Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBinary Source Lensing and the Repeating OGLE EWS Events
112
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic 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.
rate research
Read More
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.
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.
We present both the technical overview and main science drivers of the fourth phase of the Optical Gravitational Lensing Experiment (hereafter OGLE-IV). OGLE-IV is currently one of the largest sky variability surveys worldwide, targeting the densest stellar regions of the sky. The survey covers over 3000 square degrees in the sky and monitors regularly over a billion sources. The main targets include the inner Galactic Bulge and the Magellanic System. Their photometry spans the range of $12<I<21$ mag and $13<I<21.7$ mag, respectively. Supplementary shallower Galaxy Variability Survey covers the extended Galactic bulge and 2/3 of the whole Galactic disk within the magnitude range of $10<I<19$ mag. All OGLE-IV surveys provide photometry with milli-magnitude accuracy at the bright end. The cadence of observations varies from 19-60 minutes in the inner Galactic bulge to 1-3 days in the remaining Galactic bulge fields, Magellanic System and the Galactic disk. OGLE-IV provides the astronomical community with a number of real time services. The Early Warning System (EWS) contains information on two thousand gravitational microlensing events being discovered in real time annually, the OGLE Transient Detection System (OTDS) delivers over 200 supernovae a year. We also provide the real time photometry of unpredictable variables such as optical counterparts to the X-ray sources and R CrB stars. Hundreds of thousands new variable stars have already been discovered and classified by the OGLE survey. The number of new detections will be at least doubled during the current OGLE-IV phase. The survey was designed and optimized primarily to conduct the second generation microlensing survey for exoplanets. It has already contributed significantly to the increase of the discovery rate of microlensing exoplanets and free-floating planets.
We present an analysis of the results of the OGLE-III microlensing campaign towards the Large Magellanic Cloud (LMC). We evaluate for all the possible lens populations along the line of sight the expected microlensing quantities, number of events and duration. In particular we consider lensing by massive compact halo objects (MACHOs) in the dark matter haloes of both the Milky Way (MW) and the LMC, and self lensing by stars in the LMC bar and disc, in the MW disc and in the stellar haloes of both the LMC and the MW. As a result we find that the self-lensing signal is able to explain the 2 OGLE-III microlensing candidates. In particular, we estimate the expected MW disc signal to be almost as large as that from LMC stars and able, by itself, to explain the observed rate. We evaluate a 95% CL emph{upper} limit for $f$, the halo mass fraction in form of MACHOs, in the range 10-20% for $(10^{-2}-0.5) mathrm{M}_odot$, and $f=24%$ for $1 mathrm{M}_odot$ (below 10% in this full range, and in particular below 5% for $(10^{-2}-0.1) mathrm{M}_odot$) for the Bright (All) samples of source stars. Furthermore, we find that these limits do not rise much even if we assume the observed events emph{are} MACHOs. For the All sample we also evaluate a rather significant constraint on $f$ for larger values of the MACHO mass, in particular $fsim 50%$ (95% CL) for $100 mathrm{M}_odot$, to date the stronger bound coming from microlensing analyses in this mass range. Finally, we discuss these results in the framework of the previous observational campaigns towards the LMC, that of the MACHO and the EROS collaborations, and we present a joint analysis of the OGLE-II and the OGLE-III campaigns.
We analyze the microlensing event OGLE-2019-BLG-0304, whose light curve exhibits two distinctive features: a deviation in the peak region and a second bump appearing $sim 61$~days after the main peak. Although a binary-lens model can explain the overall features, it leaves subtle but noticeable residuals in the peak region. We find that the residuals can be explained by the presence of either a planetary companion located close to the primary of the binary lens (3L1S model) or an additional close companion to the source (2L2S model). Although the 3L1S model is favored over the 2L2S model, with $Deltachi^2sim 8$, securely resolving the degeneracy between the two models is difficult with the currently available photometric data. According to the 3L1S interpretation, the lens is a planetary system, in which a planet with a mass $0.51^{+0.51}_{-0.23}~M_{rm J}$ is in an S-type orbit around a binary composed of stars with masses $0.27^{+0.27}_{-0.12}~M_odot$ and $0.10^{+0.10}_{-0.04}~M_odot$. According to the 2L2S interpretation, on the other hand, the source is composed of G- and K-type giant stars, and the lens is composed of a low-mass M dwarf and a brown dwarf with masses $0.12^{+0.12}_{-0.05}~M_odot$ and $0.045^{+0.045}_{-.019}~M_odot$, respectively. The event illustrates the need for through model testing in the interpretation of lensing events with complex features in light curves.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
