ApJL study flags AT2019ijn as possible new class of relativistic blue optical transient

Astronomers led by Hucheng Ding of Anhui Normal University report multi-wavelength observations of AT2019ijn, a peculiar fast blue optical transient that may represent a new class of relativistic optical events, according to a phys.org writeup of a paper in The Astrophysical Journal Letters. AT2019ijn was first identified on May 31, 2019, by the Zwicky Transient Facility as an optical transient in the nucleus of a dwarf galaxy at redshift about 0.27. The source rose rapidly in the optical to a peak luminosity of -21.05 mag in 5.26 days, then declined slowly over more than a month while keeping a persistently blue color. Those traits generally resemble luminous fast-evolving blue optical transients, except for the slow decline, which is more consistent with superluminous supernovae or tidal disruption events. Radio emission was luminous and long-lasting, peaking 641 days after optical discovery. Peak radio luminosity was more than an order of magnitude higher than that of any other known luminous FBOT or superluminous supernova in the phys.org account, and comparable to jetted tidal disruption events. The ApJL abstract states the peak radio luminosity reached about (2.0 +/- 0.1) x 10^31 erg s^-1 Hz^-1, at least two orders of magnitude brighter than known radio-bright FBOTs and supernovae at similar epochs. The team argues the radio light curve fits an off-axis relativistic jet that spreads into the line of sight at late times. They favor a jetted tidal disruption event involving an intermediate-mass black hole of order 132,000 solar masses, while not fully ruling out a jetted magnetar. The abstract quotes a black hole mass near 1.32 x 10^5 solar masses. The researchers conclude that AT2019ijn may open a path for statistical studies that combine optical and radio time-domain surveys. The paper is DOI 10.3847/2041-8213/ae732c, published 2026 July 6 in ApJL.