The First Simultaneous Microlensing Observations by Two Space Telescopes: Spitzer and Swift Reveal a Brown Dwarf in Event Ogle-2015-BLG-1319

Abstract

Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the "microlens parallax." We report the discovery of a 30-65M J brown dwarf orbiting a K dwarf in the microlensing event OGLE-2015-BLG-1319. The system is located at a distance of ∼5 kpc toward the Galactic Bulge. The event was observed by several ground-based groups as well as by Spitzer and Swift, allowing a measurement of the physical properties. However, the event is still subject to an eight-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either ∼0.25 au or ∼45 au. This is the first microlensing event observed by Swift, with the UVOT camera. We study the region of microlensing parameter space to which Swift is sensitive, finding that though Swift could not measure the microlens parallax with respect to ground-based observations for this event, it can be important for other events. Specifically, it is important for detecting nearby brown dwarfs and free-floating planets in high magnification events.

OGLE-2014-BLG-1112LB: A Microlensing Brown Dwarf Detected through the Channel of a Gravitational Binary-lens Event

“…Since 2014, a space-based microlensing campaign using the Spitzer telescope, which is in solar orbit with a projected separation toward the bulge of d 1 au proj , has been conducted (Calchi . By successfully measuring microlens parallaxes of various types of lensing events, e.g., , Street et al (2016), Yee et al (2015), Shvartzvald et al (2016), Zhu et al (2015), Bozza et al (2016), and Han et al (2016), the campaign demonstrated that space-based parallaxes can be routinely measured for general lensing events. In the 2016 season, a new microlensing survey was conducted using the Kepler satellite, which has projected separations spanning < < d 0.07 au 0.81 au proj , over the course of the 2016 season (Henderson et al 2016).…”

OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing

“…Presently, 19 brown dwarfs have been detected by the microlensing method. Although the sample of microlensing brown dwarfs is still a small, it includes various types of brown dwarf systems such as isolated brown dwarfs (Poindexter et al 2005;Gould et al 2009;Zhu et al 2016;Chung et al 2017), brown dwarf companions to dwarf stars (Bachelet et al 2012;Bozza et al 2012;Shin et al 2012a,b;Park et al 2013Park et al , 2015Street et al 2013;Jung et al 2015;Ranc et al 2015;Shvartzvald et al 2016a), a brown dwarf binary , and a brown dwarf hosting a planet Shvartzvald et al 2017).…”

Measuring the Microlensing Parallax from Various Space Observatories

“…As shown by M16, a satellite in LEO is able to constrain the microlensing parallax, despite the relative low amplitude of the microlensing lightcurve's distortion due to the small orbital radius. Shvartzvald et al (2016) obtained ToO observation from Swift in order to constrain the parallax of the binary event OGLE-2015-BLG-1319. They showed that Swift should have been able to constrain the parallax in principle.…”