Astronomers have conducted an observational campaign to investigate the extreme variability of the active galactic nucleus (AGN) SDSS J2232-0806, nicknamed the Big Dipper. The results of these observations, which were described in an article published on February 18 on the arXiv pre-print server, shed new light on the nature of this variability.
AGNs are compact regions in the center of galaxies that have more light than surrounding galaxy light. They are very energetic, either because of a black hole or the activity of star formation in the nucleus of the galaxy.
Significant multi-frequency variability over many timescales is one of the distinguishing features of AGNs. Mechanisms behind this variability are still controversial. Among the proposed explanations are changes in dust extinction, changes in the emission of the accretion disk or the associated comptonization regions, star arrest disturbances, supernovae in the core regions, and even the microlens of gravity.
In order to eliminate these uncertainties, further studies of the properties of AGN variability are required. One such study was conducted by a team of astronomers led by Daniel Kynoch of Durham University in the United Kingdom using various groundscopes. Researchers conducted an SDSS J2232-0806 optical photometric and spectroscopic surveillance campaign to investigate their variability. The Big Dipper is an AGN with a redshift of 0.276 and was initially classified as a "slow blue, hypervariable object".
"Here we report on an analysis of the eleven optical spectra obtained so far and compile a multi-wavelength data set with infrared, ultraviolet and X-ray observations," astronomers wrote in the newspaper.
The observations made by Kynoch's team experienced a significant dimming event and an increase over a period of about four years. In addition, archival photometric data suggests similar events in the past.
The researchers found that SDSS J2232-0806 appeared to be in a relatively bright state in the late 1980s, but in the data from the year 2000 observations. In addition, light curves from Catalina Sky Survey (CSS ) indicated that another slump had occurred between 2005 and 2007.
The analysis of the collected data allowed the team to exclude the extrinsic cause of the observed variability of SDSS J2232- 0806. They concluded that the variability of the object is most likely due to an intrinsic change in the luminosity of the accretion substance. This could be due to an intrinsic variation of continuum emission from the nuclear region, which is primarily triggered by processes within the accretion disk.
Although the researchers were unable to determine the exact origin of the variability of SDSS J2232-0806, they were. I hope future observations can answer that question. "SDSS J2232-0806 is one of a growing number of objects that challenge our models of viscous accretion disks, and although we can not determine the cause of the intrinsic brightness change, X-ray and UV monitoring of future episodes should greatly improve our understanding of the processes in progress", The scientists concluded.
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Daniel Kynoch et al. The & # 39; Big Dipper & # 39 ;: The nature of the extreme variability of AGN SDSS J2232-0806 arXiv: 1902.06753 [astro-ph.GA]. arxiv.org/abs/1902.06753