arXiv subjects

N. Elias-Rosa

Publications and source records attributed to N. Elias-Rosa.

At least 37 records · Page 2Linked to original sources

arXiv2025

Explosion sites of SN 1994W-like transients

We study a sample of narrow-line transients that share characteristics with the Type IIn classified supernova (SN) 1994W, a prototypical member of this class of events, via investigation of their explosion sites and spectrophotometric data. The normalised cumulative rank (NCR) method was used to compare the explosion sites of 10 events to the star-formation distributions of their host galaxies, and to the sites of different evolved massive stars. The resulting sample mean value of NCR$_{\mathrm{H}α} = 0.170 \pm 0.076$ is low, while the NCR$_{\mathrm{NUV}}$ distribution is flat with a mean value of $0.488 \pm 0.084$. The NCR distribution of SN 1994W-like events is consistent with relatively low-mass red supergiants (RSGs) and, despite the small sample size, inconsistent with high-mass stars such as luminous blue variables. To explain the nature of SN 1994W-like transients, interaction between an expanding ejecta and a relatively massive circumstellar medium is likely required, with the latter possibly having been produced by a H envelope ejection via a nuclear flash event, or a luminous red nova (LRN) from a stellar merger; both channels are consistent with low-mass RSGs suggested by the NCR results. In this context, we find the early $-26$ d spectrum from light curve maximum of SN 2003G to share similarities to those of F8-type supergiant stars and LRNe. Finally, based on late-time HST imaging, we set the deepest limits for the surviving precursor of SN 2011ht to $M_{\mathrm{F438W}} > -3.8$ and $M_{\mathrm{F555W}} > -4.0$ mag. This would exclude most supergiants as a non-terminal progenitor, assuming that such a star is not completely obscured by newly formed dust.

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arXiv2025

Expanding the parameter space of 2002es-like type Ia supernovae: on the underluminous ASASSN-20jq / SN 2020qxp

We present optical photometric and spectroscopic observations of the peculiar Type Ia supernova ASASSN-20jq/SN 2020qxp. It is a low-luminosity object with a peak absolute magnitude of $M_B=-17.1\pm0.5$ mag. Despite its low luminosity, its post-peak light-curve decline rate ($Δm_{15}(B)=1.35\pm0.09$ mag) and color-stretch parameter (sBV>0.82) are similar to normal SNe Ia, making it an outlier in the luminosity-width and luminosity-color-stretch relations. Early light curves suggest a "bump" during the first 1.4 days of explosion. ASASSN-20jq synthesized a low radioactive $^{56}$Ni mass of $0.09\pm0.01M_\odot$. Near-maximum light spectra reveal strong Si II absorption lines, indicating a cooler photosphere than normal SNe Ia, but lack Ti II absorption lines. Unusually strong O I $λ$7773 and Ca II near-infrared triplet absorption features are present. Nebular spectra show a strong, narrow forbidden [Ca II] $λλ$7291,7324 doublet emission, rarely seen in SNe Ia except in some Type Iax events. Marginal detection of [O I] $λλ$6300,6364 doublet emission, which is extremely rare, is observed. Both [Ca II] and [O I] lines are redshifted by $\sim2000$ km/s. A strong [Fe II] $λ$7155 emission line with a tilted-top profile, identical to the [Fe II] $λ$16433 profile, is also observed. These asymmetric [Fe II] profiles and redshifted [Ca II] and [O I] emissions suggest a high central density white dwarf progenitor undergoing an off-center delayed-detonation explosion mechanism, producing roughly equal amounts of $^{56}$Ni in deflagration and detonation phases. This distinguishes ASASSN-20jq from normal and subluminous SNe Ia. ASASSN-20jq's light curve and spectra do not align with any single SNe Ia subclass but show similarities to 2002es-like objects. Thus, we add it as an extreme candidate within the heterogeneous parameter space of 2002es-like SNe Ia.

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arXiv2025

The bright long-lived Type II SN 2021irp powered by aspherical circumstellar material interaction (I): Revealing the energy source with photometry and spectroscopy

Some core-collapse supernovae (CCSNe) are too luminous and radiate too much total energy to be powered by the release of thermal energy from the ejecta and radioactive-decay energy from the synthesised $^{56}$Ni/$^{56}$Co. A source of additional power is the interaction between the supernova (SN) ejecta and a massive circumstellar material (CSM). This is an important power source in Type IIn SNe, which show narrow spectral lines arising from the unshocked CSM, but not all interacting SNe show such narrow lines. We present photometric and spectroscopic observations of the hydrogen-rich SN 2021irp, which is both luminous, with $M_{o} < -19.4$ mag, and long-lived, remaining brighter than $M_{o} = -18$ mag for $\sim$ 250 d. We show that an additional energy source is required to power such a SN, and determine the nature of the source. We also investigate the properties of the pre-existing and newly formed dust associated with the SN. Photometric observations show that the luminosity of the SN is an order of magnitude higher than typical Type II SNe and persists for much longer. We detect a infrared excess attributed to dust emission. Spectra show multi-component line profiles, an Fe II pseudo-continuum, and a lack of absorption lines, all typical features of Type IIn SNe. We detect a narrow (< 85 kms$^{-1}$) P-Cygni profile associated with the unshocked CSM. An asymmetry in emission line profiles indicates dust formation occurring from 250-300 d. Analysis of the SN blackbody radius evolution indicates asymmetry in the shape of the emitting region. We identify the main power source of SN 2021irp as extensive interaction with a massive CSM, and that this CSM is distributed asymmetrically around the progenitor star. The infrared excess is explained with emission from newly formed dust although there is also some evidence of an IR echo from pre-existing dust at early times.

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arXiv2025

The bright long-lived Type II SN 2021irp powered by aspherical circumstellar material interaction (II): Estimating the CSM mass and geometry with polarimetry and light curve modeling

There is evidence for interaction between supernova (SN) ejecta and massive circumstellar material (CSM) in various types of SNe. The mass-ejection mechanisms that produce massive CSM are unclear, and studying interacting SNe and their CSM can shed light on these mechanisms and the final stages of stellar evolution. We aim to study the properties of the CSM in the bright, long-lived, hydrogen-rich (Type II) SN 2021irp, which is interacting with a massive aspherical CSM. We present imaging- and spectro-polarimetric observations of SN 2021irp. By modelling its polarisation and bolometric light curve, we derive the mass and distribution of the CSM. SN 2021irp shows a high intrinsic polarisation of $\sim0.8$%. This high continuum polarisation suggests an aspherical photosphere created by an aspherical CSM interaction. Based on the bolometric light curve evolution and the high polarization, SN 2021irp can be explained as a typical Type II SN interacting with a CSM disk with a corresponding mass-loss rate and half-opening angle of $\sim0.035$ - $0.1$ M$_{\odot}$ yr$^{-1}$ and $\sim30$ - $50^{\circ}$, respectively. The total CSM mass derived is $\gtrsim 2$ M$_{\odot}$. We suggest that this CSM disk was created by some process related to binary interaction, and that SN 2021irp is the end product of a typical massive star (i.e. with Zero-Age-Main-Sequence mass of $\sim 8-18$ M$_{\odot}$) that has a separation and/or mass ratio with its companion star that led to an extreme mass ejection within decades of explosion. Based on the observational properties of SN 2021irp and similar SNe, we propose a general picture for the spectroscopic properties of Type II SNe interacting with a massive disk CSM.

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arXiv2025

On the diversity of strongly-interacting Type IIn supernovae

Massive stars experience strong mass-loss, producing a dense, H-rich circumstellar medium (CSM). After the explosion, the collision and continued interaction of the supernova (SN) ejecta with the CSM power the light curve through the conversion of kinetic energy into radiation. When the interaction is strong, the light curve shows a broad peak and high luminosity lasting for a relatively long time. Also the spectral evolution is slower, compared to non-interacting SNe. Energetic shocks between the ejecta and the CSM create the ideal conditions for particle acceleration and production of high-energy (HE) neutrinos above 1 TeV. In this paper, we study four strongly-interacting Type IIn SNe: 2021acya, 2021adxl, 2022qml, and 2022wed to highlight their peculiar characteristics, derive the kinetic energy of the explosion and the characteristics of the CSM, infer clues on the possible progenitors and their environment and relate them to the production of HE neutrinos. The SNe analysed in this sample exploded in dwarf, star-forming galaxies and they are consistent with energetic explosions and strong interaction with the surrounding CSM. For SNe 2021acya and 2022wed, we find high CSM masses and mass-loss rates, linking them to very massive progenitors. For SN 2021adxl, the spectral analysis and less extreme CSM mass suggest a stripped-envelope massive star as possible progenitor. SN 2022qml is marginally consistent with being a Type Ia thermonuclear explosion embedded in a dense CSM. The mass-loss rates for all SNe are consistent with the expulsion of several solar masses of material during eruptive episodes in the last few decades before the explosion. Finally, we find that the SNe in our sample are marginally consistent with HE neutrino production.

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arXiv2025

SN 2018is: a low-luminosity Type IIP supernova with narrow hydrogen emission lines at early phases

We present a comprehensive photometric and spectroscopic study of the Type IIP SN 2018is. The $V$-band luminosity and the expansion velocity at 50 days post-explosion are $-$15.1$\pm$0.2 mag (corrected for A$_V$=1.34 mag) and 1400 km s$^{-1}$, classifying it as a low-luminosity SN II. The recombination phase in the $V$-band is shorter, lasting around 110 days, and exhibits a steeper decline (1.0 mag per 100 days) compared to most other low-luminosity SNe II. Additionally, the optical and near-infrared spectra display hydrogen emission lines that are strikingly narrow, even for this class. The Fe II and Sc II line velocities are at the lower end of the typical range for low-luminosity SNe II. Semi-analytical modelling of the bolometric light curve suggests an ejecta mass of $\sim$8 M$_\odot$, corresponding to a pre-supernova mass of $\sim$9.5 M$_\odot$, and an explosion energy of $\sim$0.40 $\times$ 10$^{51}$ erg. Hydrodynamical modelling further indicates that the progenitor had a zero-age main sequence mass of 9 M$_\odot$, coupled with a low explosion energy of 0.19 $\times$ 10$^{51}$ erg. The nebular spectrum reveals weak [O I] $λλ$6300,6364 lines, consistent with a moderate-mass progenitor, while features typical of Fe core-collapse events, such as He I, [C I], and [Fe I], are indiscernible. However, the redder colours and low ratio of Ni to Fe abundance do not support an electron-capture scenario either. As a low-luminosity SN II with an atypically steep decline during the photospheric phase and remarkably narrow emission lines, SN 2018is contributes to the diversity observed within this population.

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arXiv2024

Constraining the CSM structure and progenitor mass-loss history of interacting supernovae through 3D hydrodynamic modeling: The case of SN 2014C

We investigate SN 2014C using three-dimensional hydrodynamic modeling, focusing on its early interaction with dense circumstellar medium (CSM). Our objective is to uncover the pre-supernova (SN) CSM structure and constrain the progenitor star's mass-loss history prior to core collapse. Our comprehensive model traces the evolution from the progenitor star through the SN event and into the SN remnant (SNR) phase. We simulate the remnant's expansion over approximately 15 years, incorporating a CSM derived from the progenitor star's outflows through dedicated hydrodynamic simulations. Analysis reveals that the remnant interacted with a dense toroidal nebula extending from $4.3\times 10^{16}\,$cm to $1.5\times 10^{17}$ cm in the equatorial plane, with a thickness of approximately $1.2\times 10^{17}$ cm. The nebula's density peaks at approximately $3\times 10^6\,$cm$^{-3}$ at the inner boundary, gradually decreasing as $\approx r^{-2}$ at greater distances. This nebula formed due to intense mass-loss from the progenitor star between approximately 5000 and 1000 years before collapse. During this period, the maximum mass-loss rate reached about $8\times 10^{-4}\,M_{\odot}\,$yr$^{-1}$, ejecting $\approx 2.5\,M_{\odot}$ of stellar material into the CSM. Our model accurately reproduces Chandra and NuSTAR spectra, including the Fe K line, throughout the remnant's evolution. Notably, the Fe line is self-consistently reproduced, originating from shocked ejecta, with $\approx 0.05\,M_{\odot}$ of pure-Fe ejecta shocked during the remnant-nebula interaction. These findings suggest that the 3D geometry and density distribution of the CSM, as well as the progenitor star's mass-loss history, align with a scenario where the star was stripped through binary interaction, specifically common envelope evolution.

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arXiv2024

The fast rise of the unusual Type IIL/IIb SN 2018ivc

We present an analysis of the photometric and spectroscopic dataset of the Type II supernova (SN) 2018ivc in the nearby (10 Mpc) galaxy Messier 77. Thanks to the high cadence of the CHASE survey, we observed the SN rising very rapidly by nearly three magnitudes in five hours (or 18 mag d$^{-1}$). The $r$-band light curve presents four distinct phases: the maximum light is reached in just one day, then a first, rapid linear decline precedes a short-duration plateau. Finally, a long, slower linear decline lasted for one year. Following a radio rebrightening, we detected SN 2018ivc four years after the explosion. The early spectra show a blue, nearly featureless continuum, but the spectra evolve rapidly: after about 10 days a prominent H$α$ line starts to emerge, with a peculiar profile, but the spectra are heavily contaminated by emission lines from the host galaxy. He I lines, namely $λλ$5876,7065, are also strong. On top of the former, a strong absorption from the Na I doublet is visible, indicative of a non-negligible internal reddening. From its equivalent width, we derive a lower limit on the host reddening of $A_V\simeq1.5$ mag, while from the Balmer decrement and a match of the $B-V$ colour curve of SN 2018ivc to that of the comparison objects, a host reddening of $A_V\simeq3.0$ mag is obtained. The spectra are similar to those of SNe II, but with strong He lines. Given the peculiar light curve and spectral features, we suggest SN 2018ivc could be a transitional object between the Type IIL and Type IIb SNe classes. In addition, we found signs of interaction with circumstellar medium in the light curve, making SN 2018ivc also an interacting event. Finally, we modelled the early multi-band light curves and photospheric velocity of SN 2018ivc to estimate the explosion and CSM physical parameters.

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arXiv2024

Massive stars exploding in a He-rich circumstellar medium $-$ X. Flash spectral features in the Type Ibn SN 2019cj and observations of SN 2018jmt

We present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about 10 days, reaching an absolute peak magnitude of $M_g$(SN 2018jmt) = $-$19.07 $\pm$ 0.37 and $M_V$(SN 2019cj) = $-$18.94 $\pm$ 0.19 mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (600$-$1000 km~s$^{-1}$) He I lines with P-Cygni profile. At later epochs, the spectra become more similar to those of the prototypical SN Ibn 2006jc. At early phases, the spectra of SN 2019cj show flash ionisation emission lines of C III, N III and He II superposed on a blue continuum. These features disappear after a few days, and then the spectra of SN 2019cj evolve similarly to those of SN 2018jmt. The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We model the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either that expected for a canonical SN Ib ($\sim$ 2 M$_{\odot}$) or those from a massive WR star ($>$ $\sim$ 4 M$_{\odot}$), with the kinetic energy on the order of $10^{51}$ erg. The lower limit on the ejecta mass ($>$ $\sim$ 2 M$_{\odot}$) argues against a scenario involving a relatively low-mass progenitor (e.g., $M_{ZAMS}$ $\sim$ 10 M$_{\odot}$). We set a conservative upper limit of $\sim$0.1 M$_{\odot}$ for the $^{56}$Ni masses in both SNe. From the light curve modelling, we determine a two-zone CSM distribution, with an inner, flat CSM component, and an outer CSM with a steeper density profile. The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive, stripped-envelope (SE) stars.

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arXiv2024

A study in scarlet -- I. Photometric properties of a sample of Intermediate Luminosity Red Transients

We investigate the photometric characteristics of a sample of Intermediate Luminosity Red Transients (ILRTs), a class of elusive objects with peak luminosity between that of classical novae and standard supernovae. We present the multi-wavelength photometric follow-up of four ILRTs, namely NGC 300 2008OT-1, AT 2019abn, AT 2019ahd and AT 2019udc. Through the analysis and modelling of their spectral energy distribution and bolometric light curves we infer the physical parameters associated with these transients. All four objects display a single peaked light curve which ends in a linear decline in magnitudes at late phases. A flux excess with respect to a single black body emission is detected in the infrared domain for three objects in our sample, a few months after maximum. This feature, commonly found in ILRTs, is interpreted as a sign of dust formation. Mid infrared monitoring of NGC 300 2008OT-1 761 days after maximum allows us to infer the presence of $\sim$10$^{-3}$-10$^{-5}$ M$_{\odot}$ of dust, depending on the chemical composition and the grain size adopted. The late time decline of the bolometric light curves of the considered ILRTs is shallower than expected for $^{56}$Ni decay, hence requiring an additional powering mechanism. James Webb Space Telescope observations of AT 2019abn prove that the object has faded below its progenitor luminosity in the mid-infrared domain, five years after its peak. Together with the disappearance of NGC 300 2008OT-1 in Spitzer images seven years after its discovery, this supports the terminal explosion scenario for ILRTs. With a simple semi-analytical model we try to reproduce the observed bolometric light curves in the context of few M$_{\odot}$ of material ejected at few 10$^{3}$ km s$^{-1}$ and enshrouded in an optically thick circumstellar medium.

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arXiv2024

A study in scarlet -- II. Spectroscopic properties of a sample of Intermediate Luminosity Red Transients

We investigate the spectroscopic characteristics of Intermediate Luminosity Red Transients (ILRTs), a class of elusive objects with peak luminosity between that of classical novae and standard supernovae. We present the extensive optical and near-infrared (NIR) spectroscopic monitoring of four ILRTs, namely NGC 300 2008OT-1, AT 2019abn, AT 2019ahd and AT 2019udc. First we focus on the evolution of the most prominent spectral features observed in the low resolution spectra, then we discuss more in detail the high resolution spectrum collected for NGC 300 2008OT-1 with the Very Large Telescope equipped with UVES. Finally we analyse late time spectra of NGC 300 2008OT-1 and AT 2019ahd through comparisons with both synthetic and observed spectra. Balmer and Ca lines dominate the optical spectra, revealing the presence of slowly moving circumstellar medium (CSM) around the objects. The line luminosity of H$α$, H$β$ and Ca II NIR triplet presents a double peaked evolution with time, possibly indicative of interaction between fast ejecta and the slow CSM. The high resolution spectrum of NGC 300 2008OT-1 reveals a complex circumstellar environment, with the transient being surrounded by a slow ($\sim$30 km s$^{-1}$) progenitor wind. At late epochs, optical spectra of NGC 300 2008OT-1 and AT 2019ahd show broad ($\sim$2500 km s$^{-1}$) emission features at $\sim$6170 A and $\sim$7000 A which are unprecedented for ILRTs. We find that these lines originate most likely from the blending of several narrow lines, possibly of iron-peak elements.

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arXiv2024

Red eminence: The intermediate-luminosity red transient AT 2022fnm

We present results from a five-month-long observing campaign of the unusual transient AT 2022fnm, which displays properties common to both luminous red novae (LRNe) and intermediate-luminosity red transients (ILRTs). Although its photometric evolution is broadly consistent with that of LRNe, no second peak is apparent in its light curve, and its spectral properties are more reminiscent of ILRTs. It has a fairly rapid rise time of 5.3$\pm$1.5 d, reaching a peak absolute magnitude of $-12.7\pm$0.1 (in the ATLAS $o$ band). We find some evidence for circumstellar interaction, and a near-infrared excess becomes apparent at approximately +100 d after discovery. We attribute this to a dust echo. Finally, from an analytical diffusion toy model, we attempted to reproduce the pseudo-bolometric light curve and find that a mass of $\sim$4 M$_\odot$ is needed. Overall, the characteristics of AT 2022fnm are consistent with a weak stellar eruption or an explosion reminiscent of low-energy type IIP supernovae, which is compatible with expectations for ILRTs.

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arXiv2024

JWST NIRSpec+MIRI Observations of the nearby Type IIP supernova 2022acko

We present JWST spectral and photometric observations of the Type IIP supernova (SN) 2022acko at ~50 days past explosion. These data are the first JWST spectral observations of a core-collapse SN. We identify ~30 different H I features, other features associated with products produced from the CNO cycle, and s-process elements such as Sc II and Ba II. By combining the JWST spectra with ground-based optical and NIR spectra, we construct a full Spectral Energy Distribution from 0.4 to 25 microns and find that the JWST spectra are fully consistent with the simultaneous JWST photometry. The data lack signatures of CO formation and we estimate a limit on the CO mass of < 10^{-8} solar mass. We demonstrate how the CO fundamental band limits can be used to probe underlying physics during stellar evolution, explosion, and the environment. The observations indicate little mixing between the H envelope and C/O core in the ejecta and show no evidence of dust. The data presented here set a critical baseline for future JWST observations, where possible molecular and dust formation may be seen.

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arXiv2023

SN 2021gno: a Calcium-rich transient with double-peaked light curves

We present extensive ultraviolet (UV) and optical photometric and optical spectroscopic follow-up of supernova (SN)~2021gno by the "Precision Observations of Infant Supernova Explosions" (POISE) project, starting less than two days after the explosion. Given its intermediate luminosity, fast photometric evolution, and quick transition to the nebular phase with spectra dominated by [Ca~II] lines, SN~2021gno belongs to the small family of Calcium-rich transients. Moreover, it shows double-peaked light curves, a phenomenon shared with only four other Calcium-rich events. The projected distance from the center of the host galaxy is not as large as other objects in this family. The initial optical light-curve peaks coincide with a very quick decline of the UV flux, indicating a fast initial cooling phase. Through hydrodynamical modelling of the bolometric light curve and line velocity evolution, we found that the observations are compatible with the explosion of a highly-stripped massive star with an ejecta mass of $0.8\,M_\odot$ and a $^{56}$Ni mass of $0.024~M_{\odot}$. The initial cooling phase (first light curve peak) is explained by the presence of an extended circumstellar material comprising $\sim$$10^{-2}\,M_{\odot}$ with an extension of $1100\,R_{\odot}$. We discuss if hydrogen features are present in both maximum-light and nebular spectra, and its implications in terms of the proposed progenitor scenarios for Calcium-rich transients.

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arXiv2023

SN 2020bio: A Double-peaked, H-poor Type IIb Supernova with Evidence of Circumstellar Interaction

We present photometric and spectroscopic observations of SN 2020bio, a double-peaked Type IIb supernova (SN) discovered within a day of explosion, primarily obtained by Las Cumbres Observatory and Swift. SN 2020bio displays a rapid and long-lasting initial decline throughout the first week of its light curve, similarly to other well-studied Type IIb SNe. This early-time emission is thought to originate from the cooling of the extended outer hydrogen-rich (H-rich) envelope of the progenitor star that is shock heated by the SN explosion. We compare SN 2020bio to a sample of other double-peaked Type IIb SNe in order to investigate its progenitor properties. Analytical model fits to the early-time emission give progenitor radius ($\approx$ 100--1500 $R_\odot$) and H-rich envelope mass ($\approx$ 0.01--0.5 $M_\odot$) estimates that are consistent with other Type IIb SNe. However, SN 2020bio displays several peculiarities, including: (1) weak H spectral features indicating a greater amount of mass loss than other Type IIb progenitors; (2) an underluminous secondary light-curve peak that implies a small amount of synthesized $^{56}$Ni ($M_{\text{Ni}}$ $\approx$ 0.02 $M_\odot$); and (3) low-luminosity nebular [O I] and interaction-powered nebular features. These observations are more consistent with a lower-mass progenitor ($M_{\text{ZAMS}} \approx$ 12 $M_\odot$) that was stripped of most of its H-rich envelope before exploding. This study adds to the growing diversity in the observed properties of Type IIb SNe and their progenitors.

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arXiv2023

Hidden shock powering the peak of SN 2020faa

The link between the fate of the most massive stars and the resulting supernova (SN) explosion is still a matter of debate, in major part because of the ambiguity among light-curve powering mechanisms. When stars explode as SNe, the light-curve luminosity is typically sustained by a central engine (radioactive decay, magnetar spin-down, or fallback accretion). However, since massive stars eject considerable amounts of material during their evolution, there may be a significant contribution coming from interactions with the previously ejected circumstellar medium (CSM). Reconstructing the progenitor configuration at the time of explosion requires a detailed analysis of the long-term photometric and spectroscopic evolution of the related transient. In this paper, we present the results of our follow-up campaign of SN 2020faa. Given the high luminosity and peculiar slow light curve, it is purported to have a massive progenitor. We present the spectro-photometric dataset and investigate different options to explain the unusual observed properties that support this assumption. We computed the bolometric luminosity of the supernova and the evolution of its temperature, radius, and expansion velocity. We also fit the observed light curve with a multi-component model to infer information on the progenitor and the explosion mechanism. Reasonable parameters are inferred for SN 2020faa with a magnetar of energy Ep=1.5(+0.5,-0.2)x10^50 erg and spin-down time t(spin)=15+/-1 d, a shell mass M(shell)=2.4(+0.5,-0.4) Msun and kinetic energy Ekin(shell)=0.9(+0.5,-0.3)x 10^51 erg, and a core with M(core)=21.5(+1.4,-0.7) Msun and Ekin(core)=3.9(+0.1,-0.4)x10^51 erg. In addition, we need an extra source to power the luminosity of the second peak. We find that hidden interaction with either a CSM disc or delayed, choked jets is a viable mechanism for supplying the required energy to achieve this effect.

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arXiv2023

SN2017egm: A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves

When discovered, SN~2017egm was the closest (redshift $z=0.03$) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has since been extensively observed and studied. We report spectroscopic data showing strong emission at around He~I $λ$10,830 and four He~I absorption lines in the optical. Consequently, we classify SN~2017egm as a member of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We also present our late-time photometric observations. By combining them with archival data, we analyze high-cadence ultra-violet, optical, and near-infrared light curves spanning from early pre-peak ($\sim -20\,d$) to late phases ($\sim +300\,d$). We obtain its most complete bolometric light curve, in which multiple bumps are identified. None of the previously proposed models can satisfactorily explain all main light-curve features, while multiple interactions between the ejecta and circumstellar material (CSM) may explain the undulating features. The prominent infrared excess with a blackbody luminosity of $10^7$--$10^8\,L_{sun}$ detected in SN~2017egm could originate from the emission of either an echo of a pre-existing dust shell, or newly-formed dust, offering an additional piece of evidence supporting the ejecta-CSM interaction model. Moreover, our analysis of deep $Chandra$ observations yields the tightest-ever constraint on the X-ray emission of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio $\lesssim 10^{-3}$ at late phases ($\sim100-200\,d$), which could help explore its close environment and central engine.

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arXiv2022

The First Data Release of CNIa0.02 -- A Complete Nearby (Redshift <0.02) Sample of Type Ia Supernova Light Curves

The CNIa0.02 project aims to collect a complete, nearby sample of Type Ia supernovae (SNe Ia) light curves, and the SNe are volume-limited with host-galaxy redshifts z_host < 0.02. The main scientific goal is to infer the distributions of key properties (e.g., the luminosity function) of local SNe Ia in a complete and unbiased fashion in order to study SN explosion physics. We spectroscopically classify any SN candidate detected by the All-Sky Automated Survey for Supernovae (ASAS-SN) that reaches peak brightness < 16.5 mag. Since ASAS-SN scans the full sky and does not target specific galaxies, our target selection is effectively unbiased by host-galaxy properties. We perform multi-band photometric observations starting from the time of discovery. In the first data release (DR1), we present the optical light curves obtained for 247 SNe from our project (including 148 SNe in the complete sample), and we derive parameters such as the peak fluxes, dm15 and s_BV.

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