Palomar Gattini-IR NIR detection of a reddened Galactic binary microlensing event PGIR 19btb / AT 2019odt / Gaia 19dqj

ATel #13186; K. De (Caltech), P. Mroz (Caltech), M. Hankins (Caltech), M. M. Kasliwal (Caltech), M. Ashley (UNSW), A. Babul (Columbia), R. M. Lau (ISAS/JAXA), A. Moore (ANU), E. O. Ofek (Weizmann), M. Sharma (Columbia), J. Sokoloski (Columbia), J. Soon (ANU), R. Soria (NAOC), T. Travouillon (ANU) on behalf of the Palomar Gattini-IR team
on 11 Oct 2019; 22:59 UT
Credential Certification: Kishalay De (kde@astro.caltech.edu)

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We report the detection of a reddened Galactic binary microlensing event PGIR 19btb during regular survey operations of Palomar Gattini-IR. Palomar Gattini-IR is a wide-field NIR survey scanning the entire northern sky down to a depth of 16 AB mag every two nights (Moore & Kasliwal 2019).

PGIR 19btb (AT 2019odt / Gaia 19dqj) was found as a candidate transient generated in the real-time data reduction pipeline of Palomar Gattini-IR (De et al. in prep.), coincident with a quiescent 2MASS source with a J mag of 12.3 (all reported magnitudes are in the Vega system). The source exhibited a steady rise to a magnitude of J = 10.5 over 60 days followed by a rapid drop of 0.5 mags, and is now returning to its quiescent flux level.

The light curve shape is characteristic of a microlensing event with a static binary lens. We fit the light curve of the source with a binary lens model and are able to get an excellent fit (chi^2/dof = 49.3/50). We found two possible solutions with either q = 0.54 +/- 0.16, s = 1.28 +/- 0.02 (model 1) or q = 0.97 +/- 0.03, s = 1.25 +/- 0.01 (model 2), where q is the mass ratio and s is the binary separation in Einstein radius units. Multi-color photometric follow-up is encouraged as the lensing event is still ongoing.

We thank Jan Skowron for providing software for computation of microlensing magnifications.

Link to the light curve and models