Abstract
Abstract
Infrared echo has proven to be an effective means to discover transient accretion events of supermassive black holes (SMBHs), such as tidal disruption events (TDEs) and changing-look active galactic nuclei (AGNs), in dusty circumnuclear environments. To explore the dusty populations of SMBH transient events, we have constructed a large sample of mid-infrared outbursts in nearby galaxies (MIRONG) and performed multiwavelength observations. Here we present the results of multiepoch spectroscopic follow-up observations of a subsample of 54 objects spanning a timescale of 4 yr. Emission-line variability was detected in 22 of them with either emergence or enhancement of broad Balmer emission lines in comparison with pre-outburst spectra. Coronal lines, He ii
λ4686, and Bowen line N iii
λ4640 appeared in the spectra of nine, seven, and two sources, respectively. These results suggest that MIRONG is a mixed bag of different transient sources. We have tentatively classified them into different subclass according to their spectral evolution and light curves. Two sources have been in a steady high broad Hα flux up to the latest observation and might be turn-on AGNs. Broad lines faded out in the remaining sources, indicating a transient ionizing source ignited by TDE or sporadic gas accretion. Thirty-one sources do not show noticeable spectral change with respect to their pre-outburst spectra. They have a statistically redder MIR color and lower MIR luminosity of the outbursts, which are consistent with heavily obscured events.
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
4 articles.
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