Spatially resolved microlensing timescale distributions across the Galactic bulge with the VVV survey
arxiv(2023)
摘要
We analyze 1602 microlensing events found in the VISTA Variables in the Via
Lactea (VVV) near-infrared (NIR) survey data. We obtain spatially-resolved,
efficiency-corrected timescale distributions across the Galactic bulge
(|ℓ|<10^∘, |b|<5^∘), using a Bayesian hierarchical model.
Spatially-resolved peaks and means of the timescale distributions, along with
their marginal distributions in strips of longitude and latitude, are in
agreement at a 1σ level with predictions based on the Besançon model
of the Galaxy. We find that the event timescales in the central bulge fields
(|ℓ| < 5^∘) are on average shorter than the non-central (|ℓ| >
5^∘) fields, with the average peak of the lognormal timescale distribution
at 23.6 ± 1.9 days for the central fields and 29.0 ± 3.0 days for the
non-central fields. Our ability to probe the structure of the Bulge with this
sample of NIR microlensing events is limited by the VVV survey's sparse cadence
and relatively small number of detected microlensing events compared to
dedicated optical surveys. Looking forward to future surveys, we investigate
the capability of the Roman telescope to detect spatially-resolved asymmetries
in the timescale distributions. We propose two pairs of Roman fields, centred
on (ℓ = ± 9,5^∘, b=-0.125^∘) and (ℓ = -5^∘, b=±
1.375^∘) as good targets to measure the asymmetry in longitude and
latitude, respectively.
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