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The Richness-to-Mass Relation of CAMIRA Galaxy Clusters from Weak-lensing Magnification in the Subaru Hyper Suprime-Cam Survey

We present a statistical weak-lensing magnification analysis on an optically selected sample of 3029 \texttt{CAMIRA} galaxy clusters with richness $N>15$ at redshift $0.2\leq z <1.1$ in the Subaru Hyper Suprime-Cam (HSC) survey. We use two distinct populations of color-selected, flux-limited background galaxies, namely the low-$z$ and high-$z$ samples at mean redshifts of $\approx1.1$ and $\approx1.4$, respectively, from which to measure the weak-lensing magnification signal by accounting for cluster contamination as well as masking effects. Our magnification bias measurements are found to be uncontaminated according to validation tests against the "null-test" samples for which the net magnification bias is expected to vanish. The magnification bias for the full \texttt{CAMIRA} sample is detected at a significance level of $9.51σ$, which is dominated by the high-$z$ background. We forward-model the observed magnification data to constrain the normalization of the richness-to-mass ($N$--$M$) relation for the \texttt{CAMIRA} sample with informative priors on other parameters. The resulting scaling relation is $N\propto {M_{500}}^{0.92\pm0.13} (1 + z)^{-0.48\pm0.69}$, with a characteristic richness of $N=\left(17.72\pm2.60\right)$ and intrinsic log-normal scatter of $0.15\pm0.07$ at $M_{500} = 10^{14}h^{-1}M_{\odot}$. With the derived $N$--$M$ relation, we provide magnification-calibrated mass estimates of individual \texttt{CAMIRA} clusters, with the typical uncertainty of $\approx39\%$ and $\approx32\%$ at richness$\approx20$ and $\approx40$, respectively. We further compare our magnification-inferred $N$--$M$ relation with those from the shear-based results in the literature, finding good agreement.