18 research outputs found
Science with a small two-band UV-photometry mission III: Active Galactic Nuclei and nuclear transients
In this review (the third in the series focused on a small two-band
UV-photometry mission), we assess possibilities for a small UV two-band
photometry mission in studying accreting supermassive black holes (SMBHs; mass
range -). We focus on the following
observational concepts: (i) dedicated monitoring of selected type-I Active
Galactic Nuclei (AGN) in order to measure the time delay between the far-UV,
the near-UV, and other wavebands (X-ray and optical), (ii) nuclear transients
including (partial) tidal disruption events and repetitive nuclear transients,
and (iii) the study of peculiar sources, such as changing-look AGN, hollows and
gaps in accretion disks, low-luminosity AGN, and candidates for
Intermediate-Mass Black Holes (IMBHs; mass range -)
in galactic nuclei. For tidal disruption events (TDEs), high-cadence UV
monitoring is crucial for distinguishing among different scenarios for the
origin of the UV emission. The small two-band UV space telescope will also
provide the information about the near- and far-UV continuum variability for
rare transients, such as repetitive partial TDEs and jetted TDEs. We also
discuss the possibilities to study and analyze sources with non-standard
accretion flows, such as AGN with gappy disks, low-luminosity active galactic
nuclei with intermittent accretion, and SMBH binaries potentially involving
intermediate-mass black holes.Comment: Submitted to Space Science Review
Alive but Barely Kicking: News from 3+ yr of Swift and XMM-Newton X-Ray Monitoring of Quasiperiodic Eruptions from eRO-QPE1
Quasiperiodic eruptions (QPEs) represent a novel class of extragalactic X-ray transients that are known to repeat at roughly regular intervals of a few hours to days. Their underlying physical mechanism is a topic of heated debate, with most models proposing that they originate either from instabilities within the inner accretion flow or from orbiting objects. At present, our knowledge of how QPEs evolve over an extended timescale of multiple years is limited, except for the unique QPE source GSN 069. In this study, we present results from strategically designed Swift observing programs spanning the past 3 yr, aimed at tracking eruptions from eRO-QPE1. Our main results are as follows: (1) the recurrence time of eruptions can vary from flare to flare and is in the range of 0.6–1.2 days; (2) there is no detectable secular trend in evolution of the recurrence times; (3) consistent with prior studies, their eruption profiles can have complex shapes; and (4) the peak flux of the eruptions has been declining over the past 3 yr, with the eruptions barely detected in the most recent Swift data set taken in 2023 June. This trend of weakening eruptions has been reported recently in GSN 069. However, because the background luminosity of eRO-QPE1 is below our detection limit, we cannot verify whether the weakening is correlated with the background luminosity (as is claimed to be the case for GSN 069). We discuss these findings within the context of various proposed QPE models