AT2021fxu is a changing-look active galactic nucleus, observations find

By analyzing the info from NASA’s Swift spacecraft and from the Neutron Star Inside Composition Explorer (NICER) onboard the Worldwide Area Station, astronomers have investigated an lively optical transient generally known as AT2021fxu. Outcomes of the research, printed December 14 on the arXiv preprint server, ship necessary insights into the character of this transient, revealing that it’s a changing-look lively galactic nucleus.

An active galactic nucleus (AGN) is a compact area on the middle of a galaxy, extra luminous than the encircling galaxy mild. They’re very energetic due both to the presence of a black hole or star formation exercise on the core of the galaxy.

Astronomers typically divide AGNs into two teams primarily based on emission line options. Kind 1 AGNs present broad and slender emission strains, whereas solely slender emission strains are current in Kind 2 AGNs. Nevertheless, observations revealed that some AGNs transition between completely different spectral sorts—they’re generally known as changing-look (CL) AGNs.

At a redshift of roughly 0.11, AT2021fxu (different designations: ZTF21aalxxzn and Gaia22dgm) is an optical transient recognized throughout an outburst by the Zwicky Transient Facility (ZTF) on February 13, 2021. Some research have recommended that it could be a CL AGN.

Lately, a crew of astronomers led by Yukta Ajay of the Indian Institute of Science Training and Analysis (IISER) in Tirupati, India, took a more in-depth take a look at AT2021fxu hoping to reveal its true nature. For this objective they inspected the obtainable multiwavelength knowledge from Swift and NICER.

“Right here we current evaluation of AT2021fxu’s multiwavelength knowledge taken over a temporal baseline of over 20 years,” the researchers wrote within the paper.

By analyzing the optical, ultraviolet and X-ray knowledge, the astronomers discovered that the optical spectrum of ZTF21aalxxzn clearly exhibits the looks of broad emission strains (BELs). This implies that the supply underwent a spectral transition from a Kind 2 to a Kind 1 AGN, throughout which the brightness within the particular person photometric bands elevated as much as roughly 0.6 magazine within the optical bands and as much as about 1.1 magazine within the ultraviolet bands.

Moreover, the optical g- and r- magnitudes of ZTF21aalxxzn have remained fixed between Could 2000 and July 2021. This discovering signifies that the optical spectrum of ZTF21aalxxzn remained the identical throughout the talked about interval, and that the current optical outburst marks the onset of the CL transition on this AGN.

The X-ray spectral evaluation of ZTF21aalxxzn discovered that there’s minimal variation within the column density over the noticed time. This outcome means that the CL transition is because of a variable accretion charge. Subsequently, the authors of the paper concluded that AT2021fxu skilled an accretion-drive CL transition, by which the rise within the ionization flux is ready to produce robust broad Balmer strains that drives the change in spectral classification.

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