Dark lenses through the dust: parallax microlensing events in the VVV

TL;DR

This study utilizes near-infrared data from the VVV survey to identify and analyze microlensing events with parallax information in obscured regions of the Galactic bulge, revealing potential dark remnants like neutron stars.

Contribution

It introduces a method to detect and characterize dark remnant lenses in highly extincted Galactic regions using microlensing parallax data from the VVV survey.

Findings

Identified 21 microlensing parallax candidates from 1959 events.

Detected 4 candidates with >50% probability of being dark lenses.

Found strong candidates likely to be neutron stars or high-mass white dwarfs.

Abstract

We use near-infrared photometry and astrometry from the VISTA Variables in the Via Lactea (VVV) survey to analyse microlensing events containing annual microlensing parallax information. These events are located in highly extincted and low-latitude regions of the Galactic bulge typically off-limits to optical microlensing surveys. We fit a catalog of $1959$ events previously found in the VVV and extract $21$ microlensing parallax candidates. The fitting is done using nested sampling to automatically characterise the multi-modal and degenerate posterior distributions of the annual microlensing parallax signal. We compute the probability density in lens mass-distance using the source proper motion and a Galactic model of disc and bulge deflectors. By comparing the expected flux from a main sequence lens to the baseline magnitude and blending parameter, we identify 4 candidates which have probability $> 50$% that the lens is dark. The strongest candidate corresponds to a nearby ($\approx0.78$ kpc), medium-mass ($1.46^{+1.13}_{-0.71} \ M_{\odot}$) dark remnant as lens. In the next strongest, the lens is located at heliocentric distance $\approx5.3$ kpc. It is a dark remnant with a mass of $1.63^{+1.15}_{-0.70} \ M_{\odot}$. Both of those candidates are most likely neutron stars, though possibly high-mass white dwarfs. The last two events may also be caused by dark remnants, though we are unable to rule out other possibilities because of limitations in the data.