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

By analyzing the information from NASA’s Swift spacecraft and from the Neutron Star Inside Composition Explorer (NICER) onboard the Worldwide House Station, astronomers have investigated an energetic optical transient often known as AT2021fxu. Outcomes of the examine, revealed December 14 on the arXiv preprint server, ship essential insights into the character of this transient, revealing that it’s a changing-look energetic 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 usually divide AGNs into two teams primarily based on emission line options. Kind 1 AGNs present broad and slim emission strains, whereas solely slim emission strains are current in Kind 2 AGNs. Nonetheless, observations revealed that some AGNs transition between completely different spectral varieties—they’re often 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 steered that it could be a CL AGN.

Lately, a staff of astronomers led by Yukta Ajay of the Indian Institute of Science Schooling and Analysis (IISER) in Tirupati, India, took a better take a look at AT2021fxu hoping to reveal its true nature. For this goal they inspected the out there 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 reveals the looks of broad emission strains (BELs). This means 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 Might 2000 and July 2021. This discovering signifies that the optical spectrum of ZTF21aalxxzn remained the identical through the talked about interval, and that the latest 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 consequence means that the CL transition is because of a variable accretion fee. Due to this fact, the authors of the paper concluded that AT2021fxu skilled an accretion-drive CL transition, during which the rise within the ionization flux is ready to produce sturdy broad Balmer strains that drives the change in spectral classification.

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