 0.4 kpc, and thick-disk kinematics vLSR ~ 103 km s-1. From the best-fit model, the planet has mass Mp = 3.8 ± 0.4 MJupiter, lies at a projected separation r⊥ = 3.6 ± 0.2AU from its host, and so has an equilibrium temperature of T ~ 55 K, that is, similar to Neptune. A degenerate model gives similar planetary mass Mp = 3.4 ± 0.4 MJupiter with a smaller projected separation, r⊥ = 2.1 ± 0.1AU, and higher equilibrium temperature, T ~ 71 K. These results from the primary analysis suggest that OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that is hosted by an M dwarf. However, the formation of such high-mass planetary companions in the outer regions of M dwarf planetary systems is predicted to be unlikely within the core-accretion scenario. There are a number of caveats to this primary analysis, which assumes (based on real but limited evidence) that the unlensed light coincident with the source is actually due to the lens, that is, the planetary host. However, these caveats could mostly be resolved by a single astrometric measurement a few years after the event.
Full-text · Article · Jul 2009 · The Astrophysical Journal
[Show abstract][Hide abstract] ABSTRACT: A microlensing event may exhibit a second brightening when the source and/or the lens is a binary star. Previous study revealed 19 such repeating event candidates among 4120 investigated microlensing light curves of the Optical Gravitational Lensing Experiment (OGLE). The same study gave the probability ~ 0.0027 for a repeating event caused by a binary lens. We present the simulations of binary source lensing events and calculate the probability of observing a second brightening in the light curve. Applying to simulated light curves the same algorithm as was used in the analysis of real OGLE data, we find the probability ~ 0.0018 of observing a second brightening in a binary source lensing curve. The expected and measured numbers of repeating events are in agreement only if one postulates that all lenses and all sources are binary. Since the fraction of binaries is believed to be <= 50%, there seems to be a discrepancy.
Preview · Article · Feb 2009 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We present observations of the unusual microlensing event OGLE 2003-BLG-235/MOA 2003-BLG-53. In this event, a short-duration (~7 days) low-amplitude deviation in the light curve due to a single-lens profile was observed in both the MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment) survey observations. We find that the observed features of the light curve can only be reproduced using a binary microlensing model with an extreme (planetary) mass ratio of 0.0039 for the lensing system. If the lens system comprises a main-sequence primary, we infer that the secondary is a planet of about 1.5 Jupiter masses with an orbital radius of ~3 AU.
Full-text · Article · Dec 2008 · The Astrophysical Journal
[Show abstract][Hide abstract] ABSTRACT: Microlensing events are usually selected among single-peaked non-repeating light curves in order to avoid confusion with variable stars. However, a microlensing event may exhibit a second microlensing brightening episode when the source or/and the lens is a binary system. A careful analysis of these repeating events provides an independent way to study the statistics of wide binary stars and to detect extrasolar planets. Previous theoretical studies predicted that 0.5 - 2 % of events should repeat due to wide binary lenses. We present a systematic search for such events in about 4000 light curves of microlensing candidates detected by the Optical Gravitational Lensing Experiment (OGLE) towards the Galactic Bulge from 1992 to 2007. The search reveals a total of 19 repeating candidates, with 6 clearly due to a wide binary lens. As a by-product we find that 64 events (~2% of the total OGLE-III sample) have been miss-classified as microlensing; these miss-classified events are mostly nova or other types of eruptive stars. The number and importance of repeating events will increase considerably when the next-generation wide-field microlensing experiments become fully operational in the future. Comment: 11 pages, 4 figures (+ appendix A) and 3 tables
Full-text · Article · Nov 2008 · Monthly Notices of the Royal Astronomical Society
[Show abstract][Hide abstract] ABSTRACT: We present nine new binary lens candidates from OGLE-III Early Warning System database for the season of 2005. We have also found four events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses in our previous studies (10 caustic crossing events of OGLE-II seasons 1997--1999 and 34 binary lens events of OGLE-III seasons 2002--2004, including one planetary event), in this work and in three publications concerning planetary events of season 2005, we find four cases of extreme mass ratio binaries (q<0.01), and almost all other models with mass ratios in the range 0.1<q<1.0, which may indicate the division between planetary systems and binary stars. Comment: 19 pages, 45 figures
Full-text · Article · Feb 2008 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We present 19 binary lens candidates from OGLE-III Early Warning System database for the season of 2004. We have also found five events interpreted as single mass lensing of double sources. The candidates have been selected by visual light curves inspection. Examining the models of binary lenses of this and our previous studies (10 caustic crossing events of OGLE-II seasons 1997--1999 and 15 binary lens events of OGLE-III seasons 2002--2003) we find one case of extreme mass ratio binary (q ~ 0.005, a known planetary lens OGLE 2003-BLG-235/MOA 2003-BLG-53) and almost all other models with mass ratios in the range 0.1<q<1.0, which may indicate the division between planetary systems and binary stars.
Full-text · Article · Mar 2007 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: Using Monte Carlo simulations we produce several microlensing
amplification maps for each of the four images of the quasar QSO
2237+0305. With FFT algorithms we convolve the maps with the filters
representing sources of different sizes and surface brightness
distributions. The cuts of the convolved maps represent fragments of
synthetic light curves for corresponding sources. Since FFT method is
not time consuming we can examine large number of cases and obtain
several statistical characteristics of image variability. A simple test
involving the measured amplitude of the apparent QSO variability during
approx 5 years of OGLEIII observations gives an estimate of the relative
source velocity, 4000+/-2000 km/s.
Preview · Article · May 2006 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We report the identification of a new cataclysmic variable (denoted as CV2) and a probable microlensing event in the field of the globular cluster M22. Two outbursts were observed for CV2. During one of them superhumps with P_sh=0.08875 d were present in the light curve. CV2 has an X-ray counterpart detected by XMM-Newton. A very likely microlensing event at a radius of 2.3 arcmin from the cluster center was detected. It had an amplitude of Delta_V=0.75 mag and a characteristic time of 15.9 days. Based on model considerations we show that the most likely configuration has the source in the Galactic bulge with the lens in the cluster. Two outbursts were observed for the already known dwarf nova CV1.
Preview · Article · Oct 2005 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We model binary microlensing events OGLE 2003-BLG-170, 267, and 291. Source angular sizes are measured for the events 267 and 291. Model fits to the light curves give parallaxes for the events 267 and 291, and relative source sizes for 170 and 267. Selfconsistency arguments provide extra limits on the models of the event 291. As a result we obtain likelihood estimate of the lens mass for the event 170, mass measurement based on angular size and parallax for 267, and narrow limits on mass in the case of 291. Brown dwarfs are most likely candidates for some of the lens components. The influence of the binary lens rotation and the Earth parallax may be important but hard to distinguish when modeling relatively short lasting binary lens events.
Full-text · Article · Aug 2005 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We report the discovery of a several-Jupiter mass planetary companion to the primary lens star in microlensing event OGLE-2005-BLG-071. Precise (<1%) photometry at the peak of the event yields an extremely high signal-to-noise ratio detection of a deviation from the light curve expected from an isolated lens. The planetary character of this deviation is easily and unambiguously discernible from the gross features of the light curve. Detailed modeling yields a tightly-constrained planet-star mass ratio of q=m_p/M=0.0071+/-0.0003. This is the second robust detection of a planet with microlensing, demonstrating that the technique itself is viable and that planets are not rare in the systems probed by microlensing, which typically lie several kpc toward the Galactic center. Comment: 4 pages. Minor changes. Accepted for publication in ApJ Letters
Full-text · Article · May 2005 · The Astrophysical Journal Letters
[Show abstract][Hide abstract] ABSTRACT: We present observations of the unusual microlensing event OGLE 2003--BLG-- 235/MOA 2003--BLG--53. In this event a short duration ( 7 days) low amplitude deviation in the light curve due a single lens profile was observed in both the MOA and OGLE survey observations. We find that the observed features of the light curve can only be reproduced using a binary microlensing model with an extreme (planetary) mass ratio of for the lensing system. If the lens system comprises a main Institute for Astronomy, University of Edinburgh, Edinburgh, EH9 3HJ, UK; firstname.lastname@example.org Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland; udalski, mj, soszynsk, wyrzykow, msz, mk, szewczyk, zebrun, pietrzyn @astrouw.edu.pl 3 Department of Physics, University of Auckland, Auckland, New Zealand; email@example.com, firstname.lastname@example.org, email@example.com 4 Department of Astrophysical Sciences, Princeton University, Princeton NJ 08544, USA; bp, sumi @astro.princeton.edu 5 Universidad de Concepcion, Departmento de Fisica, Casilla 160-C, Concepcion, Chile 6 Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan; abe, sada, furuta, kkamiya, kurata, kmasuda, ymatsu, muraki, sako, sekiguchi @stelab.nagoya-u.ac.jp 7 Department of Physics, Notre Dame University, Notre Dame, IN 46556, USA; firstname.lastname@example.org 8 Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand; john.hearnshaw, pam.kilmartin @canterbury.ac.nz 9 National Astronomical Observatory of Japan, Tokyo, Japan; email@example.com 10 School of Chemical and Physical Sciences, Victoria University, PO Box 600, Wellington, New Zealand; denis. firstname.lastname@example.org...
[Show abstract][Hide abstract] ABSTRACT: We present 15 binary lens candidates from OGLE-III Early Warning System database for seasons 2002-2003. We also found 15 events interpreted as single mass lensing of double sources. The candidates were selected by visual light curves inspection. Examining the models of binary lenses of this and our previous study (10 caustic crossing events of OGLE-II seasons 1997-1999) we find one case of extreme mass ratio binary (q ≈ 0.005) and the rest in the range 0.1 < q < 1.0, which may indicate the division between planetary systems and binary stars. There is no strong discrepancy between the expected and the observed distributions of mass ratios and separations for binary stars.
Full-text · Article · Jan 2004 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: The microlensing event OGLE-2002-BLG-055 has a single, but very reliable data point, deviating upward from a single source microlensing light curve by 0.6 mag. The simplest interpretation calls for a binary lens with a strong parallax effect and the mass ratio in the range of 0.01-0.001, putting the companion in the Jupiter mass range. Given only a single deviant point it is impossible to fit a unique model. We propose a modification of the OGLE observing strategy: instant verification of reality of future deviant points, followed by frequent time sampling, to make a unique model fit possible.
Preview · Article · Dec 2002 · Acta Astronomica -Warsaw and Cracow-
[Show abstract][Hide abstract] ABSTRACT: We present 18 binary lens candidates from OGLE-II database for seasons 1997-1999. The candidates have been selected by visual light curves inspection from the subsample of strong transient events; the same procedure gives 215 single lens candidates. Among the double lenses there are 12 cases interpreted as caustic crossing events. We compare the mass ratio and separation distributions obtained for binary lenses with the predictions based on stellar double systems observations. We take into account the selection bias, which causes over-representation of binary lenses of similar mass and separation close to the Einstein radius. There is no strong discrepancy between the expected and observed distributions of the mass ratio or the binary separations. We find two cases of binary lens candidates, SC20_1793 and SC20_3525, with extreme mass ratios, which may suggest presence of planets or brown dwarf companions. Unfortunately, neither case is very strong, as alternative solutions give fits to the data which are only unsubstantially worse. Binary lenses provide a modest contribution to overall optical depth to microlensing.