Observation of a Solar-like Magnetic Reconnection Event in an AGN Corona with XRISM

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Abstract
The X-ray source in active galactic nuclei (AGNs) is commonly referred to as the corona by analogy to stellar coronae. The similarities between the two suggest that the heating mechanism of AGN coronae is magnetic reconnection—as in cool stars—but this has not yet been directly observed. This work presents the first observational evidence for a magnetic reconnection flare in an AGN corona. We report on a flare in NGC 3783, which was observed with XRISM/Xtend and XMM-Newton/EPIC exhibiting distinct temporal evolution in soft (2.0 keV) X-rays. An ultrafast outflow (UFO) was detected during the event. The flare features the Neupert effect—a temporal signature of the hard light curve correlating with the time derivative of the soft light curve, which shows that the flare is powered by magnetic reconnection. The Neupert effect is widely observed in the Sun, with coronal mass ejections (CMEs) playing a role analogous to the UFO. We derive an upper limit of 30 R g on the height of the magnetic loop from which the flare originates. Using the UFO measured properties to characterize the magnetic field, we obtain B > 1.3 × 10 4 G for the field annihilated during the flare from total energy considerations, and B ≈ 500 G for the momentary magnetic field during reconnection from a dynamical consideration.
Funding Information
  • Israel Science Foundation (2617/25)

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