| 1. |
- Grishin, Evgeni, et al.
(författare)
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Supernova explosions in active galactic nuclear discs
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 507:1, s. 156-174
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Tidskriftsartikel (refereegranskat)abstract
- Active galactic nuclei (AGNs) are prominent environments for stellar capture, growth, and formation. These environments may catalyse stellar mergers and explosive transients, such as thermonuclear and core-collapse supernovae (SNe). SN explosions in AGN discs generate strong shocks, leading to unique observable signatures. We develop an analytical model that follows the evolution of the shock propagating in the disc until it eventually breaks out. We derive the peak luminosity, bolometric light curve, and breakout time. The peak luminosities may exceed 1045 erg s−1 and last from hours to days. The brightest explosions occur in regions of reduced density: either off-plane, or in discs around low-mass central black holes (∼106 M⊙), or in starved subluminous AGNs. Explosions in the latter two sites are easier to observe due to a reduced AGN background luminosity. We perform suites of 1D Lagrangian radiative hydrodynamics snec code simulations to validate our results and obtain the luminosity in different bands, and 2D axisymmetric Eulerian hydrodynamics code hormone simulations to study the morphology of the ejecta and its deviation from spherical symmetry. The observed signature is expected to be a bright blue, UV or X-ray flare on top of the AGN luminosity from the initial shock breakout, while the subsequent red part of the light curve will largely be unobservable. We estimate the upper limit for the total event rate to be R≲100 yr−1 Gpc−3 for optimal conditions and discuss the large uncertainties in this estimate. Future high-cadence transient searches may reveal these events. Some existing tidal disruption event candidates may originate from AGN SNe.
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| 2. |
- Korol, Valeriya, et al.
(författare)
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Merger rates in primordial black hole clusters without initial binaries
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 496:1, s. 994-1000
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Tidskriftsartikel (refereegranskat)abstract
- Primordial black holes formed through the collapse of cosmological density fluctuations have been hypothesized as contributors to the dark matter content of the Universe. At the same time, their mergers could contribute to the recently observed population of gravitational-wave sources. We investigate the scenario in which primordial black holes form binaries at late times in the Universe. Specifically, we re-examine the mergers of primordial black holes in small clusters of ∼30 objects in the absence of initial binaries. Binaries form dynamically through Newtonian gravitational interactions. These binaries act as heat sources for the cluster, increasing the cluster's velocity dispersion, which inhibits direct mergers through gravitational-wave two-body captures. Meanwhile, three-body encounters of tight binaries are too rare to tighten binaries sufficiently to allow them to merge through gravitational-wave emission. We conclude that in the absence of initial binaries, merger rates of primordial black holes in the considered scenario are at least an order of magnitude lower than previously suggested, which makes gravitational-wave detections of such sources improbable.
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| 3. |
- Levan, Andrew J., et al.
(författare)
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A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:8, s. 976-985
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Tidskriftsartikel (refereegranskat)abstract
- The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.
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| 4. |
- McBrien, Owen R., et al.
(författare)
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SN2018kzr : A Rapidly Declining Transient from the Destruction of a White Dwarf
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 885:1
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Tidskriftsartikel (refereegranskat)abstract
- We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of M-r & xfffd;=& xfffd;?17.98, a peak bolometric luminosity of ?1.4 & xfffd;& x5e0;10(43) erg s(?1), and a rapid decline rate of 0.48 & xfffd;& xfffd;0.03 mag day(?1) in the r band. The bolometric luminosity evolves too quickly to be explained by pure Ni-56 heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of M-ej & xfffd;=& xfffd;0.10 & xfffd;& xfffd;0.05 M. Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering?the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf?neutron star merger with energy from disk wind shocks.
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