Microlensing optical depth and event rate toward the Large Magellanic Cloud based on 20 years of OGLE observations
arxiv(2024)
摘要
Measurements of the microlensing optical depth and event rate toward the
Large Magellanic Cloud (LMC) can be used to probe the distribution and mass
function of compact objects in the direction toward that galaxy - in the Milky
Way disk, Milky Way dark matter halo, and the LMC itself. The previous
measurements, based on small statistical samples of events, found that the
optical depth is an order of magnitude smaller than that expected from the
entire dark matter halo in the form of compact objects. However, these previous
studies were not sensitive to long-duration events with Einstein timescales
longer than 2.5-3 years, which are expected from massive (10-100 M_⊙)
and intermediate-mass (10^2-10^5 M_⊙) black holes. Such events would
have been missed by the previous studies and would not have been taken into
account in calculations of the optical depth. Here, we present the analysis of
nearly 20-year-long photometric monitoring of 78.7 million stars in the LMC by
the Optical Gravitational Lensing Experiment (OGLE) from 2001 through 2020. We
describe the observing setup, the construction of the 20-year OGLE dataset, the
methods used for searching for microlensing events in the light curve data, and
the calculation of the event detection efficiency. In total, we find 16
microlensing events (thirteen using an automated pipeline and three with manual
searches), all of which have timescales shorter than 1 yr. We use a sample of
thirteen events to measure the microlensing optical depth toward the LMC
τ=(0.121 ± 0.037)× 10^-7 and the event rate Γ=(0.74 ±
0.25)× 10^-7 yr^-1 star^-1. These numbers are
consistent with lensing by stars in the Milky Way disk and the LMC itself, and
demonstrate that massive and intermediate-mass black holes cannot comprise a
significant fraction of dark matter.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要