Science with a Small Two-Band UV-Photometry Mission I: Mission Description and Follow-up Observations of Stellar Transients

Werner, N.; Řípa, J.; Thöne, C.; Münz, F.; Kurfürst, P.; Jelínek, M.; Hroch, F.; Benáček, J.; Topinka, M.; Lukes-Gerakopoulos, G.; Zajaček, M.; Labaj, M.; Prišegen, M.; Krtička, J.; Merc, J.; Pál, A.; Pejcha, O.; Dániel, V.; Jon, J.; Šošovička, R.; Gromeš, J.; Václavík, J.; Steiger, L.; Segiňák, J.; Behar, E.; Tarem, S.; Salh, J.; Reich, O.; Ben-Ami, S.; Barschke, M. F.; Berge, D.; Tohuvavohu, A.; Sivanandam, S.; Bulla, M.; Popov, S.; Chang, Hsiang-Kuang

doi:10.1007/s11214-024-01048-3

“…Most notably, the Ultraviolet Transient Astronomy Satellite (ULTRASAT; Sagiv et al 2014) will provide high etendue monitoring of the UV sky following its planned launch in 2025. The Czech UV satellite mission QUVIK (Werner et al 2024) will provide similar capabilities, though with a shorter wavelength sensitivity and somewhat smaller field of view. The proposed space mission Ultraviolet Explorer (UVEX; Kulkarni et al 2021) will perform a cadenced all-sky survey with greater sensitivity and covering a wider UV wavelength range, with both a near-UV and far-UV band, as well as UV spectroscopy capabilities.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet Quasiperiodic Eruptions from Star–Disk Collisions in Galactic Nuclei

Linial,

Metzger

2024

ApJL

7

0

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“Quasiperiodic eruptions” (QPE) are recurrent nuclear transients with periods of several hours to almost a day, which thus far have been detected exclusively in the X-ray band. We have shown that many of the key properties of QPE flares (period, luminosity, duration, emission temperature, alternating long-short recurrence time behavior, and source rates) are naturally reproduced by a scenario involving twice-per-orbit collisions between a solar-type star on a mildly eccentric orbit, likely brought into the nucleus as an extreme mass-ratio inspiral (EMRI), and the gaseous accretion disk of a supermassive black hole (SMBH). The flare is generated by the hot shocked debris expanding outwards from either side of the disk midplane, akin to dual miniature supernovae. Here, we consider the conditions necessary for disk–star collisions to generate lower-temperature flares that peak in the ultraviolet (UV) instead of the X-ray band. We identify a region of parameter space at low SMBH mass M • ∼ 105.5 M ⊙ and QPE periods P ≳ 10 hr for which the predicted flares are sufficiently luminous L UV ∼ 1041 erg s−1 to outshine the quiescent disk emission at these wavelengths. The prospects to discover such “UV QPEs” with future satellite missions such as ULTRASAT and Ultraviolet Explorer depend on the prevalence of very low-mass SMBHs and the occurrence rate of stellar EMRIs onto them. For gaseous disks produced by the tidal disruption of stars, we predict that X-ray QPEs will eventually shut off, only to later reappear as UV QPEs as the accretion rate continues to drop.

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Science with a Small Two-Band UV-Photometry Mission II: Observations of Stars and Stellar Systems

Krtička,

Benáček,

Budaj

et al. 2024

Space Sci Rev

2

0

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We outline the impact of a small two-band UV-photometry satellite mission on the field of stellar physics, magnetospheres of stars, binaries, stellar clusters, interstellar matter, and exoplanets. On specific examples of different types of stars and stellar systems, we discuss particular requirements for such a satellite mission in terms of specific mission parameters such as bandpass, precision, cadence, and mission duration. We show that such a mission may provide crucial data not only for hot stars that emit most of their light in UV, but also for cool stars, where UV traces their activity. This is important, for instance, for exoplanetary studies, because the level of stellar activity influences habitability. While the main asset of the two-band UV mission rests in time-domain astronomy, an example of open clusters proves that such a mission would be important also for the study of stellar populations. Properties of the interstellar dust are best explored when combining optical and IR information with observations in UV.It is well known that dust absorbs UV radiation efficiently. Consequently, we outline how such a UV mission can be used to detect eclipses of sufficiently hot stars by various dusty objects and study disks, rings, clouds, disintegrating exoplanets or exoasteroids. Furthermore, UV radiation can be used to study the cooling of neutron stars providing information about the extreme states of matter in the interiors of neutron stars and used for mapping heated spots on their surfaces.

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Science with a Small Two-Band UV-Photometry Mission III: Active Galactic Nuclei and Nuclear Transients

Zajaček,

Czerny,

Jaiswal

et al. 2024

Space Sci Rev

1

0

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In this review, the third one 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 $\sim 10^{6}$ ∼ 10 6 –$10^{10}\,M_{\odot }$ 10 10 M ⊙ ). 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 $\sim 10^{2}$ ∼ 10 2 –$10^{5}\,M_{\odot }$ 10 5 M ⊙ ) in galactic nuclei. The importance of a small UV mission for the observing program (i) is to provide intense, high-cadence monitoring of selected sources, which will be beneficial for, e.g. reverberation-mapping of accretion disks and subsequently confronting accretion-disk models with observations. For program (ii), a relatively small UV space telescope is versatile enough to start monitoring a transient event within ≲ 20 minutes after receiving the trigger; such a moderately fast repointing capability will be highly beneficial. Peculiar sources within the program (iii) will be of interest to a wider community and will create an environment for competitive observing proposals. 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 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.

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Science with a Small Two-Band UV-Photometry Mission I: Mission Description and Follow-up Observations of Stellar Transients

Cited by 6 publications

References 210 publications

Ultraviolet Quasiperiodic Eruptions from Star–Disk Collisions in Galactic Nuclei

Ultraviolet Quasiperiodic Eruptions from Star–Disk Collisions in Galactic Nuclei

Science with a Small Two-Band UV-Photometry Mission II: Observations of Stars and Stellar Systems

Science with a Small Two-Band UV-Photometry Mission III: Active Galactic Nuclei and Nuclear Transients

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