A Candidate Binary Microlensing Event in the 2018 Gamma-Ray Flare of 3C 279

Yihong Yang; Jianeng Zhou; Haibin Ren; Wei Zhu; Haiyun Zhang; Dahai Yan; Hongping Deng; Hengxiao Guo; Zhen Yan; Liang Chen; Minfeng Gu

arXiv · 2610.40255

A Candidate Binary Microlensing Event in the 2018 Gamma-Ray Flare of 3C 279

Yihong Yang·Jianeng Zhou·Haibin Ren·Wei Zhu·Haiyun Zhang·Dahai Yan·Hongping Deng·Hengxiao Guo·Zhen Yan·Liang Chen·Minfeng Gu

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Abstract

The April 2018 gamma-ray flare of the flat-spectrum radio quasar 3C~279 exhibited sharp peaks within a broader outburst. Its rapid substructure was previously attributed to magnetic reconnection. Motivated by its distinctive temporal profile within our comparison sample of bright blazar flares and its resemblance to caustic-crossing features in optical microlensing events, we investigate a finite-source binary-microlensing interpretation. A jointly fitted model of binary-lens magnification, a smooth intrinsic flare, and Gaussian-process variability reproduces the principal double-peaked structure of the GeV light curve. The adopted local solution has a binary mass ratio of $q\simeq0.098$ and an Einstein timescale of $t_{\rm E}\simeq0.327$~d. The absolute lens mass and projected source radius depend on the lens distance and relative proper motion. The fitted geometry can correspond to a Galactic planetary-mass binary or an intervening stellar or substellar system, with different physical source sizes in each case. We present binary microlensing as a testable interpretation of this event, with the finite-source structure offering a potential probe of the compact GeV-emitting region.

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Yihong Yang, Jianeng Zhou, Haibin Ren, Wei Zhu, Haiyun Zhang, Dahai Yan, Hongping Deng, Hengxiao Guo, Zhen Yan, Liang Chen, Minfeng Gu. 2026-10-29. A Candidate Binary Microlensing Event in the 2018 Gamma-Ray Flare of 3C 279. https://arxiv.org/abs/2610.40255

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