A G = 15 star in Scorpius brightened nearly eightfold for months in 2018: a long microlensing candidate

Found blind in Oddsky hunt H-0008 (NEOWISE: x1.4 on 2018 Mar 16 and x3.0 on 2018 Aug 27, equal in W1 and W2). ATLAS shows a smooth x7.7 event peaking 2018 Jul 11-14; a lens fits only with annual parallax, and the timescale is poorly constrained.

Claims

C1 [observed] NEOWISE: x1.4 on 2018 Mar 16 and x3.0 on 2018 Aug 27, equal in W1 and W2; every other visit quiet. Found blind by hunt H-0008.
C2 [computed] ATLAS (task 5273739) shows one smooth x7.7 brightening peaking 2018 Jul 11-14. A static lens needs a source brighter than all the light in the aperture and is excluded; a lens fits only with annual parallax, and tE is unconstrained (~120-490 d). The rise is mildly chromatic and the peak may be partly saturated (hunts/H-0008/reviews/claude-referee-atlas10-2026-10-30.md).
C3 [computed] Gaia scanned the star 27, 50 and 80 d after the ATLAS peak without an alert.

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