New highly variable quasar discovered

Analyzing data from astronomical surveys, Japanese astronomers have detected an extremely variable new quasi-stellar object (QSO), or quasar. The newly found object, designated SDSS J125809.31 + 351943.0, lit up in the optical band for 4.0 mag in three decades, meaning it was one of the largest quasar clearing events recorded to date. The discovery is reported in a document published on November 3 on arXiv.org.

Quasars are active galactic nuclei of very high luminosity, which emit electromagnetic radiation observable in radio, infrared, visible, ultraviolet and X-ray wavelengths. They are among the brightest and most distant objects in the known universe and serve as fundamental tools for numerous studies of astrophysics and cosmology. For example, quasars have been used to investigate the large-scale structure of the universe and the era of reionization. They also improved our understanding of the dynamics of supermassive black holes and the intergalactic medium.

Some distant quasars show large emission lines (BEL) appearing or disappearing, which is known as a so-called “appearance change” optical phenomenon. Most of these changing appearance quasars (CLQs) exhibit large variations in optical brightness greater than 1.0 mag. In addition to CLQs, such large changes in brightness were also observed in hyper-variable quasars (HVQs) and variable-state quasars (CSQs). The classification of HVQs is based on the variation of optical brightness, while that of CSQ is based on the variation of BEL, optical continuous flux density and mid-infrared brightness.

Now, a team of astronomers led by Shumpei Nagoshi of Kyoto University in Japan is reporting the discovery of a new quasar that exhibits a large amplitude of variability and appears to be a CSQ. The discovery of SDSS J125809.31 + 351943.0 (or J1258 for short) was based on data from programs including Survey and All Sky Automated Survey for Super Novae (ASAS-SN), Sloan Digital Sky Survey (SDSS) and Wide-Field Infrared Survey Explorer (WISE).

“We discovered an extremely variable quasar, SDSS J125809.31 + 351943.0, brightened for 4.0 mag from 1983 to 2015. We identified this object as a new CSQ based on the significant changes in mid-infrared brightness and the intensity of the broad emission line, “wrote the astronomers in the paper.

Observational data cover the period between 1983 and 2015. It was found that J1258 showed a monotonous increase in brightness of up to 4 magnets in about 30 years. Astronomers noted that this is one of the largest amplitudes of monotonous variations with the longest time scale of any quasar variability reported to date.

Additionally, observations revealed significant changes in mid-infrared brightness and the intensity of J1258’s broad emission line. The results also show the weakness of radio emission, which indicates that the variability is not caused by the quasar jet. Furthermore, it was found that the mid-infrared flux varied following the optical band. This supports the hypothesis that the accretion disk itself changed, rather than the change in absorption, took place.

The astronomers then concluded that J1258 is a CSQ and also one of the most drastically variable objects detected so far.

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