arXiv subjects

Melina Bersten

Publications and source records attributed to Melina Bersten.

7 recordsLinked to original sources

arXiv2025

Rapid follow-up observations of infant supernovae with the Gran Telescopio Canarias

The first few hours of a supernova (SN) contain significant information about the progenitor system. The most modern wide-field surveys that scan the sky repeatedly every few days can discover all kinds of transients in those early epochs. At such times, some progenitor footprints may be visible, elucidating critical explosion parameters and helping to distinguish between leading explosion models. A dedicated spectroscopic classification programme using the optical spectrograph OSIRIS mounted on the Gran Telescopio Canarias was set up to try to obtain observations of supernovae (SNe) at those early epochs. With the time awarded, we obtained spectra of 10 SN candidates, which we present here. Half of them were thermonuclear SNe, while the other half were core-collapse SNe. Most (70\%) were observed within the first six days of the estimated explosion, with two being captured within the first 48\,hr. We present a characterization of the spectra, together with other public ancillary photometry from the Zwicky Transient Facility (ZTF) and the Asteroid Terrestrial-impact Last Alert System (ATLAS). This project shows the need for an accompanying rapid-response spectroscopic programme for existing and future deep photometric wide-field surveys located at the right longitude to be able to trigger observations in a few hours after the discovery of the SN candidate.

astro-ph.SR↗

arXiv2024

The metamorphosis of the Type Ib SN 2019yvr: late-time interaction

We present observational evidence of late-time interaction between the ejecta of the hydrogen-poor Type Ib supernova (SN) 2019yvr and hydrogen-rich circumstellar material (CSM), similar to the Type Ib SN 2014C. A narrow Hα emission line appears simultaneously with a break in the light-curve decline rate at around 80-100 d after explosion. From the interaction delay and the ejecta velocity, under the assumption that the CSM is detached from the progenitor, we estimate the CSM inner radius to be located at ~6.5-9.1 {\times} 10^{15} cm. The Hα emission line persists throughout the nebular phase at least up to +420 d post-explosion, with a full width at half maximum of ~2000 km/s. Assuming a steady mass-loss, the estimated mass-loss rate from the luminosity of the Hα line is ~3-7 {\times} 10^{-5} M_\odot yr^{-1}. From hydrodynamical modelling and analysis of the nebular spectra, we find a progenitor He-core mass of 3-4 M{_\odot}, which would imply an initial mass of 13-15 M{_\odot}. Our result supports the case of a relatively low-mass progenitor possibly in a binary system as opposed to a higher mass single star undergoing a luminous blue variable phase.

astro-ph.HE↗

arXiv2022

Supernovae double-peaked light curves from double-nickel distribution

Among supernovae (SNe) of different luminosities, many double-peaked light curves (LCs) have been observed, representing a broad morphological variety. In this work, we investigate which of these can be modelled by assuming a double-peaked distribution of their radioactive material, as originally proposed for SN2005bf. The inner zone corresponds to the regular explosive nucleosynthesis and extends outwards, according to the usual scenario of mixing. The outer 56Ni-rich shell may be related to the effect of jet-like outflows that have interacted with more distant portions of the star before the arrival of the SN shock. As the outer layer is covered by matter that is optically less thick, its energy emerges earlier and generates a first peak of radiation. To investigate this scenario in more detail, we have applied our hydrodynamic code that follows the shock propagation through the progenitor star and takes into account the effect of the gamma-ray photons produced by the decay of the radioactive isotopes. We present a simple parametric model for the 56Ni abundance profile and explore the consequences on the LC of individually varying the quantities that define this distribution, setting our focus onto the stripped-envelope progenitors. In this first study, we are interested in the applicability of this model to SNe that have not been classified as superluminous, thus, we have selected our parameter space accordingly. Then, within the same mathematical prescription for the 56Ni-profile, we revisited the modelling process for a series of objects: SN2005bf, PTF2011mnb, SN2019cad, and SN2008D. In some cases, a decrease in the gamma ray opacity is required to fit the late time observations. We also discuss the other cases in which this scenario might be likely to explain the LC morphology.

astro-ph.SR↗

arXiv2018

A systematic study of magnetar-powered hydrogen-rich supernovae

Context: It has been suggested that some supernovae (SNe) may be powered by a magnetar formed at the moment of the explosion. While this scenario has mostly been applied to hydrogen-free events, it may be possible also for hydrogen-rich objects. Aims: We explore the effect of including a magnetar on the light curves of supernovae with H-rich progenitors. Methods: We have applied a version of our one-dimensional LTE radiation hydrodynamics code that takes into account the relativistic motion of the ejecta caused by the extra energy provided by the magnetar. For a fixed red supergiant (RSG) progenitor, we have obtained a set of light curves that corresponds to different values of the magnetar initial rotation energy and the spin-down timescale. The model is applied to SN~2004em and OGLE-2014-SN-073, two peculiar Type II SNe with long-rising SN1987A-like light curves, although with much larger luminosities. Results: The presence of a plateau phase in either normal or superluminous supernovae is one possible outcome, even if a magnetar is continuously injecting energy into the ejecta.In other cases, the light curve shows a peak but not a plateau. Also, there are intermediate events with a first peak followed by a slow decline and a late break of the declining slope. Our models show that bright and long rising morphologies are possible even assuming RSG structures. Conclusions: A large number of supernova discoveries per year reveal unexpected new types of explosions. According to our results, SLSNe II-P are to be expected, as well as a variety of light curve morphologies that can all be possible signs of a newly born magnetar.

astro-ph.HE↗

arXiv2013

Extraordinary Magnification of the Ordinary Type Ia Supernova PS1-10afx

Recently, Chornock and co-workers announced the Pan-STARRS discovery of a transient source reaching an apparent peak luminosity of ~4x10^44 erg s^-1. We show that the spectra of this transient source are well fit by normal Type Ia supernova (SNIa) templates. The multi-band colors and light-curve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z=1.3883; however, the observed flux is a constant factor of ~30 times too bright in each band over time as compared to the templates. At minimum, this shows that the peak luminosities inferred from the light-curve widths of some SNeIa will deviate significantly from the established, empirical relation used by cosmologists. We argue on physical grounds that the observed fluxes do not reflect an intrinsically luminous SNIa, but rather PS1-10afx is a normal SNIa whose flux has been magnified by an external source. The only known astrophysical source capable of such magnification is a gravitational lens. Given the lack of obvious lens candidates, such as galaxy clusters, in the vicinity, we further argue that the lens is a supermassive black hole or a comparatively low-mass dark matter halo. In this case, the lens continues to magnify the underlying host galaxy light. If confirmed, this discovery could impact a broad range of topics including cosmology, gamma-ray bursts, and dark matter halos.

astro-ph.CO↗

arXiv2010

The Standardized Candle Method for Type II Plateau Supernovae

In this paper we study the "standardized candle method" using a sample of 37 nearby (z<0.06) Type II plateau supernovae having BVRI photometry and optical spectroscopy. An analytic procedure is implemented to fit light curves, color curves, and velocity curves. We find that the V-I color toward the end of the plateau can be used to estimate the host-galaxy reddening with a precision of 0.2 mag. The correlation between plateau luminosity and expansion velocity previously reported in the literature is recovered. Using this relation and assuming a standard reddening law (Rv = 3.1), we obtain Hubble diagrams in the BVI bands with dispersions of ~0.4 mag. Allowing Rv to vary and minimizing the spread in the Hubble diagrams, we obtain a dispersion range of 0.25-0.30 mag, which implies that these objects can deliver relative distances with precisions of 12-14%. The resulting best-fit value of Rv is 1.4 +/- 0.1.

astro-ph.CO↗

arXiv2005

Testing a string dilaton model with experimental and observational data

We test the prediction of the time variation of the fine structure constant in the string dilaton model proposed by Damour and Polyakov. First, we analize the dependence of all available observational and experimental data with the fine structure constant variation. Furthermore, we obtain the prediction of the time variation of the fine structure constant including the renormalization group correction. Finally, we use the data set to perform a statistical analyisis. This analysis enables us to determine that the the dilaton model is in agreement with most of the data. Finally, constraints on the free parameters of this model are obtained.

astro-ph↗