A two-component model for fitting light-curves of core-collapse supernovae

We present an improved version of a light curve model, which is able to estimate the physical properties of different types of core-collapse supernovae having double-peaked light curves, in a quick and efficient way. The model is based on a two-component configuration consisting of a dense, inner region and an extended, low-mass envelope. Using this configuration, we estimate the initial parameters of the progenitor via fitting the shape of the quasi-bolometric light curves of 10 SNe, including Type IIP and IIb events, with model light curves. In each case we compare the fitting results with available hydrodynamic calculations, and also match the derived expansion velocities with the observed ones. Furthermore, we also compare our calculations with hydrodynamic models derived by the SNEC code, and examine the uncertainties of the estimated physical parameters caused by the assumption of constant opacity and the inaccurate knowledge of the moment of explosion

Photospheric Velocity Gradients and Ejecta Masses of Hydrogen-poor Superluminous Supernovae -- Proxies for Distinguishing between Fast and Slow Events

We present a study of 28 Type I superluminous supernovae (SLSNe) in the context of the ejecta mass and photospheric velocity. We combine photometry and spectroscopy to infer ejecta masses via the formalism of radiation diffusion equations. We show an improved method to determine the photospheric velocity by combining spectrum modeling and cross correlation techniques. We find that Type I SLSNe can be divided into two groups by their pre-maximum spectra. Members of the first group have the W-shaped absorption trough in their pre-maximum spectrum, usually identified as due to O II. This feature is absent in the spectra of supernovae in the second group, whose spectra are similar to SN~2015bn. We confirm that the pre- or near-maximum photospheric velocities correlate with the velocity gradients: faster evolving SLSNe have larger photosheric velocities around maximum. We classify the studied SLSNe into the Fast or the Slow evolving group by their estimated photosheric velocities, and find that all those objects that resemble to SN~2015bn belong to the Slow evolving class, while SLSNe showing the W-like absorption are represented in both Fast and Slow evolving groups. We estimate the ejecta masses of all objects in our sample, and obtain values in the range of 2.9 ($\pm$0.8) - 208 ($\pm$61) $M_\odot$, with a mean of $43 (\pm 12)~ M_\odot$. We conclude that Slow evolving SLSNe tend to have higher ejecta masses compared to the Fast ones. Our ejecta mass calculations suggests that SLSNe are caused by energetic explosions of very massive stars, irrespectively of the powering mechanism of the light curve.Comment: 21 pages, Submitted to Ap

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

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 $t_{\rm min}$. 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

Double neutron star formation via consecutive type II supernova explosions

Since the discovery of the first double neutron star (DNS) system, the number of these exotic binaries has reached fifteen. Here we investigate a channel of DNS formation in binary systems with components above the mass limit of type II supernova explosion (SN II), i.e. 8 MSun. We apply a spherically symmetric homologous envelope expansion model to account for mass loss, and follow the dynamical evolution of the system numerically with a high-precision integrator. The first SN occurs in a binary system whose orbital parameters are pre-defined, then, the homologous expansion model is applied again in the newly formed system. Analysing 1 658 880 models we find that DNS formation via subsequent SN II explosions requires a fine-tuning of the initial parameters. Our model can explain DNS systems with a separation greater than 2.95 au. The eccentricity of the DNS systems spans a wide range thanks to the orbital circularisation effect due to the second SN II explosion. The eccentricity of the DNS is sensitive to the initial eccentricity of the binary progenitor and the orbital position of the system preceding the second explosion. In agreement with the majority of the observations of DNS systems, we find the system centre-of mass velocities to be less than 60 km/s. Neutron stars that become unbound in either explosion gain a peculiar velocity in the range of 0.02 - 240 km/s. In our model, the formation of tight DNS systems requires a post-explosion orbit-shrinking mechanism, possibly driven by the ejected envelopes.Comment: Accepted for publication in MNRA

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 $\beta$ parameter for our sample SNe and show that these are consistent with the fiducial value of $\sim 1.6$ given by Khatami & Kasen (2019) from SN Ia hydrodynamical simulations.Comment: 7 pages, 6 figures, published in PAS

Detection and Classification of Supernovae Beyond Z ∼ 2 Redshift with the James Webb Space Telescope

Future time-domain surveys for transient events in the near- and midinfrared bands will significantly extend our understanding about the physics of the early universe. In this paper we study the implications of a deep (˜27 mag), long-term (˜3 yr), observationally inexpensive survey with the James Webb Space Telescope (JWST) within its Continuous Viewing Zone, aimed at discovering luminous supernovae beyond z ˜ 2 redshift. We explore the possibilities for detecting superluminous supernovae (SLSNe) as well as SNe Ia at such high redshifts and estimate their expected numbers within a relatively small (˜0.1 deg2) survey area. It is found that we can expect ˜10 new SLSNe and ˜50 SNe Ia discovered in the 1 < z < 4 redshift range. We show that it is possible to get relatively accurate (σ z ≲ 0.25) photometric redshifts for SNe Ia by fitting their Spectral Energy Distributions, redshifted into the observed near-IR bands, with SN templates. We propose that SNe Ia occupy a relatively narrow range on the JWST F220W-F440W versus F150W-F356W color-color diagram between ±7 rest-frame days around maximum light, which could be a useful classification tool for such types of transients. We also study the possibility of extending the Hubble-diagram of SNe Ia beyond redshift 2 up to z ˜ 4. Such high-z SNe Ia may provide new observational constraints for their progenitor scenario

Detecting Pair-instability Supernovae at z ≲ 5 with the James Webb Space Telescope

Pair-instability supernovae (PISNe) are the ultimate cosmic lighthouses, capable of being observed at z ≳ 25 and revealing the properties of primordial stars at cosmic dawn. But it is now understood that the spectra and light curves of these events evolved with redshift as the universe became polluted with heavy elements because chemically enriched stars in this mass range typically lose most of their hydrogen envelopes and explode as bare helium cores. The light curves of such transients can be considerably dimmer in the near-infrared today than those of primordial PISNe of equal energy and progenitor mass. Here, we calculate detection rates for PISNe whose progenitors lost their outer layers to either line-driven winds or rotation at z ≲ 10, their detection limit in redshift for the James Webb Space Telescope (JWST). We find that JWST may be able to detect only Population II (metal-poor) PISNe over the redshift range of z ≲ 4, but not their Population III (metal-free) counterparts

The Purport of Space Telescopes in Supernova Research

The violent stellar explosions known as supernovae have received especially strong attention in both the research community and the general public recently. With the advent of space telescopes, the study of these extraordinary events has switched gears and it has become one of the leading fields in modern astrophysics. In this paper, we review some of the recent developments, focusing mainly on studies related to space-based observations