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1.
2.
Lens parameters for Gaia18cbf – a long gravitational microlensing event in the Galactic plane
K. Kruszyńska, Ł. Wyrzykowski, K. A. Rybicki, M. Maskoliūnas, E. Bachelet, N. Rattenbury, P. Mróz, P. Zieliński, K. Howil, Z. Kaczmarek, S. T. Hodgkin, N. Ihanec, I. Gezer, M. Gromadzki, P. Mikołajczyk, A. Stankevičiūtė, V. Čepas, E. Pakštienė, K. Šiškauskaitė, J. Zdanavičius, V. Bozza, M. Dominik, R. Figuera Jaimes, A. Fukui, M. Hundertmark, N. Narita, R. Street, Y. Tsapras, Mateusz Bronikowski, M. Jabłońska, A. Jabłonowska, O. Ziółkowska, 2022, original scientific article

Abstract: Context. The timescale of a microlensing event scales as a square root of a lens mass. Therefore, long-lasting events are important candidates for massive lenses, including black holes. Aims. Here, we present the analysis of the Gaia18cbf microlensing event reported by the Gaia Science Alerts system. It exhibited a long timescale and features that are common for the annual microlensing parallax effect. We deduce the parameters of the lens based on the derived best fitting model. Methods. We used photometric data collected by the Gaia satellite as well as the follow-up data gathered by the ground-based observatories. We investigated the range of microlensing models and used them to derive the most probable mass and distance to the lens using a Galactic model as a prior. Using a known mass-brightness relation, we determined how likely it is that the lens is a main-sequence (MS) star. Results. This event is one of the longest ever detected, with the Einstein timescale of tE = 491.41−84.94+128.31 days for the best solution and tE = 453.74−105.74+178.69 days for the second best. Assuming Galaxy priors, this translates to the most probable lens masses of ML = 2.65−1.48+5.09 M⊙ and ML = 1.71−1.06+3.78 M⊙, respectively. The limits on the blended light suggest that this event was most likely not caused by a MS star, but rather by a dark remnant of stellar evolution.
Keywords: gravitational lensing: micro, Galaxy: stellar content, stars: black holes, stars: neutron, Astrophysics - Solar and Stellar Astrophysics
Published in RUNG: 13.11.2023; Views: 839; Downloads: 4
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3.
Studying TDEs in the era of LSST
Katja Bricman, Andreja Gomboc, 2019, published scientific conference contribution abstract

Keywords: The observing strategy with continuous scanning and large sky coverage of the upcoming ground-based Large Synoptic Survey Telescope (LSST) will make it a perfect tool in search of rare transients, such as Tidal Disruption Events (TDEs). Bright optical flares resulting from tidal disruption of stars by their host supermassive black hole (SMBH) can provide us with important information about the mass of the SMBH involved in the disruption and thus enable the study of quiescent SMBHs, which represent a large majority of SMBHs found in centres of galaxies. These types of transients are extremely rare, with only about few tens of candidates discovered so far. It is expected that the LSST will provide a large sample of new TDE light curves. Here we present simulations of TDE observations using an end-to-end LSST simulation framework. Based on the analysis of simulated light curves we estimate the number of TDEs with good quality light curves the LSST is expected to discover in 10 years of observations. In addition, we investigate whether TDEs observed by the LSST could be used to probe the SMBH mass distribution in the universe. The participation at this conference is supported by the Action CA16104 Gravitational waves, black holes and fundamental physics (GWverse), supported by COST (European Cooperation in Science and Technology).
Published in RUNG: 04.01.2021; Views: 2760; Downloads: 0

4.
On the GeV Emission of the Type I BdHN GRB 130427A
Remo Ruffini, Rahim Moradi, Jorge Armando Rueda, Carlo Luciano Bianco, Christian Cherubini, Simonetta Filippi, Yen-Chen Chen, Mile Karlica, Narek Sahakyan, Yu Wang, She Sheng Xue, Laura Beccera, 2019, original scientific article

Abstract: We propose that the inner engine of a type I binary-driven hypernova (BdHN) is composed of Kerr black hole (BH) in a non-stationary state, embedded in a uniform magnetic field B_0 aligned with the BH rotation axis and surrounded by an ionized plasma of extremely low density of 10^−14 g cm−3. Using GRB 130427A as a prototype, we show that this inner engine acts in a sequence of elementary impulses. Electrons accelerate to ultrarelativistic energy near the BH horizon, propagating along the polar axis, θ = 0, where they can reach energies of ~10^18 eV, partially contributing to ultrahigh-energy cosmic rays. When propagating with $\theta \ne 0$ through the magnetic field B_0, they produce GeV and TeV radiation through synchroton emission. The mass of BH, M = 2.31M ⊙, its spin, α = 0.47, and the value of magnetic field B_0 = 3.48 × 10^10 G, are determined self consistently to fulfill the energetic and the transparency requirement. The repetition time of each elementary impulse of energy ${ \mathcal E }\sim {10}^{37}$ erg is ~10^−14 s at the beginning of the process, then slowly increases with time evolution. In principle, this "inner engine" can operate in a gamma-ray burst (GRB) for thousands of years. By scaling the BH mass and the magnetic field, the same inner engine can describe active galactic nuclei.
Keywords: black hole physics, binaries, gamma-ray burst, neutron stars, supernovae, Astrophysics - High Energy Astrophysical Phenomena
Published in RUNG: 20.07.2020; Views: 2967; Downloads: 0
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5.
Exploring the Universe with supernovae
Tanja Petrushevska, published scientific conference contribution abstract (invited lecture)

Abstract: Supernovae have proven to be exquisite tools for a variety of astrophysics and cosmology topics. In this lecture, I will highlight a selection of dedicated tele- scopic surveys for detecting supernovae and I will report some of our interesting discoveries during the past few years. I will dedicate special attention to strongly lensed supernovae by galaxies and galaxy clusters. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. Therefore, measuring time delays from strongly lensed supernovae is emerging as a novel and independent tool for estimating the Hubble constant (H0). This is very important given the recent discord in the value of H0 from two methods that probe different distance ranges: the ESA mission Planck value corresponds to 67.74 ± 0.46 km s−1 Mpc−1; [1], while a reanalysis of the local distance scale gives 73.24 ± 1.74 km s−1 Mpc−1; [2, 3], these measurements thus being inconsistent at the ≈ 3.5σ level. Therefore, the results of additional independent and high- precision techniques, which rely on different physics, are of key importance. In this context, I will report our discovery of the first resolved multiply-imaged gra- vitationally lensed supernova Type Ia [4]. Moving forward, I will discuss some of the prospects of upcoming facilities such as the Large Synoptic Survey Telescope and James Webb Space Telescope [5, 6].
Keywords: supernovae, strong lensing, neutron stars
Published in RUNG: 29.11.2018; Views: 3122; Downloads: 0
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6.
A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary
Tanja Petrushevska, 2018, original scientific article

Abstract: Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
Keywords: supernova, neutron stars, gravitational waves
Published in RUNG: 12.10.2018; Views: 3439; Downloads: 0
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