# Ground-based Parallax Confirmed by Spitzer: Binary Microlensing Event MOA-2015-BLG-020

Wang, T and Zhu, W and Mao, S and Bond, IA and Gould, A and Udalski, A and Sumi, T and Bozza, V and Ranc, C and Cassan, A and Yee, JC and Han, C and Abe, F and Asakura, Y and Barry, R and Bennett, DP and Bhattacharya, A and Donachie, M and Evans, P and Fukui, A and Hirao, Y and Itow, Y and Kawasaki, K and Koshimoto, N and Li, MCA and Ling, CH and Masuda, K and Matsubara, Y and Miyazaki, S and Muraki, Y and Nagakane, M and Ohnishi, K and Rattenbury, N and Saito, T and Sharan, A and Shibai, H and Sullivan, DJ and Suzuki, D and Tristram, PJ and Yamada, T and Yonehara, A and Kozlowski, S and Mroz, P and Pawlak, M and Pietrukowicz, P and Poleski, R and Skowron, J and Soszynski, I and Szymanski, MK and Ulaczyk, K and Beichman, C and Bryden, G and Novati, SC and Carey, S and Fausnaugh, M and Gaudi, BS and Henderson, CB and Shvartzvald, Y and Wibking, B and Albrow, MD and Chung, S-J and Hwang, K-H and Jung, YK and Ryu, Y-H and Shin, I-G and Cha, S-M and Kim, D-J and Kim, H-W and Kim, S-L and Lee, C-U and Lee, Y and Park, B-G and Pogge, RW and Street, RA and Tsapras, Y and Hundertmark, M and Bachelet, E and Dominik, M and Horne, K and Jaimes, RF and Wambsganss, J and Bramich, DM and Schmidt, R and Snodgrass, C and Steele, IA and Menzies, J (2017) Ground-based Parallax Confirmed by Spitzer: Binary Microlensing Event MOA-2015-BLG-020. ASTROPHYSICAL JOURNAL, 845 (2). ISSN 0004-637X

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Ground-based_parallax_confirmed_by_spitzer_binary_microlensing_event_MOA-2015-BLG-020.pdf - Published Version

We present the analysis of the binary gravitational microlensing event MOA-2015-BLG-020. The event has a fairly long timescale (~63 days) and thus the light curve deviates significantly from the lensing model that is based on the rectilinear lens-source relative motion. This enables us to measure the microlensing parallax through the annual parallax effect. The microlensing parallax parameters constrained by the ground-based data are confirmed by the Spitzer observations through the satellite parallax method. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined. It is found that the binary lens is composed of two dwarf stars with masses ${M}_{1}=0.606\pm 0.028\,{M}_{\odot }$ and ${M}_{2}=0.125\,\pm 0.006\,{M}_{\odot }$ in the Galactic disk. Assuming that the source star is at the same distance as the bulge red clump stars, we find the lens is at a distance ${D}_{L}=2.44\pm 0.10\,\mathrm{kpc}$. We also provide a summary and short discussion of all of the published microlensing events in which the annual parallax effect is confirmed by other independent observations.