17 research outputs found
Comparison of different Tidal Disruption Event light curve models with TiDE, a new modular open source code
A tidal disruption event (TDE) occurs when a supermassive black hole disrupts
a nearby passing star by tidal forces. The subsequent fallback accretion of the
stellar debris results in a luminous transient outburst. Modeling the light
curve of such an event may reveal important information, for example the mass
of the central black hole. This paper presents the TiDE software based on
semi-analytic modeling of TDEs. This object-oriented code contains different
models for the accretion rate and the fallback timescale . We
compare the resulting accretion rates to each other and with hydrodynamically
simulated ones and find convincing agreement for full disruptions. We present a
set of parameters estimated with TiDE for the well-observed TDE candidate
AT2019qiz, and compare our results with those given by the MOSFiT code. Most of
the parameters are in reasonable agreement, except for the mass and the
radiative efficiency of the black hole, both of which depend heavily on the
adopted fallback accretion rate.Comment: 17 pages, 12 figures, 2 tables, accepted in PAS
Fitting optical light curves of Tidal Disruption Events with TiDE
A Tidal Disruption Event (TDE) occurs when a supermassive black hole tidally
disrupt a nearby passing star. The fallback accretion rate of the disrupted
star may exceed the Eddington limit, which induces a supersonic outflow and a
burst of luminosity, similar to an explosive event. Thus, TDEs can be detected
as very luminous transients, and the number of observations for such events is
increasing rapidly. In this paper we fit 20 TDE light curves with TiDE, a new
public, object-oriented code designed to model optical TDE light curves. We
compare our results with those obtained by the popular MOSFiT and the recently
developed TDEmass codes, and discuss the possible sources of differences.Comment: 14 pages, 4 figures, 4 tables, accepted in PAS
Initial 56Ni Masses in Type Ia Supernovae
We infer initial masses of the synthesized radioactive nickel-56 in a sample
of recent Type Ia supernovae applying a new formalism introduced recently by
Khatami & Kasen (2019). It is shown that the nickel masses we derive do not
differ significantly from previous estimates based on the traditional
Arnett-model. We derive the parameter for our sample SNe and show that
these are consistent with the fiducial value of given by Khatami &
Kasen (2019) from SN Ia hydrodynamical simulations.Comment: 7 pages, 6 figures, published in PAS
Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct
Funding: This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No. 716155 (SACCRED) and from the "Transient Astrophysical Objects" GINOP 2.3.2-15-2016-00033 project of the National Research, Development and Innovation Office (NKFIH), Hungary, funded by the European Union. We acknowledge support from ESA PRODEX contract No. 4000132054. Zs.N., L.K., and K.V. acknowledge the support by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. K.V. is supported by the Bolyai+ grant UNKP-22-5-ELTE-1093. This project has been supported by the K-131508 grant of the Hungarian National Research, Development and Innovation Office (NKFIH) and the Élvonal grant KKP-143986. Authors acknowledge the financial support of the Austrian-Hungarian Action Foundation (101.u13, 104.u2). L.K. acknowledges the financial support of the Hungarian National Research, Development and Innovation Office grant NKFIH PD-134784. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON-RadioNet Pilot).Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined two classes. We present the analyses of light curves, color variations, spectral lines, and CO modeling. The light curves show at least five brightening events since 2015, and the multifilter color evolutions are mostly gray. The gray evolution indicates that bursts are triggered by mechanisms other than extinction. Our near-infrared spectra exhibit both absorption and emission lines and show time variability throughout our observations. We found lower rotational velocity and lower temperature from the near-infrared atomic absorption lines than from the optical lines, suggesting that Gaia19fct has a Keplerian rotating disk. The CO overtone features show a superposition of absorption and emission components, which is unlike other young stellar objects. We modeled the CO lines, and the result suggests that the emission and absorption components are formed in different regions. We found that although Gaia19fct exhibits characteristics of both types of eruptive young stars, FU Orionis–type objects and EX Lupi–type objects, it shows more similarity with EXors in general.Publisher PDFPeer reviewe
Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No. 716155 (SACCRED) and from the "Transient Astrophysical Objects" GINOP 2.3.2-15-2016-00033 project of the National Research, Development and Innovation Office (NKFIH), Hungary, funded by the European Union. We acknowledge support from ESA PRODEX contract No. 4000132054. Zs.N., L.K., and K.V. acknowledge the support by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. K.V. is supported by the Bolyai+ grant UNKP-22-5-ELTE-1093. This project has been supported by the K-131508 grant of the Hungarian National Research, Development and Innovation Office (NKFIH) and the Élvonal grant KKP-143986. Authors acknowledge the financial support of the Austrian-Hungarian Action Foundation (101.u13, 104.u2). L.K. acknowledges the financial support of the Hungarian National Research, Development and Innovation Office grant NKFIH PD-134784. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON-RadioNet Pilot).Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined two classes. We present the analyses of light curves, color variations, spectral lines, and CO modeling. The light curves show at least five brightening events since 2015, and the multifilter color evolutions are mostly gray. The gray evolution indicates that bursts are triggered by mechanisms other than extinction. Our near-infrared spectra exhibit both absorption and emission lines and show time variability throughout our observations. We found lower rotational velocity and lower temperature from the near-infrared atomic absorption lines than from the optical lines, suggesting that Gaia19fct has a Keplerian rotating disk. The CO overtone features show a superposition of absorption and emission components, which is unlike other young stellar objects. We modeled the CO lines, and the result suggests that the emission and absorption components are formed in different regions. We found that although Gaia19fct exhibits characteristics of both types of eruptive young stars, FU Orionis–type objects and EX Lupi–type objects, it shows more similarity with EXors in general.Publisher PDFPeer reviewe
Hypoalbuminemia affects one third of acute pancreatitis patients and is independently associated with severity and mortality
The incidence and medical costs of acute pancreatitis (AP) are on the rise, and severe cases still have a 30% mortality rate. We aimed to evaluate hypoalbuminemia as a risk factor and the prognostic value of human serum albumin in AP. Data from 2461 patients were extracted from the international, prospective, multicentre AP registry operated by the Hungarian Pancreatic Study Group. Data from patients with albumin measurement in the first 48 h (n = 1149) and anytime during hospitalization (n = 1272) were analysed. Multivariate binary logistic regression and Receiver Operator Characteristic curve analysis were used. The prevalence of hypoalbuminemia (< 35 g/L) was 19% on admission and 35.7% during hospitalization. Hypoalbuminemia dose-dependently increased the risk of severity, mortality, local complications and organ failure and is associated with longer hospital stay. The predictive value of hypoalbuminemia on admission was poor for severity and mortality. Severe hypoalbuminemia (< 25 g/L) represented an independent risk factor for severity (OR 48.761; CI 25.276-98.908) and mortality (OR 16.83; CI 8.32-35.13). Albumin loss during AP was strongly associated with severity (p < 0.001) and mortality (p = 0.002). Hypoalbuminemia represents an independent risk factor for severity and mortality in AP, and it shows a dose-dependent relationship with local complications, organ failure and length of stay.Peer reviewe
Photometric and Spectroscopic Properties of Type Ia Supernova 2018oh with Early Excess Emission from the Kepler 2 Observations
Supernova (SN) 2018oh (ASASSN-18bt) is the first spectroscopically- confirmed type Ia supernova (SN Ia) observed in the field. The data revealed an excess emission in its early light curve, allowing to place interesting constraints on its progenitor system (Dimitriadis et al. 2018, Shappee et al. 2018b). Here, we present extensive optical, ultraviolet, and near-infrared photometry, as well as dense sampling of optical spectra, for this object. SN 2018oh is relatively normal in its photometric evolution, with a rise time of 18.30.3 days and m0.03 mag, but it seems to have bluer colors. We construct the "uvoir" bolometric light curve having peak luminosity as 1.4910erg s, from which we derive a nickel mass as 0.550.04M by fitting radiation diffusion models powered by centrally located Ni. Note that the moment when nickel-powered luminosity starts to emerge is +3.85 days after the first light in the Kepler data, suggesting other origins of the early-time emission, e.g., mixing of Ni to outer layers of the ejecta or interaction between the ejecta and nearby circumstellar material or a non-degenerate companion star. The spectral evolution of SN 2018oh is similar to that of a normal SN Ia, but is characterized by prominent and persistent carbon absorption features. The C II features can be detected from the early phases to about 3 weeks after the maximum light, representing the latest detection of carbon ever recorded in a SN Ia. This indicates that a considerable amount of unburned carbon exists in the ejecta of SN 2018oh and may mix into deeper layers
K2 Observations of SN 2018oh Reveal a Two-component Rising Light Curve for a Type Ia Supernova
We present an exquisite 30 minute cadence Kepler (K2) light curve of the Type Ia supernova (SN Ia) 2018oh (ASASSN-18bt), starting weeks before explosion, covering the moment of explosion and the subsequent rise, and continuing past peak brightness. These data are supplemented by multi- color Panoramic Survey Telescope (Pan-STARRS1) and Rapid Response System 1 and Cerro Tololo Inter-American Observatory 4 m Dark Energy Camera (CTIO 4-m DECam) observations obtained within hours of explosion. The K2 light curve has an unusual two-component shape, where the flux rises with a steep linear gradient for the first few days, followed by a quadratic rise as seen for typical supernovae (SNe) Ia. This “flux excess” relative to canonical SN Ia behavior is confirmed in our i-band light curve, and furthermore, SN 2018oh is especially blue during the early epochs. The flux excess peaks 2.14 ± 0.04 days after explosion, has a FWHM of 3.12 ± 0.04 days, a blackbody temperature of T=17,{500}-9,000+11,500 K, a peak luminosity of 4.3+/- 0.2× {10}37 {erg} {{{s}}}-1, and a total integrated energy of 1.27+/- 0.01× {10}43 {erg}. We compare SN 2018oh to several models that may provide additional heating at early times, including collision with a companion and a shallow concentration of radioactive nickel. While all of these models generally reproduce the early K2 light curve shape, we slightly favor a companion interaction, at a distance of ∼2× {10}12 {cm} based on our early color measurements, although the exact distance depends on the uncertain viewing angle. Additional confirmation of a companion interaction in future modeling and observations of SN 2018oh would provide strong support for a single-degenerate progenitor system