Astronomers Identify AT2019ijn as a Possible New Class of Relativistic Cosmic Explosion With Record Radio Afterglow

Overview

An optical transient first spotted in 2019 has resurfaced as a scientific puzzle. A team led by Hucheng Ding of Anhui Normal University in China reports that the transient, cataloged as AT2019ijn, brightened and faded like known classes of stellar explosions but then produced radio emission so exceptional, more than a year and a half later, that the researchers argue it may represent an entirely new category of relativistic cosmic event, according to Phys.org. The findings were published July 6, 2026 in The Astrophysical Journal Letters.

What We Know

• AT2019ijn was first identified on May 31, 2019, by the Zwicky Transient Facility (ZTF) as an optical transient in the nucleus of a dwarf galaxy, according to Phys.org. The host galaxy sits at a redshift of z = 0.2729, and the paper describes it as a dwarf galaxy with a stellar mass of roughly 2×10⁸ solar masses, according to the arXiv preprint.
• In the optical band, the transient rose rapidly to a peak luminosity of magnitude −21.05 in 5.26 days, then declined slowly over more than a month while staying persistently blue, according to The Astrophysical Journal Letters.
• The story took a different turn in the radio band. Radio emission from AT2019ijn did not peak until 641 days after the optical discovery, and when it did, its luminosity was, in the researchers’ words, “at least two orders of magnitude brighter than known radio-bright fast blue optical transients and supernova explosions at similar epochs but comparable to jetted tidal disruption events,” according to The Astrophysical Journal Letters.
• The radio behavior was tracked across multiple facilities. AT2019ijn was detected as a bright S-band radio source as part of target observations by the Karl G. Jansky Very Large Array, was picked up by the Rapid ASKAP Continuum Survey and the Very Large Array Sky Survey, and prompted the team to trigger follow-up observations with the upgraded Giant Metrewave Radio Telescope, according to the arXiv preprint. The radio flux rose from about 5.97 mJy to 8.61 mJy over 229 days before beginning a slow decline that has lasted at least 1,690 days, according to the same preprint. Keck Observatory’s Low Resolution Imaging Spectrograph was used to characterize the host galaxy, the preprint adds.
• The research team favors an explanation in which AT2019ijn is a jetted tidal disruption event — a case in which a black hole’s gravity tears apart a passing star and launches a relativistic jet — involving an intermediate-mass black hole of roughly 1.32×10⁵ solar masses (about 132,000 solar masses), viewed off-axis at an angle of about 39 degrees, according to The Astrophysical Journal Letters.
• An alternative explanation involving a jetted magnetar “cannot be fully ruled out,” the paper states, but the arXiv preprint’s full text notes that a magnetar-powered scenario would be difficult to reconcile with the radio outflow’s inferred isotropic-equivalent energy, which reaches roughly 10⁵⁴ erg, “unless the energy release is strongly collimated into a very small solid angle,” according to the arXiv preprint.
• Separately, the team calculated a beaming-corrected jet kinetic energy of about 5.9×10⁵² erg, which they say points to a compact central engine such as a magnetar or an accreting black hole, according to the arXiv preprint.
• The paper’s own conclusion states that “AT2019ijn represents a new class of relativistic optical transients that highlights the importance of radio surveys for discovering off-axis jetted events,” according to The Astrophysical Journal Letters.
• For context, the team compared AT2019ijn to a small set of previously known jetted tidal disruption events, listing Sw J1644+57, Sw J1112-82, Sw J2058+05 and AT2022cmc as events viewed on-axis, and Arp 299-B AT1 and AT2018hyz as events viewed off-axis, according to the arXiv preprint.

What We Don’t Know

• The paper does not settle definitively between the jetted tidal disruption event and jetted magnetar scenarios; the magnetar model is described as difficult to reconcile with the observed radio energy rather than fully excluded, according to the arXiv preprint.
• Neither the journal article nor the arXiv preprint states the object’s distance in light-years, only its redshift value, so no light-year figure is reported here.
• It is not yet clear how many other transients of this kind exist in existing survey archives, since AT2019ijn’s identification relied on a multi-year radio follow-up campaign rather than being flagged at the time of its 2019 optical discovery.

Analysis

The five-year gap between AT2019ijn’s 2019 optical discovery and its 2026 publication as a possible new transient class underscores a point the researchers make explicitly: that late-time radio monitoring, not just rapid optical alerts, may be necessary to catch off-axis relativistic jets that would otherwise go unrecognized, according to The Astrophysical Journal Letters. AT2019ijn’s optical behavior — a fast rise followed by a slow, persistently blue decline — placed it in the same broad category as luminous fast blue optical transients, a group the paper describes as a subset of fast blue optical transients with peak luminosities brighter than magnitude −20, according to the arXiv preprint. But it was the radio behavior, arriving nearly two years after the optical fireworks had faded, that set AT2019ijn apart from every other member of that group the team examined.

Sources

This article draws on reporting from Phys.org, the peer-reviewed paper published in The Astrophysical Journal Letters, and the accompanying arXiv preprint by Hucheng Ding, Xinwen Shu, Luming Sun, Liangduan Liu, Lei Yang, Yunwei Yu, Xueguang Zhang, Ying Gu, Fangkun Peng, Fabao Zhang, Zhumao Zhang and Ningyu Tang.