Searcharxiv⌕ Search

arXiv subjects

K. Azalee Bostroem

Publications and source records attributed to K. Azalee Bostroem.

At least 19 recordsLinked to original sources
arXiv2026

Aarmed with Data: Bumps, Outflows, and Disk-like Emission in TDE 2025aarm

The origin of the optical emission in tidal disruption events (TDEs) remains one of the major outstanding questions in the field, in part due to the limited number of nearby events with high-cadence monitoring to track their evolving photometric and spectroscopic properties. We present multi-wavelength observations of the nearby ($z=0.01368$) TDE\,2025aarm, including near-daily spectroscopic coverage prior to the optical peak. Its proximity makes it one of the brightest TDEs discovered, reaching a peak magnitude of $m_r\sim15.5$ ($M_r\sim-18$). The light curve deviates from a smooth evolution, exhibiting multiple rebrightening episodes visible in both the individual filter light curves and the bolometric luminosity. Blackbody modelling reveals that these rebrightenings are associated with an increase in temperature of $> 5,000-10,000$\,K, while the inferred photospheric radius remains approximately constant. Simultaneously, the H$\alpha$ line not only increases in blueshift but also broadens, suggesting a link between the continuum rebrightenings to changes in the kinematics of the line-forming gas. We identify a persistent absorption component at $\sim-3900$\,km\,s$^{-1}$ in multiple Balmer lines, providing further evidence for outflowing material. The H$\alpha$ profile also exhibits excess flux compared to a Gaussian on both sides of the line, inconsistent with simple scattering-dominated outflow models. Disk-profile modelling provides evidence for the emergence of a disk-like component least $\sim20$ days after peak, with substantial changes in the disk properties between $\sim50$ and 60 days. These observations highlight the complexity of TDE emission processes and demonstrate how dense multi-wavelength monitoring can disentangle the roles of accretion, reprocessing, and outflows in shaping TDE emission.

astro-ph.HE↗
arXiv2026

SN 2019cqc: A Hydrogen-rich Superluminous Supernova Showing Electron-Scattering Signatures

Hydrogen-rich superluminous supernovae without narrow emission lines (SLSNe-II) are rare transients whose powering mechanisms remain debated, particularly the role of circumstellar medium (CSM) interaction. We present photometric and spectroscopic observations of SN 2019cqc to investigate its power source and progenitor mass loss. We model the lightcurve using MOSFiT with the csm and csmni models to constrain the explosion and CSM parameters. SN 2019cqc peaked at $M_g = -20.21 \pm 0.07$ and emitted $\sim 1.7 \times 10^{50}\,\mathrm{erg}$ of energy in the form of radiation. Photometric and spectroscopic modeling indicates that CSM interaction dominates in both scenarios, with best-fit CSM and ejecta masses of $\sim 4.5~ M_\odot$ and $\sim 32~ M_\odot$, respectively. The inferred CSM properties imply an extreme eruptive mass loss at a rate of $\sim 0.2--0.3 ~M_\odot\,\mathrm{yr^{-1}}$ in the years preceding the core collapse, consistent with a variable progenitor of luminous blue variable progenitor. We observe a persistent blueshifted asymmetry in the H$\alpha$ emission line. At early times ($\lesssim +110$~d), this is attributed to electron scattering with bulk Velocity of ejecta, while the profile at late epochs ($\gtrsim +402$~d onward) suggests the subsequent formation of dust in the ejecta. Additionally, we identify a distinct, short-lived feature at $\sim$ 4600 {\AA} , likely a blend of ionized C III/N III lines powered by the interaction of the SN-shock with the extended atmosphere.

astro-ph.HE↗
arXiv2026

A JWST/MIRI Study of Dust in a Sample of Normal Type IIP Core Collapse Supernovae

Core collapse supernovae (CCSNe) are invoked as major dust producers in the early Universe, yet the amount of dust they form, the timescale over which it grows, and the physical conditions that regulate the yield remain uncertain. We present a detailed JWST/MIRI mid-infrared (MIR) imaging census of 11 nearby Type IIP CCSNe spanning $\sim$1-7 yr after explosion, investigating dust emission across the different phases of their evolution. The spectral energy distributions show a coherent evolution from hot ($\sim$1500 K), 5-8 $\mu$m emission at $\sim$400 d to prominent 10 and 18 $\mu$m emission features at later epochs ($\sim$600-2500 d). The cool dust temperatures range from $\sim120$ to $250$ K and dust masses from $\sim10^{-4}$ to $10^{-2} M_{\odot}$. The current sample shows no statistically significant correlation between measured dust mass and peak luminosity, plateau duration, or explosion energy. SNe with early high ionization features, indicative of confined CSM, are often among the dust-rich objects in the sample. The measured 1-7 yr dust yields are insufficient to account for dust in typical $z > 6$ galaxies, but support a role for CCSNe as producers of seed dust for subsequent grain growth.

astro-ph.HE↗
arXiv2026

No Evidence for Nearby Circumstellar Material in the Type Ia Supernova 2025rbs

We present a high-resolution spectral time series of the Type Ia supernova (SN) 2025rbs discovered in the nearby galaxy NGC 7331. The Automated Planet Finder (APF) at Lick Observatory and the MAROON-X/IGRINS-2 at Gemini North were used to obtain echelle spectra between -5 and 15 days with respect to the epoch of maximum light. Several unsaturated NaID absorption components along the line of sight are identified, but there is no evidence of time variance in any of them. We measure the equivalent width of the observed diffuse interstellar band around 5780 A and constrain the extinction along the line of sight to SN 2025rbs as $A_V = 0.64\,\pm\,0.32$ mag, corresponding to a moderate reddening of $E(B-V) = 0.21\,\pm\,0.10$ mag (assuming $R_\mathrm{V}$ = 3.1). The observed Ca II H & K interstellar absorption roughly traces NaID in velocity space, suggesting a common origin. Quantitative comparisons between the column densities of Na and Ca gas in these host clouds ($N_{NaID}$ / $N_{Ca II}$ of order unity) argue against their origin in the Galactic halo gas and instead support absorption due to the interstellar gas of NGC 7331. Time invariance of all the observed absorption features suggests a lack of nearby circumstellar material ($\lesssim$ 10$^{16}$ cm) around the progenitor system of SN 2025rbs. This supports a progenitor scenario for SN 2025rbs with minimal ambient circumstellar gas, consistent with a double-degenerate CO white dwarf binary system.

astro-ph.HE↗
arXiv2026

JWST Spectroscopy of Type Ia Supernova 2025rbs from Maximum Light to the Nebular Phase

We present JWST observations of the Type Ia supernova (SN Ia) 2025rbs ($D=$14.5 Mpc) at +1, +23, and +84 days after B-band maximum, spanning peak light through a wavelength-dependent transition toward the nebular phase. Combined with ground-based optical and near-infrared (NIR) data, our panchromatic spectra (0.4-14 $\mu$m) include the first maximum-light mid-infrared (MIR) spectrum and the earliest MIR spectroscopic sequence of an SN Ia to date. At peak light, the MIR spectrum exhibits a continuum with permitted and forbidden features, including Si II, Ni II, and early-emerging [Ni III-IV] and [Ar II-III]. By +23 days the MIR is dominated by forbidden lines with a weak continuum, and by +84 days it is fully nebular, whereas the optical/NIR spectra remain transitional. The nebular spectrum reveals strongly stratified ejecta, with stable Ni concentrated at the lowest velocities, radioactive Co at intermediate velocities but absent within ~2000 km s$^{-1}$, and Ar occupying an outer shell. We detect small-scale substructure in [Ca IV] 3.21 $\mu$m with fractional amplitudes of a few percent and a characteristic velocity scale of ~800 km s$^{-1}$, which may reflect compositional structure, ionization variations, or both. Radiative-transfer calculations substantially underpredict these MIR Mg II features despite approximately reproducing the NIR Mg II 1.0927 $\mu$m line, suggesting that the relative strengths of these transitions are sensitive to the treatment of Mg ionization and excitation. These observations demonstrate that MIR spectroscopy beginning near maximum light simultaneously probes the emerging inner ejecta and rapidly fading outer burning products, providing new constraints for explosion and radiative-transfer models.

astro-ph.HE↗
arXiv2026

SN 2022xus: bridging the gap between Type IIP and IIL supernovae

We present optical photometric and spectroscopic observations of the Type~II supernova SN~2022xus. The SN reached its peak {\em V} band magnitude of $-16.32$ mag within $\sim$7 days of explosion, followed by a plateau phase lasting $\sim$94 days with a declination rate of $\sim$1.2 mag (100 day)$^{-1}$. Early time spectra exhibit broad features that could be caused by the blending of several high-ionisation lines, likely arising from a relatively weak interaction between the SN ejecta and the surrounding circumstellar medium (CSM). Compared to typical Type~IIP SNe, SN~2022xus exhibits a smaller H$\alpha$ absorption-to-emission ratio ($a/e$), indicating a relatively small hydrogen envelope mass at the time of explosion. From nebular-phase spectroscopy and bolometric light curve modelling, the progenitor mass is estimated to be in the range of 12 -- 15 M$_\odot$. The multi-band light curve modelling using \texttt{REDBACK} infers a similar progenitor mass, a low mass-loss rate, and a confined CSM. Although several photometric and spectroscopic characteristics place the SN within the Type~IIL population, it displays mixed properties of both Type~IIP and Type~IIL SNe and cannot be cleanly classified into either subclass. We therefore identify SN~2022xus as a transitional event between Type~IIP and Type~IIL SNe, providing further evidence for a continuum between these two classes.

astro-ph.HE↗
arXiv2026

Ultraviolet to Infrared Spectroscopy of the Type Ibn SN 2023tsz Suggests a Lower-mass Progenitor

Type Ibn supernovae are stripped-envelope explosions whose spectra indicate interaction with dense, helium-rich and hydrogen-poor circumstellar material (CSM), making them important probes of late-stage mass loss and progenitor stripping. We present extensive ultraviolet-to-near-infrared spectrophotometry of the Type Ibn SN 2023tsz, including two epochs of HST/STIS ultraviolet (UV) spectroscopy and ground-based optical and near-infrared follow-up observations. The spectra are dominated by intermediate-width emission lines at all phases after maximum light, suggesting that much of the luminosity originates in a cold dense shell (CDS) formed by interaction between the ejecta and CSM. We compare the observations to one-dimensional non-local-thermodynamic-equilibrium radiative-transfer models of a helium-star explosion with a mass of $4 M_{\odot}$ at the onset of helium burning. The models reproduce the strong optical and near-infrared He I lines and require an added X-ray irradiation field to match the highly ionized UV features. The spectra are best reproduced by models with an X-ray irradiation power of $L_X \approx 10^8 L_{\odot}$, with the preferred models favoring CDS radii of order $(1.5$--$2) \times 10^{15}$ cm, velocities of $\sim 5 \times 10^7$ cm s$^{-1}$, and interaction powers of a few times $10^{42}$ erg s$^{-1}$. In the optical, the preferred models shift from higher interaction power and smaller radii at early times to lower power and larger radii at later times. These results add to the growing evidence that at least some SNe Ibn arise from lower-mass helium stars whose final evolution is shaped by binary interaction.

astro-ph.HE↗
arXiv2026

Evidence for Asymmetric Ejecta and Circumstellar Material in SN 2023ixf Inferred from Extensive Nebular-phase Observations

We present extensive optical and near-infrared (NIR) observations of the nearby Type II supernova (SN II) 2023ixf in the nebular phase from +89 days to +749 days after explosion, supplemented with NIR and mid-infrared (MIR) spectroscopy from the James Webb Space Telescope. The H$\alpha$ emission profile shows complex evolution, with the emergence of high-velocity components consistent with the outer ejecta interacting with extended, low-density circumstellar material (CSM). We find that the H$\alpha$ profile at an intermediate epoch (around +375 d) can be reconstructed by scaling an earlier decay-powered component and a later-phase shock-powered component, which revealed an additional intermediate-width component. This is consistent with the ejecta crashing into the initially aspherical dense CSM that has been swept-up by the forward shock. In the NIR, we find double-peaked emission from Mg I $1.504\ {\rm \mu m}$, Na I $2.206\ {\rm \mu m}$, and [Ni I] $3.12\ {\rm \mu m}$ between +200 d and +374 d, consistent with an asymmetric distribution of Ni-rich material that heats the ejecta inhomogeneously. We posit a disk-like CSM geometry and an ejecta geometry in which at least two large Ni-rich plumes lead to the observed line-profile diversity.

astro-ph.HE↗
arXiv2026

SN 2020bij and a Possible Slow-Rise High-Velocity Subclass of Type IIP Supernovae

Mapping how the explosion properties of Type II supernovae (SNe II) relate to the properties of their progenitors can provide strong constraints for understanding the final evolutionary stages of massive stars. Type IIP SNe, linked to the explosions of single red super-giant (RSG) stars, have recently been found to require some form of interaction with circumstellar material (CSM) to reproduce the rapid rise to the plateau often seen in their light curves. In this work, we present observations and analysis of the Type IIP SN 2020bij, characterized by a slow rise to its plateau as well as high expansion velocities. We identify four other SNe IIP from the literature (ASASSN-14kg, SN 2018fif, SN 2021yja and SN 2023axu) with similarly slowly rising light curves and find that they also show high expansion velocities. Using both analytical and numerical models, all five events can be explained with weak to no CSM interaction. We therefore propose that these events constitute a new subclass of Type IIP SNe which could be associated with relatively confined CSM. Early and dense photometric coverage of future SNe IIP together with early spectroscopic observations will further map this subclass and its physical properties. Understanding such rare events could be key to constraining the diversity of late-stage mass-loss in RSGs.

astro-ph.HE↗
arXiv2026

JWST Observations of Calcium-Strong Transients: I. Complex Nebular He Emission in SN 2024uj

We present the first JWST observations of a Calcium-Strong Transient (CaST), SN 2024uj, a rare class of supernovae (SNe) with observable properties that are consistent with both thermonuclear explosions of white dwarfs (WDs) and the core collapse of massive stars. SN 2024uj is offset by $\sim6.6$ kpc from its host and exhibits a double-peaked light curve consistent with shock cooling of nearby circumstellar material. At early times, its optical spectra resemble those of normal SNe Ib, but strong [Ca II] $\lambda\lambda$7291, 7324 emission emerges between $+$2 and $+$17 days after maximum light. Radiative-transfer models of a massive stripped He star cannot reproduce this early forbidden Ca emission, even with artificially enhanced surface Ca, whereas it arises naturally in thermonuclear scenarios. The $+$150 d JWST/NIRSpec spectrum reveals highly asymmetric, multicomponent He I at both 1.083 and 2.058 $\mu$m. The He extends to $\gtrsim+$5000 km/s, with a strong, narrow peak at $+$1500 km/s, indicating that He is distributed throughout the ejecta with a concentration offset from center. This He distribution overlaps central [Ca II] and [O I], implying a degree of mixing difficult to produce in a massive star explosion. The He peak might further trace interaction with a shocked, ejected companion in a thermonuclear system. The NIRSpec spectrum also shows molecular CO emission and a rising continuum that, together with a 10 $\mu$m photometric detection, indicates dust emission extending into the mid-infrared. Given the remote environment, early forbidden Ca, mixed He/Ca/O ejecta, and possible companion signature, we favor a thermonuclear origin for SN 2024uj involving at least one low-mass, partially He-rich WD.

astro-ph.HE↗
arXiv2026

SN 2023rve: A Type II Supernova with No Nebular Oxygen

We report on multiband photometric and spectroscopic observations of SN 2023rve, a nearby Type II supernova (SN II) discovered in galaxy NGC 1097 (D=$15.4 \pm 3.2$ Mpc). Nearby SNe II provide constraints on late-stage evolution and progenitor mass loss, particularly the role of circumstellar material (CSM) in shaping SN II observables. SN 2023rve peaks with an absolute V-band magnitude of -17.1 and declines at a rate of $0.90 \pm 0.02$ mag/50 days during the plateau. The bolometric light curve implies a $^{56}$Ni mass of 0.0064 $M_\odot$. Using hydrodynamic light-curve modeling, we infer an intermediate-mass progenitor (~14-18 $M_\odot$), a low explosion energy of 0.27 $\times 10^{51}$ ergs, and a dense CSM component with radial extent of 2900 $R_\odot$ and density of $10^{18}$g cm$^{-1}$. This supports growing evidence that enhanced pre-SN mass loss influences the diversity of SNe II. The nebular spectra of SN 2023rve show narrow He I lines and an absence of [O I] lines unprecedented among Type II SNe. Comparison with other SNe II shows that only two other known objects, both with higher velocities, lack oxygen signatures at similar epochs, <10% of the sample. The lack of oxygen emission combined with low explosion energy, a long plateau, and a small synthesized nickel mass may be consistent with partial fallback of material onto the compact remnant. We also discuss alternative explanations for the suppressed oxygen emission, including dust formation, oxygen-calcium mixing, and ongoing CSM interaction.

astro-ph.HE↗
arXiv2026

JWST observations of SN 2024abup: First Detection of CO in a broad-lined Type Ic Supernova and Constraints on r-process Nucleosynthesis

SN 2024abup is a nearby broad-lined Type Ic supernova (SN Ic-bl) in NGC 0681 at a distance of 23.3 \pm 1.6 Mpc. As energetic explosions of massive stars, SNe Ic-bl are considered a plausible site for rapid-neutron capture nucleosynthesis (r-process) and chemical enrichment from short-lived progenitors. They may also contribute to dust production in the early Universe. We present JWST near- to mid-infrared (NIR+MIR) observations (1-14 micron) of SN Ic-bl 2024abup at +41 days after the V band maximum (+54 days after explosion), the first-ever JWST+MIR observation of a SN Ic-bl along with radio and optical data. Using the spectral synthesis code SUMO, we identify the observed broad IR line features in SN 2024abup and find significant contributions from C, O, Mg, and carbon monoxide (CO) -- the earliest detection of molecules in a core-collapse SN so far. The spectrum shows continuum emission at wavelengths greater than 1.5 micron, which could be explained by dust -- preexisting, newly formed, or a combination-heated by the SN. We do not find compelling evidence for infrared signatures of r-process elements, though our search is hampered by the presence of many broad and blended features from the non-r-process elements. These new observations indicate that SNe Ic-bl could be a contributor to early-universe dust production, and suggest that if r-process elements are produced, revealing their presence from spectra requires very high-quality data and models to disentangle blends.

astro-ph.HE↗
arXiv2026

First Results from the LSST Shadow Survey: The Restless Luminous Blue Variable AT2017des in the Virgo-Cluster Galaxy, NGC4532

The Legacy Survey of Space and Time (LSST) will start in late-summer 2026, revolutionizing transient astronomy. Here, we present the Dark Energy Camera (DECam) Shadow Survey, which is designed to maximize the science potential of LSST by shadowing LSST observations of local galaxy-cluster fields, producing a nightly cadence of these fields. The Shadow Survey will discover extremely young supernovae (SNe), SN precursors, as well as other explosive transients and exotic phenomena, helping to characterize such transients at unprecedented cadence and depth when combined with LSST. We describe our workflow, pipeline, public data releases, and candidate vetting. As an early result of Shadow, we present the fitful luminous blue variable (LBV) eruptions of AT2017des in the Virgo-Cluster galaxy NGC4532. AT2017des has short-timescale variability (of order 10 days), peaking at around $M_r=-12.5$mag, brighter than normal LBVs, and similar to the more extreme flaring of hot LBVs/SN impostors such as SN2000ch, AT2016blu, and the precursor activity of SN2009ip. Our spectral time-series reveals features typical of these hot LBVs and SN impostors/precursors. Combining our data with long-baseline photometry from additional observatories, we find that the peaks of the outbursts of AT2017des are getting brighter over time, with 2026 peak fluxes being up to 5 times greater than in 2023 and an average brightening of $\sim0.05$ mag yr$^{-1}$. The peaks of AT2017des are more luminous than those of most other LBVs, only being fainter than bright precursors such as SN2009ip, and extreme SN impostors such as AT2016blu. AT2017des may therefore be ``ramping up'' to a terminal explosion.

astro-ph.HE↗
arXiv2026

The pair-instability origin of supernova 2023vbw

Stars in the initial and carbon-oxygen core mass ranges of $\sim140-260$ and $50-130$ M$_\odot$, respectively, with low metallicity are predicted to experience copious electron-positron pair production in their cores, leading to a runaway thermonuclear explosion that obliterates the entire star in a luminous and long-duration pair-instability supernova explosion. Some previous supernovae have been interpreted in this context but lack the full range of predicted properties. Here, we report detailed observations and modeling of the hydrogen-rich supernova 2023vbw, which exploded in a low-metallicity ($\sim0.1$ Z$_\odot$) environment in a dwarf star-forming galaxy at a redshift of $0.088$. Its light curve exhibits a luminous ($1.6\times10^{43}$ erg s$^{-1}$) and long-duration ($190$ days) main peak, resulting in a total radiated energy of $3\times10^{50}$ erg, more than an order of magnitude greater than canonical core-collapse supernovae. Semi-analytical light-curve modeling yields a blue supergiant-like progenitor with an ejecta mass of $170-350$ M$_\odot$, radioactive nickel mass of $1.2-1.6$ M$_\odot$, and explosion energy of $(6-13)\times10^{52}$ erg, well matched by pair-instability models. The early and late-phase light curve and spectra also show evidence for interaction of the supernova ejecta with an aspherical circumstellar medium. Discoveries of numerous such events with the upcoming Rubin Observatory and Roman Space Telescope will shed light on the deaths of the most massive stars in the Universe.

astro-ph.HE↗
arXiv2026

SN2023ixf: ultraviolet-to-infrared radiative-transfer modeling of the nebular-phase evolution until 1000 days

We present non-local thermodynamic equilibrium radiative-transfer modeling of SN2023ixf during the nebular phase out to 1000d, using the same ejecta that matched its photospheric evolution, namely a partially stripped red-supergiant star of initially 15Msun whose terminal explosion yielded ejecta with 7-8Msun, kinetic energy of 1.2e51erg, and 56Ni mass of 0.05Msun, augmented with a cold dense shell (CDS) of 0.2Msun at 8000km/s. Interaction with circumstellar material persists at all epochs, powering the ultraviolet (UV) flux at all times, but dominating the optical only after ~600d. Matching the V-band light curve requires invoking both enhanced gamma-ray escape and dust formation after ~200d, first in the CDS and eventually in the inner ejecta as well. Depending on where they form relative to the dust, emission lines are uniformly attenuated or skewed with a blue-red asymmetry. Our models suggest a rising dust mass (chosen as an C-rich and Si-rich mixture) in the CDS and inner ejecta, possibly reaching 1e-4Msun at 700d, while an external cold dust component is required to match the mid-infrared emission. The UV radiation, largely unaffected by dust, is influenced by the emission and absorption from Fe lines, together with strong, blueshifted emission from Lyalpha and MgII2800, both present at >~200d and with a strengthening fractional flux thereafter. Optical-depth effects play a critical role for the UV flux, and most notably on Lyalpha whose strength depends strongly on the CDS structure (mass and extent) and the treatment of power injection. The CDS is continuously slowing down from 8000km/s at 112d to ~6500km/s at 998d, suggesting a growth in mass of several 0.1Msun. SN2023ixf shares many similarities with SN1993J at 1-3yr, but it is eventually fainter due to dust extinction and cooler (i.e., weak [NII] and no [OIII] lines) likely as a result of greater CDS and ejecta masses.

astro-ph.SR↗
arXiv2026

The Eye of Sauron in SN 2025ngs: a Short-plateau Cousin of SN 1998S with Evidence for a Ring-like Circumstellar Medium

Interacting supernovae probe the twilight years of massive stars, exhibiting signatures of interaction between the supernova ejecta and surrounding material expelled from the progenitor. We present the peculiar interacting supernova, SN\,2025ngs in NGC5961 (37.8 Mpc). This transient toes the line between strongly interacting supernovae (type IIn) and type IIP supernovae. SN 2025ngs presents photometrically as a short-plateau supernova, with a plateau duration, t$_{\mathrm{PT}}^{}\approx70$ days. Interaction features subside within a week post-explosion, consistent with the growing number of flash supernovae, giving way to a short period where a typical IIP spectrum is exhibited. Towards the drop off the plateau, interaction features re-emerge, exhibiting complex H$\alpha$ profiles throughout the rest of the transient evolution. We compare with models of early spectra, finding the abundances generally consistent with a supergiant progenitor with a high mass-loss rate (10$^{-3}$ M$_\odot$ yr$^{-1}$). Early, high-resolution spectra reveal a double-horned H$\alpha$ profile, providing strong evidence for shock interaction with a proximate disk-like circumstellar medium. Spectroscopically, SN 2025ngs closely resembles the luminous SN 1998S, despite photometric differences, with SN 2025ngs having a relatively modest peak magnitude of $M_\mathrm{V}=-17.9$ mag, adding another member to the surprisingly diverse 98S-like group.

astro-ph.SR↗
arXiv2026

JWST Nebular Spectroscopy of SN 2023qov: Circumstellar Dust Emission in a Normal Type Ia Supernova

We present panchromatic observations of the Type Ia supernova (SN Ia) 2023qov, ranging from $\sim$2 weeks before to $\sim$1 year after maximum light. \textit{JWST} near- and mid-infrared spectra at $+$276 and $+$363~days show $\sim$400 K dust emission that cools by $\sim$75 K between epochs, the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. We find that the emission is well described by models of carbonaceous dust placed within $\sim$1 light year of the SN, with a dust mass of $\sim$$10^{-4}$ M$_{\odot}$. We do not see evidence of active dust creation, suggesting an infrared light echo by pre-existing circumstellar dust as the likely source of the emission. The \textit{JWST} nebular line profiles suggest asymmetric, stratified ejecta, similar to other normal SNe Ia, though a slight double-horn structure in the argon lines indicate a toroidal enhancement. SN 2023qov exhibits a slightly red, fast-declining early light curve ($\Delta m_{15}(B) = 1.47 \pm 0.05$ mag), from which we determine a $^{56}$Ni mass of $M_{56} = 0.21 \pm 0.04$ M$_{\odot}$, and a distance of $d = 36.0 \pm 1.8$ Mpc to the SN and its host, NGC 7029.

astro-ph.HE↗
arXiv2026

SN2023ixf: Radiative-transfer modeling of the photospheric phase evolution from the ultraviolet to the infrared

SN2023ixf, a Type II supernova (SN) showing early signs of interaction with circumstellar material (CSM), has been observed with unprecedented detail across the electromagnetic spectrum since shock breakout. Here, we present nonlocal thermodynamic equilibrium time-dependent radiative-transfer calculations of its photospheric-phase evolution (i.e., ~20 to ~120d), and for the first time encompassing from the ultraviolet (UV) to the infrared (IR). The explosion of a 15Msun progenitor star, evolved with enhanced mass loss during the red-supergiant phase, yielding an ejecta of 7-8Msun, a kinetic energy of 1.2x10^51 erg, and a 56Ni mass of 0.05Msun, yields a satisfactory match to the photospheric-phase duration and brightness. Prolonged interaction with a decreasing CSM density is required to match a number of salient features of SN2023ixf during the photospheric phase, including the persistent UV continuum and line fluxes, the optical brightness and line profiles (in particular Halpha), as well as the IR flux (interaction boosts the free-free emission at long wavelengths). The presence of a cold dense shell (CDS), which is hard to infer at early times when the CDS and photosphere lie at similar velocities, becomes evident at later times and more so in the IR - we find no evidence for material faster than the CDS at ~8000km/s. Exploratory two-dimensional radiative-transfer calculations based on axially symmetric CSM or ejecta suggest that asymmetry can produce a diversity of profile shapes, with absorption troughs exhibiting a flat bottom or notches at any Doppler velocity. We emphasize the complexity of UV spectra influenced by complex metal-line blanketing at these phases. We document the sensitivity of model results to the adopted clumping in the CDS, though the largest offset is obtained here in the unlikely case of a smooth CDS.

astro-ph.SR↗