NICER observation list: Target ID 852801

Recently, a subset of early-stage active galactic nuclei with extreme high radio frequency (37 GHz) variability was discovered. These sources, all narrow-line Seyfert 1 galaxies, exhibit variability with an amplitude of three to four orders of magnitude on a timescale of days. The origin of this behaviour is currently unknown, but there is preliminary evidence that the radio flares are connected to X-ray flares. We will use NICER ToO X-ray monitoring, triggered by a 37 GHz radio flare, to constrain the models proposed to explain the variability and to probe the apparent but unexpected high-frequency radio vs. X-ray association. The unique X-ray signatures of the models can be used to distinguish between them, possibly leading to a breakthrough in understanding these extraordinary sources.