arXiv subjects

E. Baron

Publications and source records attributed to E. Baron.

At least 55 records · Page 3Linked to original sources

arXiv2022

SN 2021fxy: Mid-Ultraviolet Flux Suppression is a Common Feature of Type Ia Supernovae

We present ultraviolet (UV) to near-infrared (NIR) observations and analysis of the nearby Type Ia supernova SN 2021fxy. Our observations include UV photometry from Swift/UVOT, UV spectroscopy from HST/STIS, and high-cadence optical photometry with the Swope 1-m telescope capturing intra-night rises during the early light curve. Early $B-V$ colours show SN 2021fxy is the first "shallow-silicon" (SS) SN Ia to follow a red-to-blue evolution, compared to other SS objects which show blue colours from the earliest observations. Comparisons to other spectroscopically normal SNe Ia with HST UV spectra reveal SN 2021fxy is one of several SNe Ia with flux suppression in the mid-UV. These SNe also show blue-shifted mid-UV spectral features and strong high-velocity Ca II features. One possible origin of this mid-UV suppression is the increased effective opacity in the UV due to increased line blanketing from high velocity material, but differences in the explosion mechanism cannot be ruled out. Among SNe Ia with mid-UV suppression, SNe 2021fxy and 2017erp show substantial similarities in their optical properties despite belonging to different Branch subgroups, and UV flux differences of the same order as those found between SNe 2011fe and 2011by. Differential comparisons to multiple sets of synthetic SN Ia UV spectra reveal this UV flux difference likely originates from a luminosity difference between SNe 2021fxy and 2017erp, and not differing progenitor metallicities as suggested for SNe 2011by and 2011fe. These comparisons illustrate the complicated nature of UV spectral formation, and the need for more UV spectra to determine the physical source of SNe Ia UV diversity.

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arXiv2022

The Absolute Magnitudes of 1991T-like Supernovae

1991T-like supernovae are the luminous, slow-declining extreme of the Branch shallow-silicon (SS) subclass of Type Ia supernovae. They are distinguished by extremely weak Ca II H & K and Si II $\lambda6355$ and strong Fe III absorption features in their optical spectra at pre-maximum phases, and have long been suspected to be over-luminous compared to normal Type Ia supernovae. In this paper, the pseudo equivalent width of the Si II $λ$6355 absorption obtained at light curve phases from $\leq+10$ days is combined with the morphology of the $i$-band light curve to identify a sample of 1991T-like supernovae in the Carnegie Supernova Project-II. Hubble diagram residuals show that, at optical as well as near-infrared wavelengths, these events are over-luminous by $\sim$0.1-0.5 mag with respect to the less extreme Branch SS (1999aa-like) and Branch core-normal supernovae with similar $B$-band light curve decline rates.

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arXiv2022

Testing the Homogeneity of Type Ia Supernovae in the Near-Infrared for Accurate Distance Estimations

Type Ia Supernovae (SNe Ia) have been extensively used as standardisable candles in the optical for several decades. However, SNe Ia have shown to be more homogeneous in the near-infrared (NIR), where the effect of dust extinction is also attenuated. In this work, we explore the possibility of using a low number of NIR observations for accurate distance estimations, given the homogeneity at these wavelengths. We found that one epoch in $J$ and/or $H$ band, plus good $gr$-band coverage, gives an accurate estimation of peak magnitudes in $J$ ($J_{max}$) and $H$ ($H_{max}$) bands. The use of a single NIR epoch only introduces an additional scatter of $\sim0.05$ mag for epochs around the time of $B$-band peak magnitude ($T_{max}$). We also tested the effect of optical cadence and signal-to-noise ratio (S/N) in the estimation of $T_{max}$ and its uncertainty propagation to the NIR peak magnitudes. Both cadence and S/N have a similar contribution, where we constrained the introduced scatter of each to $<0.02$ mag in $J_{max}$ and $<0.01$ in $H_{max}$. However, these effects are expected to be negligible, provided the data quality is comparable to that obtained for observations of nearby SNe ($z\lesssim0.1$). The effect of S/N in the NIR was tested as well. For SNe Ia at $0.08<z\lesssim0.1$, NIR observations with better S/N than that found in the CSP sample is necessary to constrain the introduced scatter to a minimum ($\lesssim0.05$ mag). These results provide confidence for our FLOWS project that aims in using SNe Ia with public ZTF optical light curves and few NIR epochs to map out the peculiar velocity field of the local Universe. This will allow us to determine the distribution of dark matter in our own supercluster, Laniakea, and test the standard cosmological model by measuring the growth rate of structures, parameterised by $fD$, and the Hubble-Lemaître constant, $H_0$.

astro-ph.CO↗

arXiv2022

A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone can Explain Early-Excess Blue Flux in Some Type Ia Supernovae

We present early-time photometric and spectroscopic observations of the Type Ia Supernova (SN Ia) 2021aefx. The early time u-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early-excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca II H&K feature passing from the u to the B bands on the time scale of a few days. This effect could be dominant for all SNe Ia which have broad absorption features and early-time velocities over 25,000 km/s. It is likely to be one of the main causes of early-excess u-band flux in SNe Ia which have early-time high-velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the u-band. For objects which explode at lower velocities, and have a more structured shape in the early-excess emission, there must also be an additional parameter producing the early-time diversity. More early time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia.

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arXiv2022

SN 2019va: A Type IIP Supernova with Large Influence of Nickel-56 Decay on the Plateau-phase Light Curve

We present multi-band photometric and spectroscopic observations of the type II supernova, (SN) 2019va, which shows an unusually flat plateau-phase evolution in its V-band light curve. Its pseudo-bolometric light curve even shows a weak brightening towards the end of the plateau phase. These uncommon features are related to the influence of 56Ni decay on the light curve during the plateau phase, when the SN emission is usually dominated by cooling of the envelope. The inferred 56Ni mass of SN 2019va is 0.088+/-0.018 solar mass, which is significantly larger than most SNe II. To estimate the influence of 56Ni decay on the plateau-phase light curve, we calculate the ratio (dubbed as eta_Ni) between the integrated time-weighted energy from 56Ni decay and that from envelope cooling within the plateau phase, obtaining a value of 0.8 for SN 2019va, which is the second largest value among SNe II that have been measured. After removing the influence of 56Ni decay on the plateau-phase light curve, we found that the progenitor/explosion parameters derived for SN 2019va are more reasonable. In addition, SN 2019va is found to have weaker metal lines in its spectra compared to other SNe IIP at similar epochs, implying a low-metallicity progenitor, which is consistent with the metal-poor environment inferred from the host-galaxy spectrum. We further discuss the possible reasons that might lead to SN 2019va-like events.

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arXiv2022

A Tale of Two Type Ia Supernovae: The fast-declining siblings SNe 2015bo and 1997cn

We present optical and near-infrared photometric and spectroscopic observations of the fast-declining Type Ia Supernova (SN) 2015bo. SN 2015bo is under-luminous (M$_B$ = -17.67 $\pm$ 0.15 mag) and has a fast-evolving light curve ($Δ\mathrm{m}_{15}\mathrm{(B)}$ = 1.91 $\pm$ 0.01 mag and $s_{BV}$ = 0.48 $\pm$ 0.01). It has a unique morphology in the $V-r$ color curve, where it is bluer than all other SNe in the comparison sample. A $^{56}$Ni mass of 0.17 $\pm$ 0.03 $M_{\odot}$ was derived from the peak bolometric luminosity, which is consistent with its location on the luminosity-width relation. Spectroscopically, SN 2015bo is a Cool SN in the Branch classification scheme. The velocity evolution measured from spectral features is consistent with 1991bg-like SNe. SN 2015bo has a SN twin (similar spectra) and sibling (same host galaxy), SN 1997cn. Distance moduli of $μ$ = 34.33 $\pm$ 0.01 (stat) $\pm$0.11 (sys) mag and $μ$ = 34.34 $\pm$ 0.04 (stat) $\pm$ 0.12 (sys) mag were derived for SN 2015bo and SN 1997cn, respectively. These distances are consistent at the 0.06-$σ$ level with each other, and are also consistent with distances derived using surface-brightness fluctuations and redshift-corrected cosmology. This suggests that fast-declining SNe could be accurate distance indicators which should not be excluded from future cosmological analyses.

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arXiv2021

Carnegie Supernova Project: kinky $i$-band light-curves of Type Ia supernovae

We present detailed investigation of a specific $i$-band light-curve feature in Type Ia supernovae (SNe Ia) using the rapid cadence and high signal-to-noise ratio light-curves obtained by the Carnegie Supernova Project. The feature is present in most SNe Ia and emerges a few days after the $i$-band maximum. It is an abrupt change in curvature in the light-curve over a few days and appears as a flattening in mild cases and a strong downward concave shape, or a "kink", in the most extreme cases. We computed the second derivatives of Gaussian Process interpolations to study 54 rapid-cadence light-curves. From the second derivatives we measure: 1) the timing of the feature in days relative to $i$-band maximum; tdm$_{2}$($i$) and 2) the strength and direction of the concavity in mag d$^{-2}$ ; dm$_{2}$($i$). 76$\%$ of the SNe Ia show a negative dm$_{2}$($i$), representing a downward concavity - either a mild flattening or a strong "kink". The tdm$_{2}$($i$) parameter is shown to correlate with the color-stretch parameter s$_{\mathrm{BV}}$, a SN Ia primary parameter. The dm$_{2}$($i$) parameter shows no correlation with s$_{\mathrm{BV}}$ and therefore provides independent information. It is also largely independent of the spectroscopic and environmental properties. Dividing the sample based on the strength of the light-curve feature as measured by dm$_{2}$($i$), SNe Ia with strong features have a Hubble diagram dispersion of 0.107 mag, 0.075 mag smaller than the group with weak features. Although larger samples should be obtained to test this result, it potentially offers a new method for improving SN Ia distance determinations without shifting to more costly near-infrared or spectroscopic observations.

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arXiv2021

Carnegie Supernova Project-II: Near-infrared Spectroscopy of Stripped-Envelope Core-Collapse Supernovae

We present 75 near-infrared (NIR; 0.8$-$2.5 $μ$m) spectra of 34 stripped-envelope core-collapse supernovae (SESNe) obtained by the Carnegie Supernova Project-II (CSP-II), encompassing optical spectroscopic Types IIb, Ib, Ic, and Ic-BL. The spectra range in phase from pre-maximum to 80 days past maximum. This unique data set constitutes the largest NIR spectroscopic sample of SESNe to date. NIR spectroscopy provides observables with additional information that is not available in the optical. Specifically, the NIR contains the resonance lines of He I and allows a more detailed look at whether Type Ic supernovae are completely stripped of their outer He layer. The NIR spectra of SESNe have broad similarities, but closer examination through statistical means reveals a strong dichotomy between NIR "He-rich" and "He-poor" SNe. These NIR subgroups correspond almost perfectly to the optical IIb/Ib and Ic/Ic-BL types, respectively. The largest difference between the two groups is observed in the 2 $μ$m region, near the He I $λ$2.0581 $μ$m line. The division between the two groups is not an arbitrary one along a continuous sequence. Early spectra of He-rich SESNe show much stronger He I $λ$2.0581 $μ$m absorption compared to the He-poor group, but with a wide range of profile shapes. The same line also provides evidence for trace amounts of He in half of our SNe in the He-poor group.

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arXiv2021

SN 2018hfm : A Low-Energy Type II Supernova with Prominent Signatures of Circumstellar Interaction and Dust Formation

We present multiband optical photometric and spectroscopic observations of an unusual Type II supernova, SN 2018hfm, which exploded in the nearby (d = 34.67 Mpc) dwarf galaxy PGC 1297331 with a very low star-formation rate (0.0270 M yr-1) and a subsolar metallicity environment(~ 0.5 Z). The V-band light curve of SN 2018hfm reaches a peak with value of -18.69+/-0.64 mag, followed by a fast decline(4.42+/-0.13 mag (100d)-1). After about 50 days, it is found to experience a large flux drop (~3.0 mag in V), and then enters into an unusually faint tail, which indicates a relatively small amount of 56Ni synthesized during the explosion. From the bolometric light curve, SN 2018hfm is estimated to have low ejecta mass (~1.3M) and low explosion energy(~10 50 erg) compared with typical SNe II. The photospheric spectra of SN 2018hfm are similar to those of other SNe II, with P Cygni profiles of the Balmer series and metal lines, while at late phases the spectra are characterised by box-like profiles of HU emission, suggesting significant interaction between the SN ejecta and circumstellar matter. These box-like emission features are found to show increasing asymmetry with time, with the red-side component becoming gradually weaker, indicating that dust is continuously formed in the ejecta. Based on the dust-estimation tool damocles, we find that the dust increases from ~10 -6M to 10 -4 - 10 -3 M between +66.7 d and +389.4 d after explosion.

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arXiv2021

ASASSN-15hy: an under-luminous, red 03fg-like type Ia supernova

We present photometric and spectroscopic observations of the 03fg-like type Ia supernova (SN Ia) ASASSN-15hy from the ultraviolet (UV) to the near-infrared (NIR). ASASSN-15hy shares many of the hallmark characteristics of 03fg-like SNe Ia, previously referred to as "super-Chandrasekhar" SNe Ia. It is bright in the UV and NIR, lacks a clear i-band secondary maximum, shows a strong and persistent C II feature, and has a low Si II $λ$6355 velocity. However, some of its properties are also extreme among the subgroup. ASASSN-15hy is under-luminous (M$_{B,peak}=-19.14^{+0.11}_{-0.16}$ mag), red ($(B-V)_{Bmax}=0.18^{+0.01}_{-0.03}$ mag), yet slowly declining ($Δ{m_{15}}(B)=0.72 \pm 0.04$ mag). It has the most delayed onset of the i-band maximum of any 03fg-like SN. ASASSN-15hy lacks the prominent H-band break emission feature that is typically present during the first month past maximum in normal SNe Ia. Such events may be a potential problem for high-redshift SN Ia cosmology. ASASSN-15hy may be explained in the context of an explosion of a degenerate core inside a non-degenerate envelope. The explosion impacting the non-degenerate envelope with a large mass provides additional luminosity and low ejecta velocities. An initial deflagration burning phase is critical in reproducing the low $^{56}$Ni mass and luminosity, while the large core mass is essential in providing the large diffusion time scales required to produce the broad light curves. The model consists of a rapidly rotating 1.47 $M_{\odot}$ degenerate core and a 0.8 $M_{\odot}$ non-degenerate envelope. This "deflagration core-degenerate" scenario may result from the merger between a white dwarf and the degenerate core of an asymptotic giant branch star.

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arXiv2021

Measuring an off-Center Detonation through Infrared Line Profiles: The peculiar Type Ia Supernova SN~2020qxp/ASASSN-20jq

We present and analyze a near infrared(NIR) spectrum of the under-luminous Type Ia supernova SN~2020qxp/ASASSN-20jq obtained with NIRES at the Keck Observatory 191 days after B-band maximum. The spectrum is dominated by a number of broad emission features including the [FeII] at 1.644mu which is highly asymmetric with a tilted top and a peak red-shifted by ~2,000km/s. In comparison with 2-D non-LTE synthetic spectra computed from 3-D simulations of off-center delayed-detonation Chandrasekhar-mass white-dwarf(WD) models, we find good agreement between the observed lines and the synthetic profiles, and are able to unravel the structure of the progenitor's envelope. We find that the size and tilt of the [Fe II] 1.644mu-profile (in velocity space) is an effective way to determine the location of an off-center delayed-detonation transition (DDT) and the viewing angle, and it requires a WD with a high central density of ~4E9$g/cm^3$. We also tentatively identify a stable Ni feature around 1.9mu characterized by a `pot-belly' profile that is slightly offset with respect to the kinematic center. In the case of SN~2020qxp/ASASSN-20jq, we estimate that the location of the DDT is ~0.3M(WD) off-center, which gives rise to an asymmetric distribution of the underlying ejecta. We also demonstrate that low-luminosity and high-density WD SNIa progenitors exhibit a very strong overlap of Ca and 56Ni in physical space. This results in the formation of a prevalent [Ca II] 0.73mu emission feature, which is sensitive to asymmetry effects. Our findings are discussed within the context of alternative scenarios, including off-center C/O detonations in He-triggered sub-M(Ch)-WDs and the direct collision of two WDs. Snapshot programs with Gemini/Keck/VLT/ELT class instruments and our spectropolarimetry program are complementary to mid-IR spectra by JWST.

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arXiv2021

Carnegie Supernova Project: The First Homogeneous Sample of "Super-Chandrasekhar Mass"/2003fg-like Type Ia Supernova

We present a multi-wavelength photometric and spectroscopic analysis of thirteen "Super-Chandrasekhar Mass"/2003fg-like type Ia Supernova (SNe~Ia). Nine of these objects were observed by the Carnegie Supernova Project. 2003fg-like have slowly declining light curves ($Δm_{15}$(B) $<$1.3 mag), and peak absolute $B$-band magnitudes between $-19<M_{B}<-21$~mag. Many 2003fg-like are located in the same part of the luminosity width relation as normal SNe~Ia. In the optical $B$ and $V$ bands, 2003fg-like look like normal SNe~Ia, but at redder wavelengths they diverge. Unlike other luminous SNe~Ia, 2003fg-like generally have only one $i$-band maximum which peaks after the epoch of $B$-band maximum, while their NIR light curve rise times can be $\gtrsim$40 days longer than those of normal SNe~Ia. They are also at least one magnitude brighter in the NIR bands than normal SNe~Ia, peaking above $M_H < -19$~mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark energy experiments. Spectroscopically, 2003fg-like exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000--12000~km/s) in SiII $λ$6355 velocities at maximum light with no rapid early velocity decline, and no clear $H$-band break at +10~d, e. We find that SNe with a larger pseudo equivalent width of CII at maximum light have lower SiII $λ$6355 velocities and slower declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like. The explosion of a C-O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core degenerate scenario.

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arXiv2021

SN 2021csp -- the explosion of a stripped envelope star within a H and He-poor circumstellar medium

We present observations of SN 2021csp, a unique supernova (SN) which displays evidence for interaction with H- and He- poor circumstellar material (CSM) at early times. Using high-cadence spectroscopy taken over the first week after explosion, we show that the spectra of SN 2021csp are dominated by C III lines with a velocity of 1800 km s$^{-1}$. We associate this emission with CSM lost by the progenitor prior to explosion. Subsequently, the SN displays narrow He lines before metamorphosing into a broad-lined Type Ic SN. We model the bolometric light curve of SN 2021csp, and show that it is consistent with the energetic ($4\times10^{51}$ erg) explosion of a stripped star, producing 0.4 M$_\odot$ of 56Ni within a $\sim$1 M$_\odot$ shell of CSM extending out to 400 R$_\odot$.

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arXiv2021

A 3D radiative transfer framework: XII. Many-core, vector and GPU methods

3D detailed radiative transfer is computationally taxing, since the solution of the radiative transfer equation involves traversing the six dimensional phase space of the 3D domain. With modern supercomputers the hardware available for wallclock speedup is rapidly changing, mostly in response to requirements to minimize the cost of electrical power. Given the variety of modern computing architectures, we aim to develop and adapt algorithms for different computing architectures to improve performance on a wide variety of platforms. We implemented the main time consuming kernels for solving 3D radiative transfer problems for vastly different computing architectures using MPI, OpenMP, OpenACC and vector algorithms. Adapted algorithms lead to massively improved speed for all architectures, making extremely large model calculations easily feasible. These calculations would have previously been considered impossible or prohibitively expensive. Efficient use of modern computing devices is entirely feasible, but unfortunately requires the implementation of specialized algorithms for them.

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arXiv2020

The Carnegie Supernova Project II. Observations of the intermediate luminosity red transient SNhunt120

We present multi-wavelength observations of two gap transients followed by the Carnegie Supernova Project-II and supplemented with data obtained by a number of different programs. Here in the first of two papers, we focus on the intermediate luminosity red transient (ILRT) designated SNhunt120, while in a companion paper we examine the luminous red novae AT 2014ej. Our data set for SNhunt120 consists of an early optical discovery, estimated to be within 3 days after outburst, the subsequent optical and near-infrared broadband followup extending over a $\sim$2 month period, two visual- and two near-infrared wavelength spectra, and Spitzer Space Telescope observations extending from early ($+$28 d) to late ($+$1155 d) phases. SNhunt120 resembles other ILRTs such as NGC 300-2008-OT and SN 2008S, and like these other ILRTs, SNhunt120 exhibits prevalent mid-infrared emission at both early and late phases. From the comparison of SNhunt120 and other ILRTs to electron-capture supernova simulations, we find that the current models underestimate the explosion kinetic energy and thereby produce synthetic light curves that over-estimate the luminosity. Finally, examination of pre-outburst Hubble Space Telescope images yields no progenitor detection.

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arXiv2020

The Carnegie Supernova Project II. Observations of the luminous red nova AT 2014ej

We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double hump light curve and spectral properties akin to the LRN SN 2017jfs. A medium-dispersion, visual-wavelength spectrum of AT 2014ej taken the Magellan Clay telescope, exhibits a P Cygni H$α$ feature characterized by a blue velocity at zero intensity of $\approx 110$ km s$^{-1}$ and a P Cygni minimum velocity of $\approx70$ km s$^{-1}$, and which we attribute to emission from a circumstellar wind. Inspection of pre-outbust Hubble Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies among the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared (UVOIR) light curves of well-observed LRNe to common-envelope evolution models from the literature, indicates the models under predict the luminosity of the comparison sample at all phases and also produce inconsistent time-scales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space explored and therefore may consider more massive systems and a wider range of dynamical timescales.

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arXiv2020

Carnegie Supernova Project: Classification of Type Ia Supernovae

We use the spectroscopy and homogeneous photometry of 97 Type Ia supernovae obtained by the \emph{Carnegie Supernova Project} as well as a subset of 36 Type Ia supernovae presented by Zheng et al. (2018) to examine maximum-light correlations in a four-dimensional (4-D) parameter space: $B$-band absolute magnitude, $M_B$, \ion{Si}{2}~$\lambda6355$ velocity, \vsi, and \ion{Si}{2} pseudo-equivalent widths pEW(\ion{Si}{2}~$\lambda6355$) and pEW(\ion{Si}{2}~$\lambda5972$). It is shown using Gaussian mixture models (GMMs) that the original four groups in the Branch diagram are well-defined and robust in this parameterization. We find three continuous groups that describe the behavior of our sample in [$M_B$, \vsi] space. Extending the GMM into the full 4-D space yields a grouping system that only slightly alters group definitions in the [$M_B$, \vsi] projection, showing that most of the clustering information in [$M_B$, \vsi] is already contained in the 2-D GMM groupings. However, the full 4-D space does divide group membership for faster objects between core-normal and broad-line objects in the Branch diagram. A significant correlation between $M_B$ and pEW(\ion{Si}{2}~$\lambda5972$) is found, which implies that Branch group membership can be well-constrained by spectroscopic quantities alone. In general, we find that higher-dimensional GMMs reduce the uncertainty of group membership for objects between the originally defined Branch groups. We also find that the broad-line Branch group becomes nearly distinct with the inclusion of \vsi, indicating that this subclass of SNe Ia may be somehow different from the other groups.

astro-ph.HE↗

arXiv2020

SN 2018hti: a nearby superluminous supernova discovered in a metal-poor galaxy

SN 2018hti is a Type I superluminous supernova (SLSN~I) with an absolute $g$-band magnitude of $-22.2$ at maximum brightness, discovered in a metal-poor galaxy at a redshift of 0.0612. We present extensive photometric and spectroscopic observations of this supernova, covering the phases from $\sim -35$ days to more than +340 days from the $r$-band maximum. Combining our $BVgri$-band photometry with {\it Swift} UVOT optical/ultraviolet photometry, we calculated the peak luminosity as $\sim 3.5\times10^{44}$ erg s$^{-1}$. Modeling the observed light curve reveals that the luminosity evolution of SN 2018hti can be produced by an ejecta mass of 5.8 $M_\odot$ and a magnetar with a magnetic field of $B=1.8\times10^{13}$~G having an initial spin period of $P_0=1.8$ ms. Based on such a magnetar-powered scenario and a larger sample, a correlation between the spin of the magnetar and the kinetic energy of the ejecta can be inferred for most SLSNe~I, suggesting a self-consistent scenario. Like for other SLSNe~I, the host galaxy of SN 2018hti is found to be relatively faint ($M_{g} = -17.75$ mag) and of low metallicity ($Z=0.3~Z_\odot$), with a star-formation rate of 0.3 $M_\odot$ yr$^{-1}$. According to simulation results of single-star evolution, SN 2018hti could originate from a massive, metal-poor star with a zero-age main sequence (ZAMS) mass of 25--40 $M_\odot$, or from a less massive rotating star with $M_\mathrm{ZAMS} \approx 16$--25 $M_\odot$. For the case of a binary system, its progenitor could also be a star with $M_\mathrm{ZAMS} \gtrsim 25$ $M_\odot$.

astro-ph.HE↗