Variable-looking events have been observed in the galaxy NGC 5273

Variable-looking events have been observed in the galaxy NGC 5273

ASAS-SN V-band (green) and g-band (lime) lightcurves NGC 5273. Credit: Neustadt et al, 2022

Astronomers analyzed new and archived multi-wavelength observations of the active galaxy NGC 5273. As a result, they detected so-called “variable appearance” events in the active galactic core of this galaxy. The finding is reported in a paper published November 7 on

An AGN is a compact region in the center of a galaxy, much brighter than the light of the surrounding galaxy. It is very active due to the presence of a black hole or star formation activity in the galactic core.

Astronomers generally divide AGNs into two groups based on their emission line features. Type 1 AGNs show broad and narrow emission lines, while only narrow emission lines are present in Type 2 AGNs. However, the observations revealed that some AGNs transition between different spectral types; Therefore, they are called morphologically variable (CL) AGNs.

At a distance of about 53.8 million light yearsNGC 5273 is a Syefert galaxy that hosts a low-light active galactic nucleus. NGC 5273’s AGN is relatively dim compared to other AGNs. Previous observations of this galaxy revealed that its brightness began to increase steadily in late 2021, and reached its peak in 2022.

Now, a team of Astronomy scientists Jack M.M. Neustadt of The Ohio State University in Columbus, Ohio announces the discovery of a new variable behavior of AGN in NGC 5273. The discovery was the result of detailed analysis of a wide range of infrared, optical and ultraviolet light. , and X-ray data obtained by various spacecraft and ground telescopes.

The study by Neustadt’s team found that at least one appearance-changing event occurred in NGC 5273. A type 1.8/1.9 Seyfert AGN changes to Type 1 as broad optical and near-infrared emission lines appear in the spectra, making the active galactic nucleus of NGC 5273 is one of the few AGNs known to change its appearance in the infrared.

The data show that the variable event in NGC 5273 coincides with an AGN eruption that occurred in 2014, and with evidence of historical variability prior to 2000. These results indicate that other flares in this galaxy may have been, as well. Temporary appearance change events from base type 1.8/1.9 to type 1.

Overall, the study found that the AGN of NGC 5273 varies by factors of 2 to 10 in the infrared-to-X-ray flux, with short flares in 2002, 2014, and 2016, and a long continuous flare beginning in late 2021.

Summarizing the results, the authors conclude that the variable appearance events in NGC 5273 are likely due to changes in how the broadline region (BLR) is reprocessed for continuous emission as evidenced by Eddington ratio change, Palmer regression, and broadline near emergence. Infrared emission lines.

“Changes in winds due to changes in λEdd could thus lead to changes in the BLR, although it is unclear how this would specifically affect Balmer decreases or NIR outlines,” explain the paper’s authors.

more information:
JMM Neustadt et al, Once an Example, Twice a Hobby: Multiple Optical and Variable Near-infrared Events in NGC 5273, arXiv (2022). DOI: 10.48550/arxiv.2211.03801

Journal information:

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