Kavli Affiliate: Dheeraj Pasham
| First 5 Authors: Dheeraj Pasham, Shubham Kejriwal, Eric Coughlin, Vojtěch Witzany, Alvin J. K. Chua
| Summary:
Quasi-periodic eruptions (QPEs) are recurring bursts of soft X-rays from the
nuclei of galaxies. Their physical origin is currently a subject of debate,
with models typically invoking an orbiter around a massive black hole or disk
instabilities. Here we present and analyze the temporal and spectral evolution
of the QPE source eRO-QPE2 over 3.5 years. We find that eRO-QPE2 1) is
remarkably stable over the entire 3.5-year temporal baseline in its eruption
peak luminosity, eruption temperature, quiescent temperature, and quiescent
luminosity, 2) has a stable mean eruption recurrence time of 2.35 hours, with
marginal ($sim$2$sigma$) evidence for a $0.1$ hour reduction over the 3.5 yr
period, and 3) has a long-short variation in its recurrence time in August
2020, but this pattern is absent from all subsequent observations. The
stability of its peak eruption luminosity and that of the quiescent state are
notably dissimilar from three previously tracked QPEs (GSN069, eRO-QPE1,
eRO-QPE3), which show declines in eruption and quiescent flux over comparable
temporal baselines. This stability is even more pronounced in eRO-QPE2 due to
its 2.4 hour average recurrence time compared to GSN-069’s 9 hour, eRO-QPE1’s
16 hour, and eRO-QPE3’s 20 hour recurrence times, i.e., this system has
undergone 4-8 times more cycles than these other systems over the 3.5 years of
observations. We discuss the implications of these observations within the
context of some proposed extreme mass ratio inspiral (EMRI) models.
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