KMT-2021-BLG-1077L: The fifth confirmed multiplanetary system detected
  by microlensing
  The high-magnification microlensing event KMT-2021-BLG-1077 exhibits a subtle
and complex anomaly pattern in the region around the peak. We analyze the
lensing light curve of the event with the aim of revealing the nature of the
anomaly. We test various models in combination with several interpretations. We
find that the anomaly cannot be explained by the usual three-body (2L1S and
1L2S) models. The 2L2S model improves the fit compared to the three-body
models, but it still leaves noticeable residuals. On the other hand, the 3L1S
interpretation yields a model explaining all the major anomalous features in
the lensing light curve. According to the 3L1S interpretation, the estimated
mass ratios of the lens companions to the primary are $\sim 1.56 \times
10^{-3}$ and $\sim 1.75 \times 10^{-3}$, which correspond to $\sim 1.6$ and
$\sim 1.8$ times the Jupiter/Sun mass ratio, respectively, and therefore the
lens is a multiplanetary system containing two giant planets. With the
constraints of the event time-scale and angular Einstein radius, it is found
that the host of the lens system is a low-mass star of mid-to-late M spectral
type with a mass of $M_{\rm h} = 0.14^{+0.19}_{-0.07}~M_\odot$, and it hosts
two gas giant planets with masses of $M_{\rm p_1}=0.22^{+0.31}_{-0.12}~M_{\rm
J}$ and $M_{\rm p_2}=0.25^{+0.35}_{-0.13}~M_{\rm J}$. The planets lie beyond
the snow line of the host with projected separations of $a_{\perp, {\rm
p}_1}=1.26^{+1.41}_{-1.08}~{\rm AU}$ and $a_{\perp, {\rm
p}_2}=0.93^{+1.05}_{-0.80}~{\rm AU}$. The planetary system resides in the
Galactic bulge at a distance of $D_{\rm L}=8.24^{+1.02}_{-1.16}~{\rm kpc}$. The
lens of the event is the fifth confirmed multiplanetary system detected by
microlensing following OGLE-2006-BLG-109L, OGLE-2012-BLG-0026L,
OGLE-2018-BLG-1011L, and OGLE-2019-BLG-0468L.
