Statistical Searches for Microlensing Events in Large, Non-Uniformly Sampled Time-Domain Surveys: A Test Using Palomar Transient Factory Data

Abstract

Many photometric time-domain surveys are driven by specific goals, such as searches for supernovae or transiting exoplanets, which set the cadence with which fields are re-imaged. In the case of the Palomar Transient Factory (PTF), several sub-surveys are conducted in parallel, leading to non-uniform sampling over its $\sim$$20,000{\mathrm{deg}}^2$ footprint. While the median $7.26{\mathrm{deg}}^2$ PTF field has been imaged $\sim$40 times in \textit{R}-band, $\sim$$2300{\mathrm{deg}}^2$ have been observed $>$100 times. We use PTF data to study the trade-off between searching for microlensing events in a survey whose footprint is much larger than that of typical microlensing searches, but with far-from-optimal time sampling. To examine the probability that microlensing events can be recovered in these data, we test statistics used on uniformly sampled data to identify variables and transients. We find that the von Neumann ratio performs best for identifying simulated microlensing events in our data. We develop a selection method using this statistic and apply it to data from fields with $>$10 $R$-band observations, $1.1\times 10^9$ light curves, uncovering three candidate microlensing events. We lack simultaneous, multi-color photometry to confirm these as microlensing events. However, their number is consistent with predictions for the event rate in the PTF footprint over the survey's three years of operations, as estimated from near-field microlensing models. This work can help constrain all-sky event rate predictions and tests microlensing signal recovery in large data sets, which will be useful to future time-domain surveys, such as that planned with the Large Synoptic Survey Telescope.

13 pages, 14 figures; accepted for publication in ApJ. fixed author list

References in corpus (12)

• Astropy: A Community Python Package for Astronomy
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• Stellar SEDs from 0.3-2.5 Microns: Tracing the Stellar Locus and Searching for Color Outliers in SDSS and 2MASS
• Characterizing the Mid-IR Extragalactic Sky with WISE and SDSS
• A White Light Megaflare on the dM4.5e Star YZ CMi
• Using Machine Learning for Discovery in Synoptic Survey Imaging
• The Palomar Transient Factory photometric catalog 1.0
• Discovery of a Very Bright, Nearby Gravitational Microlensing Event
• Mesolensing Explorations of Nearby Masses: From Planets to Black Holes
• Near-Field Microlensing from Wide-Field Surveys
• Determination of stellar shape in microlensing event MOA 2002-BLG-33
• Observation of the first gravitational microlensing event in a sparse stellar field : the Tago event

Cited by in corpus (11)

• A Population of Short-Period Variable Quasars from PTF as Supermassive Black Hole Binary Candidates
• Optical variability of AGN in the PTF/iPTF survey
• Long-Term Decline of the Mid-Infrared Emission of Normal Galaxies: Dust Echo of Tidal Disruption Flare?
• On the radial distribution of giant exoplanets at Solar System scales
• A Machine Learning Classifier for Microlensing in Wide-Field Surveys
• Gaia transients in galactic nuclei
• The fast transient sky with Gaia
• OGLE-BLG182.1.162852: An Eclipsing Binary with a Circumstellar Disk
• A microlensing search of 700 million VVV light curves
• 60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One
• Gravitational Microlensing Event Statistics for the Zwicky Transient Facility