Prediction on detection and characterization of Galactic disk microlensing events by LSST

Abstract

Upcoming LSST survey gives an unprecedented opportunity for studying populations of intrinsically faint objects using microlensing technique. Large field of view and aperture allow effective time-series observations of many stars in Galactic disk and bulge. Here, we combine Galactic models (for |b|<10 deg) and simulations of LSST observations to study how different observing strategies affect the number and properties of microlensing events detected by LSST. We predict that LSST will mostly observe long duration microlensing events due to the source stars with the averaged magnitude around 22 in r-band, rather than high-magnification events due to fainter source stars. In Galactic bulge fields, LSST should detect on the order of 400 microlensing events per square degree as compared to 15 in disk fields. Improving the cadence increases the number of detectable microlensing events, e.g., improving the cadence from 6 to 2 days approximately doubles the number of microlensing events throughout the Galaxy. According to the current LSST strategy, it will observe some fields 900 times during a 10-year survey with the average cadence of ~4-days (I) and other fields (mostly toward the Galactic disk) around 180 times during a 1-year survey only with the average 1-day cadence (II). We anticipate that the number of events corresponding to these strategies are 7900 and 34000, respectively. Toward similar lines of sight, LSST with the first observing strategy (I) will detect more and on average longer microlensing events than those observable with the second strategy. If LSST spends enough time observing near Galactic plane, then the large number of microlensing events will allow studying Galactic distribution of planets and finding isolated black holes among wealth of other science cases.

Submitted to The Astrophysical Journal, 15 pages, 6 tables, 9 figures, comments are welcomed

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