A Case of the Lensed AGN ULAS J081621.49+213442.65 at z ∼ 7.45 Confused with an Asteroid
Year: 2025
Type: article
Abstract: S. E. I. Bosman et al. proposed that the United Kingdom Infrared Telescope Infrared Deep Sky Survey Large Area Survey (UKIDSS LAS) detections of the high-redshift active galactic nucleus ULAS J081621.49+213442.65 in the 2008 data were caused by the transit of a moving object, rather than by ULAS J081621.49+213442.65 itself. Here, we have applied the optimal image subtraction method to the UKIDSS LAS J-band images from 2008, in which ULAS J081621.49+213442.65 was first detected. The resulting difference image showed that the transient of S. E. I. Bosman et al. has a previously unreported nearest counterpart located ∼24″ away from ULAS J081621.49+213442.65. The proposed identification of the source with a moving object is thus ruled out. ULAS J081621.49+213442.65 is a gravitationally lensed system consisting of four lensed images with a maximum separation of ∼2″. Astrometric and photometric behaviors similar to those of the UKIDSS LAS data were independently observed in 2024 during significant brightening of the same lensed images of ULAS J081621.49+213442.65 by >1 mag.
Source: Research Notes of the AAS
Authors: Ekaterina Koptelova, Chorng-Yuan Hwang
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4414313147