Kavli Affiliate: Erin Kara
| First 5 Authors: Joheen Chakraborty, Riccardo Arcodia, Erin Kara, Giovanni Miniutti, Margherita Giustini
| Summary:
Quasi-Periodic Eruptions (QPEs) are luminous X-ray outbursts recurring on
hour timescales, observed from the nuclei of a growing handful of nearby
low-mass galaxies. Their physical origin is still debated, and usually modeled
as (a) accretion disk instabilities or (b) interaction of a supermassive black
hole (SMBH) with a lower mass companion in an extreme mass-ratio inspiral
(EMRI). EMRI models can be tested with several predictions related to the
short- and long-term behavior of QPEs. In this study, we report on the ongoing
3.5-year NICER and XMM-Newton monitoring campaign of eRO-QPE1, which is known
to exhibit erratic QPEs that have been challenging for the simplest EMRI models
to explain. We report 1) complex, non-monotonic evolution in the long-term
trends of QPE energy output and inferred emitting area; 2) the disappearance of
the QPEs (within NICER detectability) in October 2023, then reappearance by
January 2024 at a luminosity $sim$100x fainter (and temperature $sim$3x
cooler) than initial discovery; 3) radio non-detections with MeerKAT and VLA
observations partly contemporaneous with our NICER campaign (though not during
outbursts); and 4) the presence of a possible $sim$6-day modulation of the QPE
timing residuals, which aligns with the expected nodal precession timescale of
the underlying accretion disk. Our results tentatively support EMRI-disk
collision models powering the QPEs, and we demonstrate that the timing
modulation of QPEs may be used to jointly constrain the SMBH spin and disk
density profile.
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