NOCTURNE. II. Extreme radio variability in the heart of early-stage active galactic nuclei
Abstract
We report the discovery of extreme 37 GHz radio variability in early-stage active galactic nuclei (AGN). Most of these sources belong to the class of narrow-line Seyfert 1 (NLS1) galaxies, which harbour fast-growing, low-mass supermassive black holes that accrete at high Eddington ratios. At 37 GHz, these extraordinary AGN exhibit amplitude variability of three to four orders of magnitude over timescales of a few days. Notably, despite several attempts, we have not detected relativistic jets in these sources, suggesting that this phenomenon may occur very close to the black hole and may represent a new form of AGN variability. One of these sources, which flared at 37 GHz, was followed up with the Karl G. Jansky Very Large Array and Swift XRT/UVOT. Based on these observations, we estimated an e-folding timescale of mere hours, leading to variability brightness temperatures and variability Doppler factors that are extremely difficult to explain by an incoherent emitter. This suggests a possible detection of coherent emission from an AGN, although more observations will be needed to distinguish between alternative scenarios.
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BibTeX
@misc{jarvela2026nocturne,
title = {{NOCTURNE. II. Extreme radio variability in the heart of early-stage active galactic nuclei}},
author = {Emilia Järvelä and Patrizia Romano and Anne Lähteenmäki and Marco Berton},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16384},
eprint = {2609.16384},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16384},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - NOCTURNE. II. Extreme radio variability in the heart of early-stage active galactic nuclei
AU - Emilia Järvelä
AU - Patrizia Romano
AU - Anne Lähteenmäki
AU - Marco Berton
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.16384
UR - https://arxiv.org/abs/2609.16384
AB - We report the discovery of extreme 37 GHz radio variability in early-stage active galactic nuclei (AGN). Most of these sources belong to the class of narrow-line Seyfert 1 (NLS1) galaxies, which harbour fast-growing, low-mass supermassive black holes that accrete at high Eddington ratios. At 37 GHz, these extraordinary AGN exhibit amplitude variability of three to four orders of magnitude over timescales of a few days. Notably, despite several attempts, we have not detected relativistic jets in these sources, suggesting that this phenomenon may occur very close to the black hole and may represent a new form of AGN variability. One of these sources, which flared at 37 GHz, was followed up with the Karl G. Jansky Very Large Array and Swift XRT/UVOT. Based on these observations, we estimated an e-folding timescale of mere hours, leading to variability brightness temperatures and variability Doppler factors that are extremely difficult to explain by an incoherent emitter. This suggests a possible detection of coherent emission from an AGN, although more observations will be needed to distinguish between alternative scenarios.
ER -