AT2019ijn: a radio-bright blue transient that may mark a new class of cosmic explosion

Chinese astronomers report the discovery of a peculiar optical transient that could belong to a previously unrecognized class of relativistic explosions. The event, AT2019ijn, occurred in the nucleus of a dwarf galaxy at redshift z = 0.27, and does not match any known fast-evolving blue optical transient (FBOT) so far catalogued. The results were published on July 6, 2026, in The Astrophysical Journal Letters.

An unusual FBOT

AT2019ijn was first detected on May 31, 2019, by the Zwicky Transient Facility. In the optical, it rose to a peak luminosity of −21.05 mag in just 5.26 days, then declined slowly over more than a month while remaining persistently blue. The rapid rise fits the FBOT template, but the slow decay is more reminiscent of superluminous supernovae or tidal disruption events (TDEs).

Follow-up work led by Hucheng Ding (Anhui Normal University) shows that the radio emission is where AT2019ijn truly stands out. The radio flux was luminous and long-lasting, peaking 641 days after the optical discovery — more than one order of magnitude brighter than any known luminous FBOT or superluminous supernova, and comparable only to jetted TDEs.

A jetted intermediate-mass black hole

The team explains the delayed radio peak as an off-axis relativistic jet whose emission cone gradually swept into our line of sight. The estimated jet kinetic energy of ~7 × 10⁵³ erg, combined with the luminous optical light, points to an active central engine.

Their preferred scenario: a jetted TDE involving an intermediate-mass black hole of roughly 132,000 solar masses, tearing apart a passing star. A jetted magnetar remains as an alternative interpretation. Either way, the authors argue AT2019ijn’s combined optical and radio properties do not fit any established transient class — and may open the door to a new one, best identified by combining optical and radio time-domain surveys going forward.

© 2026 Homer Dávila Gutiérrez, FRAS — SKYCR.ORG. All rights reserved. Publication: Hucheng Ding et al., AT2019ijn: A Fast-rising, Slow-decaying Blue Optical Transient with Exceptionally Bright Radio Emission, The Astrophysical Journal Letters (2026). DOI: 10.3847/2041-8213/ae732c