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The Changing-look Phenomenon Accompanied by an Accretion Mode Transition in NGC 3786
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DOI：10.3847/1538-4357/ae6106.png)
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Abstract
En 中文
To reveal the physical origin of the changing-look (CL) phenomenon in NGC 3786, which transitioned from type 1.8/1.9 to type 1, we present an analysis of long-term spectral monitoring in the optical and near-infrared obtained with Gemini/GMOS-N and Gemini/GNIRS, respectively. Since the onset of the CL phenomenon, NGC 3786 has remained similar to 1-1.5 mag brighter in the mid-infrared than in the pre-CL stage, whereas the optical continuum has changed only moderately (similar to 0.2-0.3 mag). Spectroscopic analysis further reveals that while the fluxes of the broad Pa beta and Pa alpha lines were enhanced over a 2 yr follow-up period, the flux of the broad H alpha line remained unchanged. We propose that observed temporal variations in the continuum and line flux ratios disfavor a tidal disruption event origin. Instead, the observations can be primarily explained by a gradual change in line-of-sight extinction driven by variations in the torus covering factor, which is determined by the Eddington ratio and the accretion mode. An additional mechanism, arising from the physical conditions within the broad-line region, may partially account for the temporal evolution of the flux ratios. Our study highlights the importance of investigating the CL phenomenon in intermediate-type active galactic nuclei associated with outbursts detected only in the mid-infrared to explore the detailed structural evolution of nuclear activity.
Keywords:
ACTIVE GALACTIC NUCLEI
BROAD-LINE REGION
SUPERMASSIVE BLACK-HOLES
DUST COVERING FACTOR
DIGITAL SKY SURVEY
MIDINFRARED VARIABILITY
BALMER DECREMENT
SEYFERT-GALAXIES
STAR-FORMATION
1ES 1927+654
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5.4
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