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On 23 July 2016 after 05:00\,UTC, the first 48-antenna stage of the SiberianRadioheliograph detected two flares of M7.6 and M5.5 GOES importance thatoccurred within half an hour in the same active region. Their multi-instrumentanalysis reveals the following. The microwave spectra were flattened at lowfrequencies and the spectrum of the stronger burst had a lower turnoverfrequency. Each flare was eruptive, emitted hard X-rays and gamma-raysexceeding 800\,keV, and had a rare three-ribbon configuration. An extended hardX-ray source associated with a longest middle ribbon was observed in the secondflare. The unusual properties of the microwave spectra are accounted for by adistributed multi-loop system in an asymmetric magnetic configuration that ourmodeling confirms. Microwave images did not to resolve compact configurationsin these flares that may also be revealed incompletely in hard X-ray imagesbecause of their limited dynamic range. Being apparently simple and compact,non-thermal sources corresponded to the structures observed in the extremeultraviolet. In the scenario proposed for two successive three-ribbon eruptiveflares in a configuration with a coronal-null region, the first eruption causesa flare and facilitates the second eruption that also results in a flare.

Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra